Sec.:
Name:
Experiment:
_
Dihybrid Crosses
(B. Science 10-11-3a)
rurpose: To diagram inheritance in dihybrid
~rosses.
~aterials:
brain
~ethods:
~art A: Dihybrid
Cross of Horses
!. In horses, black coats and trotting gait are
lominant while the recessive alleles are white
Ind pacing gait. If the male is homozygous for
~oth dominant traits what is the genotype of the
hale?
What genes are present in the sperms of this
hale?
3. If the female is Yecessive for both traits, what genes are present in the eggs?
4. What is the genotype of the F1 generation?
5. What is the phenotype of the F1 generation?
6. Assuming a male and female are produced in the F1, use these as parents to
produce the F2 generation. Diagram the possible inheritance of the offspring in the
Punnett square in results. Then list the ratio of the phenotypes.
7. Would a dihybrid cross of this type always produce the same phenotype ratio?
Explain
8.. Summarize the genotype ratios of the F2 offspring in results.
Part B: Dihybrid
Crosses of Corn Plants
1. In corn plants, rough seed shape (R) is dominant over smooth seed shape (r) and
y~3110w
seeds (Y) are dominant over white seeds (y). Determine the probable seeds
slnape and color of the F1 generation of offspring whose parents are heterozygous for
the traits by completing the Pun nett square in part B of results.
2. After you have completed the Punnett square in part B, fill in the data table in part B.
t
Besults: Part A: Dihybrid Cross
1. genotype:
2. genes:
3. genes:
4. genotype of F1:
5. phenotype:
6.
__
black - trotters
black - pacers
white - trotters
white - pacers
7. __
, why
8.
BBTT
_
BbTT
_
BBTt
_
BbTt
_
BBtt
Bbtt
of Horses
_
Females_
Genes
Male ~
_
bbTT
bbTt
bbtt
Sec.:
Part
B:
Dihybrid
P, generation
RrYy
I
Crosses
of Corn
. _Name:
._
Plants
RrYy
Female gametes
A
RY
Ry
rY
ry
Ry
JAY
2:16 Phenotypl,:
Genotypic
Ratio
Phenotype
Ratio
smooth.
yellow seed
1:1€
Genotype
rrYy
- ..~~ l:1
RRyy
I
rrYV
RrYV
rryy
Rryy
RRYy
RrYy
I
Conclusions:
1. In a cross of two individuals heterozygous for a single
would be obtained?
trait, what genotype ratio
2. What phenotype ratio would be obtained?
3. What phenotype ratio is obtained when individuals heterozygous for two traits are
crossed?
4. Explain how Mendel came up with the Law of Independent Assortment.
5. Explain if the Law of Independent Assortment would apply if the genes for coat
color and gait in horses were carried on the same chromosomes (meaning the genes
would be physically connected)
6a. As we study inheritance of traits we must keep in mind that because of the fall,
back in the Garden of Eden, we inherit a "sinful nature". Quote the first portion of Rom.
13: 14 to comment on what we should do to not "gratify the desires of the sinful nature".
6b. Quote a portion of Gal. 5: 24 to comment on what Jesus has done to our "sinful
nature" when we belong to Christ Jesus.
6c. Quote a portion of 2 Cor. 5: 17 to comment on what happens to our old inherited
sinful nature when we are "in" Christ.
SELECTED TRAITS IN CATS
Trait
Dominant Allele
Recessive Allele
Coat length
Tabby stripes
Tabby
(T)
Colorpoint
(n)
Colclrpoint (markings
on nose, ears, paws,
and tail)
~how th~ re~ultsof the follow~ngc.rosses using Punnett squares ~nd t~e I
'
mformatlOn In .the accoIlJPanymg
hgyre. (
u r--e,.. (P"'e-.II~.r
+p I f'"\ vluC;I /\-e..eJ'
e..
D;,
(~11'
1ev'\O+~plG.
41\d' p~eI10T:JP[c
~o.s)
lvo:,'VfC/'l.esc.J>r
~
l. Heterozygous 'short-hair X
h
H
peterozygous short-hair
+~
6e.s
h
H
Genotypic ratio:
Phenotypic ratio:
2. Heterozygous tabby X stripeless
t
t
t
Genotypic ratio: '
Phenotypic ratio:
3. Colorpoint X homozygous normal
Genotypic ratio:
, Phenotypic ratio:
-"-,,.-
Name
_
-.
4. Homozygous short, homozygous . colorpoint
~... X
homozygous long, homozygous
normal
hN
'~"
r
-,...-, -..
,
,
-- -Hn
Hn
Hn
--'
, -.
-"!.
hN
hNhN
Genotypic ratio:
Phenotypic ratio:
-
hn hN
... '
HN
Hn ,.
--, -.j
.'
'-
5. Heterozygous short, heterozygous normal X
heterozygous short, heterozygous normal
.. '
..-J__
~,
-+.
1
,
-
Genotypic ratio:
Phenotypic ratio: '
6. Heterozygous tabby, heterozygous
tn
stripeless colorpoint
normal X
'-0-
II
i
I
I -
I
;
tn
-
-j
I
L1
,Genotypic ratio:
Phenotypic ratio:
7. Long-hair, heterozygous
Long-hair, heterozygous
----_.\
normal X
normal
..
'.
hN
hN
..
Genotypic ratio:
Phenotypic ratio: