THEINHERITANCE.INTERACTIONS AND LINKAGE
RELATIONS OF GENES CAUSING YELLOW SEEDLINGS I N
MAIZE*
MERLE T. JENKINS* AND MARTIN A . BELLS
Iowa State College. Ames. Iowa
Received August 22. 1929
TABLE OF CONTENTS
PAGE
INTBODUCTION
..................................................................
Genesl. andl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Genes13andl4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inheritance of l a and of lr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Proof that
13 and 14 are different genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interaction of the four genes producing yellowseedlings with certain other genes for
chlorophylldeficiency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dihybrid ratios involving 11 and if. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dihybrid ratios involving 12,1~,or 14 and ii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dihybrid ratios involving 12, la, or 14 and wg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trihybrid ratios involving 11, if and 12,13 or 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trihybrid ratios involving l&, 1214 or 124 and ii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Linkage relations of 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of 13 with ij . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of l a with y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of 13 with l, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of 18 with genes in the R C linkage group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Is and 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ISand l g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Is and14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IS and Re . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The tetrahybrid LJILJJiiiLJg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Linkage relations of 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of l4with R0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of l4with wg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tests of 1 4 with 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The linkage group LI-LI, R-Wo-Lg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The trihybrid Ld,r*R~Wgwp
...................................................
The trihybrid LJ4rrRoLJ2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chromosome map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SU~AR
. . .Y. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LITERATURE
CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
254
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281
282
* Part of the cost of the accompanying tables is paid for by the GALTON
AND MENDEL
MEMO-
.
RIAL FUND
The data on which this paper is based were obtained in connection with the corn breeding
DEPARTMENT
OF
program conducted by the Office of Cereal Crops and Diseases, UNITED STATES
AGRICULTURE and the Farm Crops Section, IOWA
AGRICULTURAL
EXPERIMENT
STATION,^Ooperating
* Associate Agronomist in Corn Investigations, Office of Cereal Crops and Diseases, Bureau
of Plant Industry, United States Department of Agriculture.
* Formerly Research Fellow in the Department of Farm Crops, Iowa State College.
.
G ~ B T I C15:
S 253 M y 1930
254
M. T. JENKINS AND M. A. BELL
INTRODUCTION
Two genes affecting the production of yellow pigment in maize already
have been reported by LINDSTROM
(1925). He designated themas Zl
(luteus) 'and 12. The present paper reports two additional geneswhich
have been called Is and Z4. The inheritance of both of these genes, their
interactions with a number of other chlorophyll factors, and the linkage
relations of one of them are reasonably well established.
GENES 11 AND 12
Gene Z1 was reported first by LINDSTROM
in 1917. This gene governs the
formation of a distinctyellow pigment but has no effectupon the green pigments. The action of Zl, therefore, may be observed only in such genotypes as suppress the development of the green pigments either partially
or entirely. With the proper genotype the action of Zl may be observed
both in seedlings and mature plants. In the latter, Zl is best known in the
japonica type of striping. With Zl such japonica plants have alternate
stripes of green and yellow, whereas if L1is present the Istripes are green
to occur
and white. With the proper genotype, Zl was found by LINDSTROM
as a pure-yellow or a virescent-yellow seedling. He has summarized the
interactions of Zl (LINDSTROM1925)with the typical seedling genes as
follows :
LIWlV,
ZlWlV)
LlWlV,
LlWlV,
LlWIV,
ZlWlV,
6WlV,
ZlWlV)
green
green
virescent-white
white or albino
white or albino
virescent-yellow
pure yellow
pure yellow
The interaction between Zl and the albino genes w2, and w3 is similar to the
interaction of this gene with w1.
Gene l2 alsowas reported by LINDSTROM
(1925). It differs markedly
from Zl both in its appearance and in its interaction with other known chlorophyll genes. The yellowseedlings are deeper incolor than those produced by h. Gene Z2, unlike 11, produces yellow seedlings by itself and is
lethal in the homozygous recessive condition. In this respect its action is
similar to the various albino genes. LINDSTROM
found that whereas Zl gave
a 12:3: 1 interaction with W1wl, Z2 exhibited a 9: 3:4 relation as follows:
YELLOW SEEDLINGS IN MAIZE
9
3
3
1
L2W1
12Wl
L2wl
12wl
255
green
yellow
white
white
This 9:3 : 4 relationship also held for the albino genes W 2and W3.
Linkage studies (LINDSTROM
1925) with ll and Ez have placed them about
35 units apart in the R-G linkage group. Theorder of the geneson
(1925) is L1-R-W2L2. L1
this chromosome as determined by LINDSTROM
and R are linked very closely if not completely.
GENES 13 AND
14
The l3 and la genes were first observed in 1923 in the seedling progenies
from plants self-pollinated for the first time during the previous summer.
The yellow seedlings produced by these two genes are indistinguishable
from those produced by 12. The parent plant from which la was obtained
came from the commercial variety Iodent, and l4 came from Clark Yellow
Dent. When first isolated l3 and l4 were associated with the chlorophyll
defect, iojap (iJ, the inheritance of which has been reported (JENKINS1924).
Both of these yellow factors, in their interaction with ij, produced some
white-striped-yellow seedlings.When ii was reported it was mentioned
that in some pedigrees segregations of green, white-striped-green, and yellow-striped-green seedlingswere obtained, whilein other pedigrees the
classes were green, white-striped-green, yellow, and white-striped-yellow
seedlings. At that time it was not known whether this was due to two
different factors for striping or two different factors for yellow. It is now
evident that it was due to different factors for yellow seedlings.
INHERITANCE OF
13
AND OF
14
The yellow seedlings produced by both l3 and la are simple Mendelian
recessives to the normal green. Both genes when first isolated appeared
to be linked with lethal or semi-lethal factors which caused a deficiency
in the yellow seedling class and gave distorted 3 :1 ratios. Satisfactory 3 :1
ratios were not obtained until these cultures had been outcrossed and the
disturbing factors eliminated. Critical evidence that the yellow seedlings
produced by both l3 and l4 were simple recessives was obtained, however,
from the proportion of homozygous (LL) and heterozygous (Ll) green
plants in progenies from self-fertilized plants which were heterozygous for
yellow seedlings, and from the proportion of homozygous and heterozygous
plants in progenies resulting from crosses of plants heterozygous for either
GENETICS15: M y 1930
256
M. T.JENKINS AND M. A. BELL
L3 l3 or L414with plants of unrelated stocks. I n the first case the proportion
of homozygous to heterozygous plants should be 1:2 and in the second
case 1:1, if a single Mendelian factor is concerned.
Seedling progenies of the original plant and of 150 other plantsheterozygous for L313have been grown. The progenies contained 12,415 non-yellow
and 3,377 yellow seedlings. This is far removed from a 3: 1 ratio, Dev. +
P. E. being 15.6. A closer approximation to a 3 :1 ratio was obtained from
71 Fr progenies of two crosses between the stock heterozygous for L313and
unrelated stocks. In this case totals of 5,056 non-yellow and 1,576 yellow
seedlings were obtained. Here the Dev. +P. E. was 3.4, still not a particularly good fit.
More critical evidence that only one factor was concerned in the production of Z3 yellow seedlings was obtained from the proportion of homozygous L3L3and heterozygous L313normal green plants in progenies segregating
for these yellow seedlings and in the F1 progenies of the cross L313 X L3Ls.
Among 129 self-pollinated green plants from segregating progenies 48 were
homozygous and 81 were heterozygous. In this case Dev. +P. E. was 1.4,
indicating a good fit. Among 151 self-pollinated plants from Fl progenies
of the cross LJ3X L3L3,80 proved to be homozygous and 71 heterozygous.
The Dev. +P. E. was 1.1 in this case. From these data it seems safe to
conclude that the l8 yellow seedlings are the result of the action of a single
factor.
Progenies have been grown from the original plant and from 75 additional plants heterozygous for L414. These progenies contained a total of
7,672 non-yellow and 2,045 yellow seedlings. Here, again, there is a large
deficiency in the yellow seedling class and very poor agreement with the
expected 3: 1 ratio. The Dev.+P. E. in this case was 13.3. Much better
ratios were obtained among the Fzand F3progenies of a cross between the
lqstock and an unrelated stock. Progenies from 35 heterozygous Fzand FB
plants produced 3,925 non-yellow and 1,231 yellow seedlings. In this case
Dev.+P. E was 2.8, indicating fair agreement between the observed and
expected numbers.
Fifty-eight normal green plants in progenies segregating for Z4 yellow
seedlings were self-pollinated. The progenies from these plants indicated
that 25 of them were homozygous LJ4 and 33 were heterozygous L414.The
Dev. + P . E. for the expected 1:2 ratio was 2.4. Data on the progenies
from 36 self-pollinated F1plants of the cross L414XL4L4indicated that 18
were homozygous and 18 wereheterozygous. These are exactlythe expected numbers on the basis of a 1:1 ratio. It may be concluded, therefore,
YELLOW SEEDLINGS IN MAIZE
257
that the l4yellow seedlings are the result of the action of a single genetic
factor.
PROOF THAT
1 1 , 1 2 13
AND 14 ARE DIFFERENT GENES
LINDSTROM
(1925) has shown that ll and l2 are different. Crosses between
ll and la has demonstrated that these genes are different. The F1 plants
of such a cross are normal green, and under the proper conditions dihybrid
ratios of green to yellow seedlingsare obtained in F2. No crosses have been
obtained between ll and 14. However, the phenotypic differences between
the yellow seedlingsproduced by these two genes,the different interactions
of the respondible genes with other chlorophyll genes, and the fact that
they have different linkage relations leaves little doubt but that theydiffer
genetically.
Genes 12, la and l4 are phenotypically alike, and similar in their interactions with other chlorophyll genes with which they have been tested.
All possible combinations have been made between plants heterozygous
for these genes. The F1 plants in each case have been normal green and
9 :7 ratios of green to yellow seedlingshave been obtained in the Fzgenerathe 9: 7 ratios were modified by
tion. In the case of the cross L21zXL414
linkage as these genes are located on the same chromosome.
INTERACTION OF THE FOUR GENES
PRODUCING YELLOW SEEDLINGS
WITH CERTAIN OTHER GENES FOR CHLOROPHYLL DEFICIENCY
Dihybrid ratios involving ll and ii
Gene ll interacts with ii in a manner similar to its interaction with j as
(1918). The iojap character may be observed in
described by LINDSTROM
the seedlings and for this reason is a better character to work with than
japonica. Self-pollinatedplants heterozygous for L111 Iiii give the following
dihybrid ratio in Fz:
9 L1 I j
3 l1 Ij
green plants
3 L1 ii white-iojap plants
1 ll ii yellow-iojap plants
The white-iojap plants areso named because they have alternate stripes
of green and of white tissue and the yellow-iojap plants because they have
alternate stripes of green and of yellow tissue.
A summary for these two factors is given below:
GENETICSIS: M y 1930
258
M. T JENKINSAND M. A. BELL
L& and Mi
Observed
1420
Expected
Deviations
5969
5919
$50
Llij
Lij
l480
-60
503
493
10
+
x2=3.06
Progenies have beengrown from 33 plants heterozygous for both of
these factors which were backcrossed to the double recessive ( W i ) . Ratios
of 2 green: 1 white-iojap: 1 yellow-iojap seedlings were expected. The data
from these progenies are summarized below:
l; and 1J;
L&
r&
L1
Observed
1545
Expected
Deviations
P=O.Ool
3371
3222
149
+
x2=
1528
l611
-83
1611
66
-
13.87
The poor fit in this case is due to a shortage of iojap plants, and in no
way indicates linkage as there is veryclose to a 1:1 ratio of ,Ll and lI plants
among those recessive for ii.
Dihybrid ratios involving 12, l3 or l4 and ii
When plants of the genetic composition LJ3I i i j were self-pollinated and
their progenies grown, they contained 4 classes of seedlings in the proportions expected on the basis of independent inheritance. The phenotypic
and genotypic description of the seedling classes obtained is given below.
9 L3 Ii green
3 La ii white-iojap
3 l3 I i yellow
1 l3 i i white-striped-yellow
The double recessive class is unusual and is very distinct in progenies
giving a good clear-cut segregation for iojap.
A summary of thedata on 31 progenies from plants heterozygous
for these two factors is given below.
LIlj
Observed
Expected 9 :3 :3 :1
Deviations
2309
2073
+236
x2=116.4
Expected (3 :1 segregation
for i; in the L8 and 1s
classes)
2276
Deviations
+33
X2'
7.88
Zlij
125
691
+34
laZi
516
691
- 175
l.ij
136
230
-94
P =very small
758
-33
489
+27
P10.02
163
-27
SEEDLINGS
YELLOW
IN MAIZE
259
The deviations from the numbers expected on the basis of a 9: 3 :3: 1
ratioare large. Theyare due chiefly tothe deficiencies in boththe l3
classes however. On the basis of the independent inheritance of these two
factors there should be a 3: 1 segregation for non-iojap and iojap plants in
the La and in the l3 classes. The deviations computed on this basis are
much smaller, P having a value of 0.02. The poor fit is due, however, to
deficiencies in the recessive classes and not to linkage.
Data not included in this report show that l2 and l4 give interactions
with ijsimilar to those of 13.
Dihybrid ratios involving12, l3 or laand w 2
LINDSTROM
(1925) has shown that plants heterozygous for l2 and wl,w 2
or w3 give ratios of 9 green, 3 yellow and 4 white seedlings in F2when selfpollinated. The segregations of L212and W 2 w 2are modified by the linkage
between these two factors. Genes l3 and l4 have been crossed with w 2and
give similar interactions. In the case of the cross L k X W 2 w 2the 9 :3 :4
ratio also is modified by linkage.
Trihybrid ratios involving
,lI,
ii and 12, l3 or la
When plants of the genetic composition L111L3131iij
were self-pollinated
and their progenies grown the following classes of seedlings resulted.
3 LIZ3ii ) white-striped-yellow
1 ZJ, ii )pale-yellow-striped-yellow
The triple recessive class is difficult to distinguish from the pure-yellow
seedlings but has been observed. In these seedlings the deep yellow due
to la is suppressed by the ii factor which.in turn allows the lighter ll yellow
to develop.
Data on the progenies from 89 self-pollinated plants heterozygous for
these three factors are presented in table 1.
The datain table 1 do not show a very close fit to the expected numbers.
When all of the yellow seedling classesare grouped together the fit is much
better but still is not very good. The poor fit, however, is due chiefly to
the deficiency of 13 yellow seedlings.
GENETICS 15: M
y 1930
260
M. T. JENKINS AND M. A. BELL
TABLE
1
Seedling progenies from self-pollinated plants of the composition L1lXL3&Ijij.
SEEDINQ
CLASSES
NUMBER 01
PEDIQREE
FROQENIES
QREEN
WEITEIOIAP
YELLOW
YELLOWIOIAP
WEITE
PALE-
STRIPED-
YELLOW-
YELLOW
STRIPEDYEELLOW
18111
1812l
29751
2976l
29802
29812
Totals
1
1
40
29
11
117
205 1
1541
667
7
89
ExPected
(36:9:3:12:3:1)
Debiations
34
21 104
558
356
178
105 357
55
44
138
115
47
39
750
552
208
115
9
71
75
31
12
4837
1252
360
1724
205
14
4721
+l16
l180
+72
393
-33
1574
+l50
393
- 188
- 117
1 I
Rearranged Totals 1943
1252 4837
Expected (36:9:3:16)
4721
Deviations
+l16
360
1180
$72
-393
33
x2=21.47
1
Totals for F2 progenies
71
Rearranged totals
Ex#ected (36:9:3:16)
Deviations
274 969 3813
1401
3813
3731
$82
l31
P =very small
x2=218.7
P=O.OOol
7
7
14
933
$36
1
-37
x2=11.65
-2098
155
1
1
162
13
1576 274 969
1658 31
-82
P=O.009
F* progenies fromplants of the composition .L~i&l&
* F, progenies.
1
Data not included indicate that the progenies from plants heterozygous
for Lll1L.J2I i i j show similar interactions of the three factors but the ratios
are modifiedby the linkage between ll and l2 Progenies segregating for
LlllL.J4I i i jhave not been obtained but the indications are that such progenies would givesimilar interactions but that theratios would be modified
by the linkage between ll and 14.
Trihybrid ratios involving 1213, 1214 or 1314 and i j
When plants of the composition L2l2LJ3Ijii were self-pollinated their
progenies gave the following genotypic and phenotypic classes of seedlings
261
YELLOW SEEDLINGS IN MAIZE
27 L& Ii J green
9L
& ii ) white-iojap
9 L218 Ii
3 l z L ~ii
Data on the seedling progenies from 4 such self-pollinated plants are
recorded in table 2. Because of the usual difficulty in classifying the
white-striped-yellow seedlings, both of the yellow classes have been combined, thus making a 27 :9: 28 ratio of green :white-iojap :yellow seedlings.
Excellent agreement between the observed numbers and those expected
on the basis of independent inheritance was obtained, P having a value of
0.36.
TABLE
2
Seedings progenies from self-pollinated plants of the composition L&&J,ij.
‘RBITB
NLMBER
PEDIQREI
OF PROQENIEI
4
4603
Rearranged totals
Expected (27:9 :28)
Deviations
QREENI
355
355
335
+20
W”8TIUPIID
47
285
108
332
348
108
112
-4
x1=2.07
mmwa
WLLOW8
IOJAPS
- 16
P=0.36
Other data show that similar ratios are obtained when plants of the
I i i are self-pollinated. When plants of the composicomposition L3l3L4l4
tion LzlzLd4Ijii are self-pollinated the ratios are modified by the linkage
between l2 and 14.
LINKAGE RELATIONS OF
l3
Linkage tests havebeen made between .l3 and factors in the R,-Gn,Y-Pz,
B-L, and R-G linkage groups. The data so far obtained indicate that la
is not located in any of these groups.
Tests of l3 and ii
Data already have been presented on l3 and i i in connection with the
Ilii and LZlzL3l3
I j i j . There was
dihybrid L A Iiii and the trihybridsLJ1L313
poor agreement between the numbers observed and those expected on
the basis of indendepent inheritance for the first two of these segregations.
GENETICS
15: M y 1930
262
M. T. JENKINS AND M. A. BELL
For the third segregation, however, P had a value of 0.37 indicating the
independent inheritance of 12, l3 and ii.
The ratios for the dihybrid segregation of L313Iiii were distorted by deficienciesin the recessiveclasses.Crossover
percentages computed from
such distorted ratios would be of doubtful value and so are not included.
The trihybrid LlllL313Ijii, however, probably is worthy of more critical
examination. The crossover percentages between l3 and ii have been computed for this material.
In the progenies from the trihybrid LlllL313Ijii there appeared to be no
linkage between l3 and ii. Seventy-one F2 progenies were used forstudying
any possible linkage between these two factors. Disregarding the segregation for ll the following numbers of seedlings wereobserved and expected :
green
iojap
yellow
striped-yellow
OBmEVED
Ezzpcded
3813
1243
1401
175
3730
1244
1244
414
YULE’Scoefficient of association and OWEN’S(1928) tables showed 37
percent crossing over in the repulsion phase. This situation does not agree
with the manner in which the cross was made. There is an excess in the
yellow seedling class and a large deficiency in the striped-yellow seedling
class. This is due in part to thedifficulty of distinguishing the pure-yellow
seedlings andthe yellow-striped-yellow seedlings. If these two classes
are combined a 9:3:4 ratio results. The expected and observed numbers
on the basis of this ratio are:
OBBDBVED
green seedlings
iojap seedlings
yellow seedlings
3813
1243
1576
For this distribution x2 is 5.90 and P is 0.05. This is not a very close fit
but there is no evidence of linkage. The crossover percentage as determined bya modification of EMERSON’S
(1916) formulasuggested by COLLINS
(1924) was 49.
Probably the most critical data indicating the independent inheritance
of l, and ii come from a study of observed and expected numbers of the
different kinds of F, progeny segregations from the self-fertilized normal
green plants in some of the Fzprogenies mentioned above. The observed
and expected numbers of F3 seedling segregations from such plants, together with the corresponding genotype of the parental Fzplants are recordedbelow.
263
YELLOW SEEDLINGS I N MAIZE
Genotypes of the
normal green Ft plants
Fa seedling segrsgstion
1 L3L3 ZjIj
2 L& zjzj
2 LIL* Ijij
4 L& zjij
all green
3 green: 1 yellow
3 green: 1 iojap
9 green:3 iojap:3 yellow:
1 striped-yellow
OOeerVd
EzpLdul
9
26
25
l1
21
21
35
42
x2 for the above distribution is 3.48 and P is 0.34, showing very good
agreement between the segregations observed and those expected on the
basis of independent inheritance. From this evidence and that previously
presented it seems safe to conclude that Z3 and ii do not belong in the same
linkage group. Unpublished data from recent investigations indicate
that ii is linked with ramosa and glossy 1. This would preclude Z3 from the
R, Gn linkage group.
Tests of l3 with y
Evidence from a study of seedling ratios and the proportions of various
kinds of F3 segregating progenies shows that 1, and y, a factor for endosperm color, are independently inherited. No Fz ratios are available but
a summary of l1 F3seedling progenies is given in table 3.
TABLE
3
Fzseedling progenies from self-pollinated plants of the composition L& Y y.
PEDIQREE
I
NUMBER O?
