15.2. 1972
223
Specialia
Fig. 4. Karyotype of a female B. b.
bengalensis collected from Rohru,
Himachal Pradesh. • 2000.
s a m p l e a n d it is l a r g e - s i z e d a c r o c e n t r i c c h r o m o s o m e in t h e
o t h e r t w o samples. This v a r i a t i o n in t h e m o r p h o l o g y of
t h e X c h r o m o s o m e could h a v e b e e n b r o u g h t a b o u t b y a
p e r i c e n t r i c inversion. S p e c i m e n s w i t h a c r o c e n t r i c X
c h r o m o s o m e are s e p a r a t e d b y m o r e t h a n 800 miles f r o m
t h o s e w i t h s u b m e t r a c e n t r i c X c h r o m o s o m e . Since t h e
d e t a i l e d k a r y o t y p i c d a t a of t h e o t h e r t w o species of
Bandicota 8,4, s t u d i e d b y m o d e r n t e c h n i q u e , are n o t
a v a i l a b l e it is n o t possible t o c o m p a r e t h e k a r y o t y p e of
B. b. be,~galensis r e p o r t e d in t h i s p a p e r .
A t p r e s e n t , it is v e r y difficult to s p e c u l a t e t h e direction
of c h a n g e in t h e m o r p h o l o g y of t h e X c h r o m o s o m e s in
t h e s e p o p u l a t i o n s . T h e X c h r o m o s o m e e q u a t i o n , SM
A could be reversible. E x a m i n a t i o n of a d d i t i o n a l specim e n s m a y reveal f u r t h e r course of X c h r o m o s o m e
v a r i a t i o n , if any, in t h i s subspecies 10.
Rdsumd. Des p r 6 p a r a t i o n s de mo~lle osseuse o n t p e r m i s
d ' 6 t a b l i r le m o m b r e diploide (2N = 42) et le n o m b r e
f o n d a m e n t a l (NF = 52) de Bandicota b. bengalensis
(Gray), les sp6cimens. 6tudi6s a p p a r t e m e n t 5, trois p o p u -
lations d i s t i n c t e s (Rohru, Varanasi, Belonia, Indes).
Le n o m b r e e t la f o r m e des a u t o s o m e s s o n t les m ~ m e s
d a n s les t r o i s 6chantillons alors que I ' X p e u t ~tre acroc e n t r i q u e ou s u b m 6 t a c e n t r i q u e ; L ' Y est p e t i t et subm6tacentrique.
S. PATHAK 11
Cytogenetics Laboratory, Department o/Zoology,
Banaras Hindu University,
Varanasi-5 (India), 29 July 7977.
10 Supported by the University Grants Commission, India, and a
grant from the Ford Foundation, USA, to Prof. Dr. S. P. RAYCHAUDHURI.The author is thankful to Dr. V. S. AGRAWALof the
Zoological Survey of India, Calcutta, and Mr. S. M, KULKARNIOf
the Virus Research Centre, Poona, for providing and identifying
the specimens. The editorial assistance of L.C. ELL~TT is also
appreciated.
n Present address: Cytogenetics Laboratory, Texas Children's
Hospital, Baylor College of Medicine, Texas Medical Center,
Houston (Texas 77025, USA).
Second Discovery of Multiple Sex C h r o m o s o m e s A m o n g Fishes
The v i v i p a r o u s fishes of t h e f a m i l y Goodeidae (suborder
C y p r i n o d o n t o i d e a ) are c o n f i n e d t o Mexico. T h e i r c h r o m o s o m e n u m b e r a n d some facets of t h e i r biology a n d classif i c a t i o n were r e c e n t l y s u m m a r i z e d b y MILLER a n d FITZSIMONS1, w h o i n c l u d e d t h e first k a r y o t y p e for t h e family.
T h e y n o t e d t h a t t h e c h r o m o s o m e n u m b e r varies f r o m 24
t o 48 in 35 (of p e r h a p s 38) species. N o n e of t h e s e species
s h o w e d a n y d e t e c t a b l e differences b e t w e e n t h e sexes in
c h r o m o s o m e n u m b e r or form. H o w e v e r , one u n d e s c r i b e d
genus, s u b s e q u e n t l y k a r y o t y p e d , a p p e a r s to be u n i q u e for
t h i s f a m i l i y in h a v i n g a diploid n u m b e r of 42 in t h e female
a n d 41 in t h e male. Like t h e genus of a r e l a t e d g r o u p (the
C y p r i n o d o n t i d a e ) w i t h 2n = 48 in t h e female a n d 2n = 47
in t h e male 2, t h i s species is k n o w n only f r o m a single
d r a i n a g e b a s i n in Mexico.
I n o r d e r to o b t a i n t h e c h r o m o s o m e figures gill e p i t h e l i u m w a s used, following t h e m e t h o d of MCPHAIL a n d
JONES 8 w i t h s o m e m o d i f i c a t i o n s 4. 60 cells of 4 females a n d
60 cells of 5 males were observed. Several pieces of testis
tissue were s q u a s h e d to o b t a i n m e i o t i c figures.
T h e female k a r y o t y p e h a s a d i p l o i d n u m b e r of 42 including 6 large m e t a c e n t r i c s , 2 s m a l l m e t a c e n t r i c s , 2 small
1 R. R. MILLERand J. M. FITZSIMONS,Copeia I, 1 (1971).
T. UYENO and R. R. MILLER,Nature, Lond. 231,452 (1971).
8 j. D. McPHAxL and R. L. JoNEs, J. Fish. Res. Board, Canada 23,
767 (1966).
4 R. BEAMISH,Ph.D. thesis, Dept. ZooL, Univ. of Toronto 1970.
224
Specialia
EXPERIENTIA 28/2
Figs. 1 and 2. Karyotype of the unnamed Mexican goodeid fish : female above,
male below. Scale (in all figures) is 5
[LFn.
s u b m e t a c e n t r i c s or s u b t e l o c e n t r i c s , 2 m e d i u m - s i z e d subt e l o c e n t r i c s , a n d 30 a c r o c e n t r i c s of m e d i u m t o s m a l l size.
I n c o n t r a s t , t h e m a l e k a r y o t y p e i n v a r i a b l y possesses 41
c h r o m o s o m e s i n c l u d i n g 7 large m e t a c e n t r i c s , 2 small met a c e n t r i c s , 2 s m a l l s u b m e t a c e n t r i c s or s u b t e l o c e n t r i c s , 2
m e d i u m - s i z e d s u b t e l o c e n t r i c s , a n d 28 a c r o c e n t r i c s of med i u m t o s m a l l size. T h u s t h e m a l e has i m o r e large m e t a c e n t r i c c h r o m o s o m e a n d 2 fewer a c r o c e n t r i c c h r o m o s o m e s
t h a n t h e female (Figures 1-2). W e t h e r e f o r e c o n s i d e r
1 of t h e large m e t a e e n t r i c s in t h e m a l e k a r y o t y p e t o
be a Y c h r o m o s o m e a n d believe t h a t 2 of t h e a c r o c e n t r i c s
are p r o b a b l y X 1 a n d X 2 c h r o m o s o m e s ; in t h e f e m a l e karyot y p e , w e c o n s i d e r t h a t 4 a c r o c e n t r i c s of s i m i l a r size rep r e s e n t X I X ~ X = X 2 c h r o m o s o m e s , b e c a u s e t h e 2 a r m s of
t h e Y c h r o m o s o m e of t h e male, w h i c h r e p r e s e n t t h e original
Y a n d c o u n t e r p a r t of X 2, are of e q u a l length. T h e origin of
t h e m u l t i p l e sex c h r o m o s o m e s in t h i s species is p r o b a b l y
similar t o t h e case we r e p o r t e d earlier ~ a n d t o t h e process
s u g g e s t e d b y MATTHEY5 i n a r o d e n t , M u s m i n u t o i d e s
S m i t h . I n t h e t e s t i s squash, a t t h e diakinesis in meiosis,
t h e r e are 18 b i v a l e n t s , 3 q u a d r i v a l e n t s w h i c h r e p r e s e n t
large m e t a c e n t r i c s of t h e s o m a t i c m e t a p h a s e , a n d a t r i v a l e n t in w h i c h X~ a n d X~ c h r o m o s o m e s s e e m a t t a c h e d to
t h e Y c h r o m o s o m e in a n e n d - t o - e n d a s s o c i a t i o n (Figure 3).
If t h e m u l t i p l e sex c h r o m o s o m e s o r i g i n a t e d b y c e n t r i c
fusion of all a c r o c e n t r i c a u t o s o m e w i t h t h e a c r o c e n t r i c sex
c h r o m o s o m e , w h i c h was o t h e r w i s e i n d i s t i n g u i s h a b l e , w e
suspect that other species of the family Goodeidae also
Fig. 3. Diakinesis in emiosis of the unnamed goodeid, prepared by
testis squash; the arrow indicates the sex trivalent.