I
TELLOWENDOSPERM
PBOQENIEB
NON-YELLOW
SEEDLINM)
2981
I
11
Expected 9:3:3:1
Deviations
X1’2.22
855
290
871
- 16
SEEDLINQB
I
WdQ% ENDOSPERM
NON-YELLOW
YELLOW
SEEDLINQ8
BEEDLINQE
290
+10
-8
P~0.53
The segregation agrees excellently with the expected 9: 3: 3 :1 ratio, x2
being 2.22 and P being 0.53. It is realized that a summation of several F3
progenies would obscure a loose linkage as some of the progenies might
exhibit coupling and othersrepulsion and when summed the two conditions
would tend to balance each other. A critical examination of the individual
progenies to determine whether any of them exhibited either the coupling
or repulsion phases of linkage between Z3 and y revealed several progenies
in which coupling or repulsion might have existed. These progenies, however, deviate considerably from the expected 3 to l ratios for yellow and
GENETICS15: MY 1930
264
M. T. JENKINS AND M. A. BELL
white endosperm, and for green and yellow seedlings, preventing an accurate determination of linkage and suggesting that causes other than linkage
were operating to distort the ratios for these particular characters.
Additional evidence from a study of the respective numbers of the several kindsof F3progenies from self-fertilized green F2plants offered further
verification that Z3 and y were notlinked. The observed and expected
numbers of F3 endosperm and seedling segregations from such plants,
together with the corresponding genotypes of the parental F2 plants are
recorded below.
Genotypes of the
Green F, planta
1 L3L3YY
2 L3L3YY
2 L313YY
4 L313yY
1 L3L3YY
2 L&YY
Ft endosperm and
seedling aegregations
All green from yellow seeds
Green seedlings, 3 yellow: 1
white seed
Yellow seeds, 3 green:1 yellow
seedling
endo- both Segregating
for
sperm and seedling colors
All green from white seeds
3 green: 1 yellow from
white seeds
Observed
Ezpected
7
3.1
6.2
4
6.2
16
12.4
2
3.1
6.2
4
4
x2 for
thisdistributionis
3.36 and P is 0.65, indicative of excellent
agreement between the numbers obtained and those expected on the basis
of the independent inheritance of l3 and y. Gene 13, therefore, probably
is not located in the Y-PIlinkage group.
Tests of l3 with l,
The linkage relations of l3 and l,, a simple recessive factor for liguleless
leaves, was studied in the Fz progenies from the cross L3~3~,~,XL313L,L,.
Seedling progenies were grown from 13 self-pollinated plants heterozygous
for these two factors. The data on these progenies are summarizedin
table 4.
Some difficulty was experienced in classifying the yellow seedlings for
the liguleless character. Ordinarily these seedlings were smaller than the
non-yellow seedlings in the same progenies and the ligules were not well
developed. For this reason the two groups of yellow seedlings have been
combined, resulting in a 9:3 :4 ratio.
Data on the F2 progenies indicated that l3 and l, were not linked and
as none of the F3 progenies seemed to indicate linkage between these two
factors the data from the F2and the F, progenies have been combined. For
the F2 progenies P was 0.13 and for all progenies combined P was 0.49.
265
YELLOW SEEDLINGS I N MAIZE
Additional evidence that 13 and l, were not in the same linkage group
came from a comparison of the actual numbers of the various kinds of Fa
progenies with the numbers expected on the basis of independent inheriTABLE
4
Seedling progenies from self-pollinated plants of the composition &laLJr
l
I
NON-YELLOW SEEDLINOS
TELLOW 8EEDLINQS
NUMBER OF
PTiDIQREE
PROQENIEB
1
12
8
1812'
2976'
29812
Totals (F2Progenies)
Totals rearranged
Ezpected (9:3 :4)
Deviations
NORMAL
LIQULELESS
NORMAL
LIQULELWS
106
573
630
26
233
207
36
161
679
679 259
259
197 131
-33
237
+22
1309
1309
1334
-25
466
466
445
+21
712
17
114
74 194
328
316
+l2
x5=4.03
Totals (all progenies) 21
Totals rearranged
Expected (9:3:4)
Deviations
x'=1.48
progenies fromplants of the composition 1aLgLalg.
Fa progenies.
205 391
596
593
+3
P=0.49
1 F2
*
tance. The self-pollinated green F2phenotypes should segregate in the Fa
as shown:
Fa aeedting wegations
All green
3 green: 1 liguleless green
3 green :1 yellow
9 green :3 liguleless green:3 yellow :1
observed
E z M
2
8
8
9
3.1
6.2
6.2
12.4
4
6
3.1
6.2
liguleless yellow
All iiguleless green
3 liguleless green: 1 liguleless yellow
The value of x2 for the distribution above was only 2.51 and P was 0.77.
This is an exceptionally close fit and indicates that Z3 does not belong in
the B-L, linkage group.
Tests of l3 with genes in the R-G linkage groz@
Gene l3 also has been tested for linkage with the following 4 factors
GINBTICS15: My 1930
266
M. T. JENKINS AND M. A. BELL
located in the R-G linkage group, 11, 12, 14, and Rg. The tests with each of
these factors have indicated that l3 is not located on this chromosome.
l3 and lI
Possible linkage relations between l3 and ll may be studied in the Fzprogenies from the trihybrid Ll11L31311ij
presented in table 1 and already discussed. The observed numbers do not fit closely those expected on the
basis of independent inheritancebut thepoor fit appears tobe due to causes
other than linkage between these two factors.
l3 and l2
A summary of the dataon 6 Fz progenies from plants of the genetic composition 12L3L213
is given below:
Non-yellow seedlings
Yellow seedlings
Observed
Ex9eckd
Deviation
724
498
687
535
+37
-37
The deviation from the 9:7 ratio expected on the basis of independent
inheritance is 3.1 times its probable error. The deviation, however, is in
the wrong direction to indicate linkage. There is a large deficiency of yellow seedlings whereas there should have been an excess of yellow seedlings
if these two factors were linked as they came into the cross from opposite
parents.
l3 and 1,
Gene l4 is located in the R-G linkage group as will be shown by data to
be presented later. Data are available on 9 progenies of F1 plants of the
composition L31413L4.The data on these progenies are summarized below:
Green seedlings
Yellow seedlings
ObeerVed
Ezpcded
Deviation
92 1
677
899
699
- 22
+22
There is fairly close agreement between the observed and the expected
numbers. Dev. +P. E. is 1.7. Here, again, the deviations are in the wrong
direction to indicate linkage.
l3 and
R9
Genes lI and R9 are linked very closely, if not completely. As Z3 appeared
to be independent of 11 it naturally would be expected to be independent
of RE.Such provedto be the case. The data on l3 and RVcome from 15 F2
267
YELLOW SEEDLINGS I N MAIZE
progenies from plants of the composition L3Rg13rr.A summary of the data
on these progenies is given below.
Observed
L/-Non-yellow seedlings with red stems
L3Rg-Non-y ellow seedlings with green stems
l&-Yellow
seedlings with red stems
laRg-Yellow seedlings with non-red stems
757
276
221
122
Ezpected
Deviation
774
- 17
258
258
86
+l8
-37
+36
The excess of yellow seedlings with non-red stems is due to the difficulty
of distinguishing red stem color on the small yellow seedlings. If all of the
yellow seedlings are grouped together much better agreement is obtained
between the expected and observed numbers. The results with this grouping, which gives a 9 :3 :4 ratio, are asfollows :
Observed Expected Deviation
757
774
- 17
Non-yellow seedlings with red stems
276
258
18
Non-yellow seedlings with green stems
343
344
-1
All classes of yellow seedlings
+
P is 0.46 for the abovedistribution,indicatingvery
close agreement
between the numbers observed and those expected on the basis of independent inheritance.
Tetrahybrid LlllL3131iLplo
In the linkage studies with Z3 a number of interesting trihybrid and
tetrahybrid segregations were obtained and it was thought worth while
are
to report one of them. When plants heterozygous for L111L3131jijLplo
self-pollinated the following genotypic and phenotypic classes of seedlings
should result :
green
green
liguleless-green
yellow
white-iojap
yellow
yellow-iojap
liguleless-green
:white-striped-yellow
liguleless-yellow
liguleless-white-iojap
pale-yellow-striped-yellow
liguleless-yellow
liguleless-white-striped-yellow
ligueless-yellow-iojap
liguleless-pale-yellow-striped-yellow
GENETICS15: M y 1930
268
M. T. JENKINS AND M. A. BELL
Assuming independentinheritance of these four factors, the various
phenotypic seedling classes and the observed and expected numbers from
four progenies are tabulated below:
Ratio
108
36
36
27
12
9
9
9
3
3
3
1
Phenotypes
green
liguleless-green
yellow
white-iojap
liguleless-yellow
liguleless-white-iojap
yellow-iojap
white-striped-yellow
liguleless-yellow-iojap
liguleless-white-striped-yellow
pale-yellow-striped-yellow
liguleless-pale-yellow-striped-yellow
Oberved
Ezpected
137
60
44
151
50
29
3
39
17
13
13
13
4
4
4
2
I
46
9
14
7
7
1
50
The above distribution even though in fairly good agreement with the
expected does not lend itself to statistical analysis because of certain deviationsinthe yellow-seedling classes which arerelativelylarge,owing,
perhaps, to difficulties in correctly classifying striped-yellow and liguleless-yellow seedlings.
If all of the yellow seedling types, exclusive of yellow-iojap, are combined, much better agreement between the actual and calculated numbers
is obtained. These results are shown below:
Ratio
Phenotypea
Oberd
Ezpeded
108
36
27
9
9
3
64
green
liguleless-green
white-iojap
liguleless-white-iojap
yellow-iojap
liguleless-yellow-iojap
yellow seedlings of all classes
137
60
151
29
9
39
13
13
4
90
50
14
7
103
Deviation
- 14
+10
- 10
- 4
+ l
+3
13
+
The size of x2 for the above distribution was 11.30 and the value of P,
0.08. This fit, although not extremely good, tends toverify the hypothesis
of independent inheritance of the four factors, ll13iilg.
LINKAGE RELATIONS OF
14
Linkage tests with l4 have shown that this factor is located in the R-G
linkage group. Linkage data have been obtained with three factor pairs of
this group, namely Rr, L.& and Wzwz.
269
YELLOW SEEDLINGS I N MAIZE
Tests of l4 with R0
Determinations of the linkage between l4 and R0 come from data on a
number of F2 and F3seedling progenies fromplants heterozygous for these
two factors. The factor RQis expressed in the seedlings as a green or at
least a non-red stem, whereas seedlings carrying the factorrrhave red stems
(provided, of course, that A is present).
Data on 6 progenies showing the repulsion phase of the linkage and 4
progenies showingthe coupling phaseof the linkage are recorded in table 5 .
TABLE
5
Data on the progenies from self-pollinated plants of the composition L W R g .
I
RED STEMS
PEDIQREE
NON-RED STEMS
QREEN
YELLOW
QREEN
YELLOW
SEEDLINGS
SEEDLINGS
SEEDLINGS
SEEDLINQS
Repulsion
4606- 7
-1 1
577z-4
5775-17
5776-14
-16
Totals
Expected, 37 percent
crossing over
Deviation
66
152
114
67
103
110
20
65
38
62
43 36
31 24
36
37
50
44
612
239 247
607
+5
245
-6
3
10
5
1
11
9
39
I
245
+2
P=very good fit
39
0
Coupling
5773-34
-41
5775-39
5776-37
Totals
Expected, 36 percent
crossing over
Deviation
46
37
209
179
13
12
78
11
7
7
66
21
3
3
35
27
471
114
101
68
454
+l7
111
+3
- 10
111
77
-9
x2=2.67
P=0.45
The 6 repulsion progenies showed 37 percent crossing over and the 4
coupling progenies 36 percent crossing over. These two crossover percentages are in very close agreement.
Three of the repulsion progenies recorded in table 5 were Fzprogenies
segregating for aleurone color. The genetic composition of the parental
plants was L4RgC/l4rrc. The progenies fromtheseplants
showed 3 : 1
GENETICSIS: MY 1930
270
M. T. JENKINS AND M. A. BELL
ratios of red to non-red stems and :97 ratios of colored to colorless aleurone.
The repulsion phase of the linkage was exhibited by the stem color segregation and the coupling phase by the aleurone segregation. This peculiar
situation is due to the action of the factor RQwhich is dominant inaleurone
color and recessive in stem color. LINDSTROM
(1925) described a similar
situation in discussing the linkage of L, and RQ. The complete data on
these three Fz progenies are recorded in table 6.
Data on the
PEDIGREE
I
I
F2
TABLE
6
progenies from plants of the composition L,RgC/lrr'c.
l
COLORED ALEURONE
I
RED STEM8
1
NON-RED STEM8
1.
37
-1 1
5775-17
Totals
35
42
18
2
6
18 1
129
91
9
13
156
COLORWBB ALEURONE
1
RED STEMS
NON-mD STEMS
L
L,
1.
25
74
30
11
52
7
20
6
1
4
0
81
33
5
L4
A summary of the data in table 6 to show the repulsion phase of the
linkage between L414and rrRQappears below:
L,I
L,J
Observed
124
Ezpected, 3 2 percent
crossing over
Deviations
285
l
a
l.?
116
121
$3
283
+2
x*=0.30
121
-5
P = very good fit
14
14
0
Another summary of these data to show the coupling phase of the linkage between these two factor pairs appears below:
Colored Aleurone
L
Observed
Expected, 30 percent
crossing Over
Deviations
~2-1.77
247
252
-5
86
Colorlese Aleurone
k
4
44
162
51
+10
-7
152
k
84
+2
P~0.62
These data indicate a modified 27 :9: 2 1 :7 ratio. The crossover percentage
was computed using a'modification of EMERSON'S
(1916) general formula
described by BRUNSON(1924) for use in trihybrid ratios involving two
compIementary genes, one of which is linked with a third gene.
271
YELLOW SEEDLINGS IN MAIZE
The crossover percentages of 32 and 30 computed from these two distributions are slightly lower than those of 36 and 37 computed from the
data in table 5. The value of 36 percent has been selected as themost
likely value as it is based on coupling progenies and also because it fits
better than the lower values certain data presented later in tables 11, 12,
13 and 15.
Tests of l4 with w2
The data on the linkage relations between l4 and wz come from 77 Fa
seedling progenies of the cross L4L4W2w2XL4Z4W2W2.
In as much as these
were F3progenies, some of them showed the coupling phase of the linkage
and others the repulsion phase. The summarized data on these progenies
are recorded in table 7.
TABLE
7
Data on the Fa seedling progenies exhibiting the coupling and the repulsion phases of
linkage between 14 and m.
PEDIQREE
5773
5774
5775
5776
Totals
Expected, 35 percent
crossing over
Deviation
NUMBER OF
PROQENIES
4
7
BEEDLINQS
Coupling
396
667
31
772
3217
749
3140
+77
16
8
17
5
Totals
l
46
Expected, 40 percent crossing over
Deviation
x2=21.84
I
86
147
375 1465
164 689
14
6
x2=10.21
5773
5774
5775
5776
YELLOW
QREEN SEEDLINQS
+23
SEEDLINO
126
253
569
248
1196
1296
- 100
P-0.006
Repulsion
1298
425
1720
485
3928
3818
+l10
-
542
169
658
167
1536
1485
+51
P=0.00002
563
177
690
176
1606
1766
- 160
The crossover percentages were computed from a modification ofEMERSON’S formula suggested by COLLINS(1924) for use with a 9: 3 :4 ratio.
The data in table 7 indicate 35 percent crossing over between 1 4 and wz
for the coupling progenies and 40 percent for the repulsionprogenies.
GENETICS15: M y 1930
272
M. T. JENKINS AND M. A. BELL
The poor fit in both the coupling and the repulsion progenies is due largely
to the deficiency of white seedlings. This deficiency results from the very
close linkage between W, and a factor for defective seeds, d,. This linkage
(1923). The defective seeds germinated only
was reported by LINDSTROM
91 percent, whereas the normal seeds gernimated 97 percent.
An opportunity to verify the crossover percentages computed from the
seedling ratios presented itself in a study of the proportions of the different
kinds of F3 segregatiops. It will be recalled that Z4 and W, came into the
cross from opposite parents and the repulsion phase of the linkage would
be expected in F,. The closeness of the linkage between these two genes
will be reflected in the proportions of the various kinds of F3 progenies
from self-pollinated F, green plants. The theoretical F, populations were
computed assuming 35, 40 and 44 percent crossing over respectively and
the proportions of the different kinds of Ft segregations determined.
Table 8 shows a comparison of the observed and expected numbers of
F3progeny segregations. A total of 146 Faprogenies is available for study.
The x2 test for goodness of fit has been determined between the observed
numbers of F3 segregations and those expected with 35,40 and 44 percent
crossing over. The best
fit was obtained when 35 percent crossing over
was assumed, although each of the crossover percentages given fits well
within the limits of chance variations, P in the case of 35 percent crossing
over being greater than 0.80.
TABLE
8
Observed numbers of the different kinds of F J progeny segregations from F1 plants of the
composition La&Wz and those expected with 35, 40, and 44 percentages
of crossing over.
F1 SEEDLING SEGREGATIONS
CROSSOVER
PERCENTAGE
RREEDINQ
SEQREQATINQ
TRUE FOR
FOR
Observed
Expected, 40 Percent
crossing over
8
I
8
8
P=0.56
Observed
Expected, 44 percent
crossing over
I
1
31
28
32
x2=2.05
8
13
x2=4.51
Modified by the linkage between I 4 and W*.
28
33
I
I
SEQREQATINQ FOR
3 QREEN: 1
YELLOW
28
xz=0.47
P
lI
FOR
WHITE
GREEN
Observed
Expected, 35 percent
crossing over
SEQREQATINQ
3 QREEN: 1
9 QREEN: 3 YELLOW: 4
WEITE~
"___
33
77
31
75
1
I
= greater than 0.80
33
32
33
33
P=0.22
77
70
77
66
273
YELLOW SEEDLINGS IN MAIZE
Tests of l4 with l2
The percentage of crossing over between l4 and l2 was determined from
the Fz seedling progenies of the cross L212G4L4
X L2L2La14.
The complemena 9: 7 ratio of green to yellow
tary interaction of these two factors produced
seedlings modified slightly by linkage. The summarized data on 10 F2
progenies are recorded in table 9.
F2
TABLE
9
seedling progenies from self-pollinated plants of the composition I&/lZL,.
I
DBV +p.m. 9:
BEEDLINQ CLASSES
YEUOW
5771
Expectcd, 9 :7
Deviation
Expected, 43 percent
crossing oaer
Ceviation
10
1
1
1156
963
1192
36
927
"36
1157
-1
962
-
+l
7
-
2.4
0.7
The data in table 9 indicate 43 percent crossing over between 12 and 14.
The deviation from the numbers
expectedon the basis of independent
inheritance is only 2.4 times the probable error. The deviation however is
in the direction of an excess of yellow seedlings which would be expected
if the two factors were linked. In view of the usual deficiences obtained
in the yellow seedling classes an excess in this case is of added significance.
Recognition that any deficiency of yellow seedlings would tend to increase the percentageof crossing over when calculated by theformula used
(a modification of EMERSON'S
formula for 9: 7 ratios) would suggest, perhaps, that 43 percent was slightly high. Because of that possibility, it was
assumed that all kernels not germinated were potentially yellow seedlings.
The ratio then became 1156 green and 1012 yellow seedlings from which
37 percent of crossing over was calculated. Thisvaluerepresentedthe
lowest possible percentage of crossing over obtainable from the data at
hand, indicating that l2 and l4 were linked weakly even by the most conservative estimation.
Forty-three percent crossing over between .l4 and l2 was decided upon
as being more nearlycorrect.This
figure agreedremarkable well with
the calculations of crossover values between otherfactorswithin
the
linkage group.
GENETICS15: M y 1930
2 74
M. T. JENKINS
AND
THE LINKAGE GROUP
M. A. BELL
L4 - L1, R - W2-L,
LINDSTROM
(1925) indicated thatthe probablearrangement
of the
genes he studied was Ll,R- W,- L,. L1 and R probably are completely
linked, and he obtained about 22 percent crossing over between L1 and W ,
and about 35 percent crossing over between R and L,. Data already presented in this paper indicate
that L, is about 36 units from R , 35 to 40 units
from
and 43 units from L,. This situation would indicate that L, probably is located to the left of R, although if this is the case the distances
from L, to R and from L, to W zdo not seem to be in very close agreement.
The best proof that thisis the real situation could,of course, be had from
backcrosses involving Z4 and l, or more of the other factors on thischromosome. In as much as 3 of the genes studied (1, 1, and W,) are lethal, backcrosses were not possible. The bestavailable
proof thatthisisthe
correct order of these genes comes from data on 2 trihybrid segregations,
one involving 14, Rg and W , and the other involving l,, R9 and lZ.
W,
The trihybrid LJgrRgWzw2
This trihybrid was the result of the cross L4L4rTR~W2w2XL4l4rrrrW2W2.
The F1 plants of this cross would be expected to be of S different genotypes
L4rrW2/L4rrW2,
lqrrWZ/L4rrW2,L4rrW2/L4rTw2,lqrrW2/L4rrwz,
L4rrW2/L4Rg
W 2 ,lqrrWz/L4RgWz,
L4rrW2/L4Rgw2,
1 4 r r W 2 / L 4 R ~Twelve
~ 2 . F1plants were
self-pollinated. Three of these plantsproved to be of the genotype, Z4rrWz/
L2R~w2.
The F, progenies from two of them were grown in the field and
135 L4rrW2plants (green plants with red stems) were self-pollinated. Some
of these plants proved to be homozygous for all 3 of the factors involved,
some were heterozygous for 1, some for 2 and some for all 3 of the factors.
The F, progenies from plants heterozygous for all 3 genes (57 in all) furnish the most critical evidence that the order of the genes is L4 - R0 - W2.
Four different genotypes were expected amongthe self-pollinated FZ
plants that were heterozygous for all 3 genes. These four genotypes and
their F3 linkage relations are shown below:
F, genotype
1.
2.
3.
4.
k'wz
F, linkage relations
LdRgW2
Repulsion between l4and RP,and between 14 and wz and COUPbetween
ling
RI and w2.
L6Wz
&RPWz
Coupling between l4 and R I , between 1, and W Z , and between
RE and wz.
L
L4RoWz
Repulsion between lr and RP, coupling between
and repulsion between RE and wz.
lrRoW2
L,r'w*
Coupling between l, and Rg, repulsion between 1, and wz and
between R9 and W*.
1,Vwz
and
W
2 7.5
YELLOW SEEDLINGS IN MAIZE
Each of the 57 progenies from trihybrid F2plants was examined to determine the genotype of the parental Fz plant. Progenies were obtained representing the first three parental genotypes.
If thearrangement of the genes
is L4-Rg-W2 the fourth parental genotype represents the double crossover combination of these three genes and would be expected to occur less
frequently than the non-crossover or single-crossover combinations. No
FBprogenies representing this parental genotype were obtained.
A summary of the dataon all of these progenies from which the crossover
percentage between R0 and w 2was computed is recorded in table 10. Data
on the coupling progenies indicate 17 percent of crossing over between
these two factors and data on the repulsion progenies indicate 13 percent
of crossing over.Inasmuch
asthenumbers
were muchlarger in the
coupling progenies the value of 17 percent has been used in computing
the expected numbers for the Faprogenies of the different Fz parental genotypes. The poor fit in thecoupling progenies is due to thedeficiency of white
seedlings. This value is intermediatebetween that of 15.4 previously
TABLE10
Data on the F3 progenies jrom F Zplants of the composition rRoWowz.
NON-WHITE BEEDLINQB
PEDIQREE
NUMBER OF
PROQENIEB
I
WHITE SEEDLINQS
RED
NON-RED
RED
NON-RED
STEMS
BTEMS
STEMS
8TEMS
CO?,
'ing
5773
5774
5775
5776
15
6
28
4
1540
464
3337
507
178
55
448
81
139
50
343
45
385
121
Totals
Expected, 17 percent
crossing over
Deviation
53
5848
762
577
1411
5780
68
+93
669
1481
- 70
x2=29.69
+
5773
5774
5775
5776
1
2
1
1
RePulsion
107
201
95
91
Totals
Expected, 13 percelzl
crossing over
Deviation
5
494
128
-92
P = very small
41
98
43
57
46
92
41
45
239
224
1
0
2
1
I
4
4
0
485
+P
x0=0.82
GENETICS15: M y 1930
669
777
P =very good fit
M. T. JENKINS
2 76
AND M. A. BELL
reportedby LINDSTROM
(1924) between the same two factors and that
of 22 reported by him (1925) between L1 and W,.
Unfortunately it was difficult to computethe crossover percentage
between l4 and R0 due to the presence of wz.The linkage between w 2and
genes l4 and R0 resulted in unequal suppression of l, classes by W, and made
any calculation of linkage between l4 and R0 difficult and uncertain. For
this reason the crossover value of 36 percent arrived at from the data in
table 5 has been used in computing the expected numbers for the Fa progenies of the different F, genotypes.
Assuming 36 percent crossing over between l4 and Ro and 17 percent
crossing over between Ra and W,,a double crossover percentage of about 6
would be expected if there were no interference. The theoretically expected
numbers have been computed on the basis of these crossover values.
Theparentalgenotype
l4rrW2/L4R~w2
With the crossover percentages mentioned above the relative frequency
of the gametes produced by this parentalcombination would be as follows:
Method of gamete formation
Gametic ratio
53
30
11
6
6
11
30
53
Parental type
Crossover in the L4-Rg region
Crossover in the RO-WI region
Double crossover
Double crossover
Crossover in the RO-WZ region
Crossover in the LrRO region
Parental type
TABLE
11
Seedling progenies from self-pollinated plants of the composition lqrWz/L&'wr.
WHITES
YELLOWS
QWENS
PZDIQREE
NUMBER OF
PROQENIES
RED
STEMS
NON-BED
STEMS
RED
NON-RED
STEM0
STEMS
NON-RED RED
STEMS
~
5773
5774
5775
5776
Totals
Expected'
Deviation
13
5
17
1
901
234
1469
92
2687
+9
131
38
251
22
442 2696
385
+57
401
98
62 1
36
1156
1122
-34
6
37
3
38
206
11
68
56
+l2
368
441
-73
BTEYB
"341 113 22
79
484
33
~ _ _
937
976
-39
xz=25.71
P=O.O001
Calculated on the basis that there was 36 percent crossing over between La and R,, 17 percent crossing over between Rg and W1,and 6 percent of double crossing over.
277
YELLOW SEEDLINGS IN MAIZE
By arranging these gametes in an ordinary trihybrid Punnett square
and multiplying them by their relative frequencies, a theoretical phenotypic population can be derived, which should agree with the one observed,
provided the linear order of the genes andtheir distances apart have
been correctly assumed. In table 11 are summarized the results from 36
progenies. The agreement between the observed and expected numbers is
not very satisfactory due to the deficiency of white seedlings. This deficiency is due to the linkage between W, and dl.
Theparentalgenotype
L4rrWz/14R@wz.
Assuming the same crossover percentages as before. the gametic ratio
for this parental combination would be as follows:
Gametic ratio
53
30
11
6
6
11
30
53
Gamete
Methcd of m e t e formation
LNW,
Laow,
L47TWP
Laow2
Parental type
inCrossover
4-Rg region
Crossover in the R 0 - w ~region
Double crossover
Double crossover
Crossover in the Ro-W, region
inCrossover
LC"# region
Parental type
the
Wwa
1a9w2
wwz
the
1agwWz
Data on 17 progenies from Fz plants of this genotype are recorded in
table 12.
TABLE
12
Seedling progeniesfrom self-pollinatedplants of the composition LdrTW,/ldRows.
PEDIQBEE
NVNREB OF
PROQENIEB
5773
5774
5775
5776
RED
NON-RED
m D
NON-RED
RED
NON-mD
mm8
BrnW
STBY8
mw
mm
BTEYB
2 47 191
l
103
11
216
1031
3
305
16
9
93
41
26
29
137
74
9
2
67
15
44
12
34
42
293
95
"
Totals
Expected'
Deviation
17
1630
159
366
93
209
474
1587
134
383
94
228
-19
505
+43
x*=10.08
+25
- 17
-1
-31
P=0.07
Calculated on the basis that there was 36 percent crossing over between LCand R@,17 percent between R0 and W2 and 6 percent of double crossing over.
1
GENETICS15: My 1930
278
M. T. JENKINS AND M. A. BELL
The fit in this case is much better, P being 0.07. There is a deficiency
of white seedlings and an excess of green seedlings with non-red stems.
The parental genotype l4rrw2/L4R0W2
The expected gametic ratio for thisparental combination, with the
crossover percentages previously mentioned, would be as follows:
Gametic ratio
Gamete
Method of gamete formation
Parental type
Crossover in the L4-Rg region
Crossover in the Rg-Wz region
Double crossover
Double crossover
Crossover in the Rg-Wz region
Crossover in the L4-Rg region
Parental type
53
30
11
6
6
11
30
53
The theoretical numbers of each phenotype were calculated in a manner
similar to that previously described.
This parental genotype was represented by only four seedling progenies.
The data on these progenies are recordedin table 13. The agreement
between the observed and theexpected numbers was very close, P having a
value of 0.54.
TABLE13
Seeding progenies from self-pollinated plants of the composilion lJ'wz/L&Yw~.
QREEN 8EEDLINQS
PEDIQREE
YELLOW SEEDLINGS
SF3iDLINQS
NWMBER OP
PROQEmS
RED
smyB
"
5774
5775
5776
Totals
Ezpectedl
Deviation
2
1
1
69
"
87 159
37
45 69
48
-___
"4
297
288
+9
x2=4.11
172
I62
+l0
17890
26
101
6 24
- 11
+2
186
-8
-3
P-0.54
1 Calculated on the basis that there was 36 percent crossing over between L, and Re, 17 percent between RV and W Z ,and 6 percent of double crossing over.
With the crossover percentages previously mentioned (36 percent between l4 and Ro, 35 to 40 percent between l4 and w2 and '17 percent between
SEEDLINGS
YELLOW
279
IN MAIZE
and wz)there may be some doubt as towhether the order of these genes
z RI - W z-Lq. With only 17 percent crossing over between
is LP-R I - Wor
RPand W zit seems extremely unlikely that the order could be Ra-L4- W z
With such an arrangement LPwould have to be closely linked with both
RI and W z instead of loosely linked with them.
In order to determine which of the first two arrangements was the more
probable the theoretical ratios expected with the order . R * - - W z - L 4 were
computed for the data in tables 11, 12 and 13. The values of x2 then
were computed and are shown in table 14 in comparison with the x 2 values
computed for the order LP- Ra- W2.
R g
TABLE
14
The x2 valuesfor the expected ratios in tables 11, 12, and 13 with the gene orders
LrRo-Wp and Ro-WrL,.
TABLE NUMBER
I
I
LrRp-Ws
Rg-WrL.
64.70
11
12
13
10.08
4.11
Totals
39.90
25.71
43.31
4.27
112.28
The x2values in table 14 indicate that the orderLP- R9 - W zis probably
the correct arrangement of these genes.
The trihybrid Ld4rrRaL2lZ
Additional information indicating that l4 occupied a locus to the left of R
is supplied by the F1progenies of the cross L4L4rrRgL2k
X L41PrrrrLzLz.
The
F1plants of this cross wereof several different genotypes. Those heterozygous for all three factors wouldbe represented by the genetic formula
lPrrLz/L4R~lz.
The F2 progenies from these plants wouldshow coupling
between RI and l2 and repulsion between l4 and R0 and between l4 and 12.
It was not possible to compute the crossover percentages between LP
and R and between Lz and R from these progenies. Therefore, the value
of 36 percent previously determined was assumed between L4 and REand
(1925) was assumed between
that of 35 percent reported by LINDSTROM
L1 and RV. On the basis of these two assumed values, andthe order
GENETIC$15: M y 1930
2 80
M. T. JENKINS AND M. A. BELL
L 4 - Rg-Lz, about 13 percent of double crossing over would be expected.
The expected gametic ratios, therefore, would be as follows:
Gametic ratio
Method of Gamete formation
Gametes
42
22
23
13
13
23
22
42
Parental type
Crossover in the RU-LI region
Crossover in the L,-Ro region
Double crossover
Double crossover
Crossover in the L,-Rg region
Crossover in the RQ-Lzregion
Parental type
The factorial interactionof this trihybridproduced a modified 27 :9 :2 1 :7
ratio of greens with red stems, greens with non-red stems, yellows with
red stems and yellows with non-red stems. A comparison of the observed
numbers of seedlings in each of these phenotypic classes with the expected
numbers calculated according to the gametic ratios assigned is shown in
table 15.
TABLE
15
Seedling progenies from self-pollinated plants of the genetic composition lJ'La/L&Olr.
5
423
112
303
112
404
119
308
-7
-5
119
-7
5771
Expected'
Deviation
+l9
x2=
1.80
P~0.62
Calculated on the assumption that there was 36 percent of crossing over between L, and R@
and 35 percent between R0 and L%and 13 percent of double crossing over.
The crossover percentages assumed for computing the expected distribution evidently must be fairly correct as the fit is very good, x2 being
only 1.80 and P being 0.62.
CHROMOSOME MAP
According to the results obtained in this study, supplemented by work
who determined the R - W 2-L2relationship,
already done by LINDSTROM,
281
YELLOW SEEDLINGS IN MAIZE
the order of the four factors with their approximate crossover percentages
is as shown in the diagram below:
R
l
1
W2
17
36
4
3
1
k2
I
I
The interrelations of these crossover percentages when the double crossover values are taken into account are in very close agreement. For example, the crossing over between L4 and Lz was 43 percent as determined
from data involving these two factors only. Crossing over between L4
and R, and R and Lz was 36 and 35 percent, respectively, which would
mean about 13 percent of double crossovers in the three factor relation
L,- R-L2. As double crossing over reduces the actual amount determined between any two factors in a series, the total crossover percentage
between L4and L2should be 43 percent plus twice 13 percent or 69 percent,
which agrees very well with 71 percent, the sum of crossover percentages
between L4 and R,and R and Lz. Another three factor relation, La- RW z ,furnished similar data. The double crossovers here were calculated to
be about 6 percent as the percentages between L4 and R, and R and W2
were 36 and 17 percent, respectively. About 35 or 40 percent of crossing
over existed between L, and W z to which amount should be added twice
the double crossover percentage, making a total of 47 to 52 percent. The
sum of the crossover percentages from L4 to R and from R to W 2is about
53 percent. If the correct distance from L., to R is 36 units probably the
distance from La to W 2is at least 40 units or more, rather than 35.
SUMMARY
Two new lethal factors for yellow seedlings in maize, both simple recessives, are reported. The allelomorphic factor pairs are designated L313and
Ld4.
The interaction of these twogenes with the two previously reported
genes producing yellow seedlings and with certain other chlorophyll genes
also is described. Genes l3 and l4are similar to l2 in their interactions with
other chlorophyll factors.
The linkage group to which l3 belongs was not determined. I t showed no
indication of linkage with certain members of the R - G , B - L g , Y -P1
and Ra -Gu linkage groups.
GENETICS15: M y 1930
282
M. T. JENKINS AND M. A. BELL
Gene l4 showed linkage with 3 members of the R - G linkage group. Its
most probable location appears to be 36 units to the left of R.
The order of the four genes of this linkage group included in this study
appears tobe L4- R - W z-Lz.
LITERATURE CITED
BRUNSON,
A. M., 1924 The inheritance of a lethal pale green seedlingcharacter in maize. Mem.
Cornell Agric. Expt. Sta. 72: 1-22.
COLLINS,
G. N., 1924 Measurement of linkage values. J. Agric. Res. 27: 881-891.
EMERSON
R.A., 1916 The calculation of linkage intensities. Amer. Nat. 50: 411420.
JENJLINS, M. T.,1924 Heritable characters of maize, 20-Iojap striping. J. Hered. 15: 467472.
LINDSTROM,
E. W., 1917 Linkage in maize: aleuroneand chlorophyll factors. Amer. Nat. 51: 237255.
1918 Chlorophyll inheritance in maize. Mem. Cornell Agric. Expt. Sta. 13: 1-68.
1923 Heritable characters in maize 13. Endosperm defects-sweet defective and flint defective. J. Hered. 14: 127-135.
1924 Complementarygenes for chlorophyll development
in maize and their linkage relations.
Genetics 9 : 305-326.
1925 Genetic factors for yellow pigment in maize and their linkage relations. Genetics 10:
422455.
OWEN,F. V., 1928 Calculating linkage intensities by product moment correlation. Genetics 13:
80-1 10.