5 R. MATTHEY,Chromosoma 16, 35 (1965}.
15.2. 1972
225
Speeialia
Fig. 4. Somatic chromosomes at metaphase of 2 goodeid fishes:'A) Hubbsina turneri 2n=48, and B) Characodon lateralis 2n-24.
h a v e X Y chromosomes t h o u g h t h e y are similar and undetectable b y present techniques.
A m o n g the k a r y o t y p e s of goodeid fishes, Hubbsina turneri de B u e n has the simplest pattern, w i t h 48 aeroeentric
chromosomes in b o t h sexes (Figure 4a). The species w i t h
the most derived k a r y o t y p e is Characodon lateralis Gtinther, which has 24 large metacentrics (Figure 4b) plausibly
formed b y R o b e r t s o n i a n fusions. Other goodeid species
h a v e k a r y o t y p e s comprising various p a t t e r n s and diploid
numbers t h a t are often reduced b y centric fusions.
The ancestral k a r y o t y p e of the species reported here
p r o b a b l y had 48 chromosomes, as in the m a j o r i t y of species in the Goodeidae (26 a m o n g 38 examined). The diploid n u m b e r was subsequently reduced b y successive
R o b e r t s o n i a n fusions, as in some other goodeids. B u t the
i n v o l v e m e n t of t h e Y chromosome in t h e fusion w i t h an
a u t o s o m e produced t h e multiple sex chromosome system
so far unique in this family, and only the second k n o w n
e x a m p l e a m o n g fishes.
The 2 species, 1 in t h e family Cyprinodontidae and 1 in
the Goodeidae, which were found to possess m u l t i p l e sex
chromosomes h a v e several features in c o m m o n : 1. b o t h
species h a v e a v e r y limited distribution and are localized
as small populations ; 2. b o t h are small and exhibit distinct
sexual d i m o r p h i s m ; 3. b o t h species belong to the suborder
C y p r i n o d o n t o i d e a ; 4. b o t h families representing these 2
fishes h a v e species in which t h e k a r y o t y p e s include large
metacentrics derived b y R o b e r t s o n i a n fusions; 5. b o t h
live in Mexico ; and 6. b o t h species possess unique morphological characters a m o n g t h e species in their respective
families (to be described elsewhere).
The specimens used in this s t u d y are preserved in the
collections of the Museum of Zoology, U n i v e r s i t y of Michigan e.
Zusammen/assung. Bei einer bisher nicht beschriebenen
m e x i k a n i s c h e n Fischart werden 41 A u t o s o m e n beim
M/innchen und 42 b e i m W e i b c h e n gefunden. Die Befunde
spreehen fiir ein S y s t e m m u l t i p l e r S e x u a l c h r o m o s o m e n
dieser Fische.
T. UYENO
7 and
R. R. MILLER
Museum o/Zoology, The University el Michigan,
A n n Arbor (Michigan 48104, USA),
16 August 1971.
s This research was supported by the U.S. National Science Foundation grant No. GB 14871 to R. R. MILLER,and No. GB 8212 to the
Museum of Zoology (N. G. HAIRSTON),The University of Michigan.
v Present address: Nippon Luther Shingaku Daigaku, 3-10-20
Osawa, Mitaka, Tokyo (Japan).
N e w Evidence of a 3 8 - C h r o m o s o m e s Karyotype in South American Populations of the Roof Rat,
R a t t u s R a t t u s L. (Rodentia, Muridae)
I n previous issues of this periodical, the occurrence of
new cases of c h r o m o s o m e m u l t i f o r m i t y 1 in the species
Rattus rattus has been described 2,8. The known ' n o r m a l '
k a r y o t y p e of this wide-sprea d and highly p o l y t y p i c
E u r a s i a t i c species was reported by several authors *-e to
be composed of 42 chromosomes, a m o n g which no pair
of large m e t a c e n t r i c s is present. This k a r y o t y p e was
studied f r o m strains p r o b a b l y derived f r o m J a p a n e s e and
E u r o p e a n populations. More recently, it was confirmed in
wild Rattus rattus from J a p a n , Formosa, Thailand, Philipines, J a v a and Celebes 7, as well as f r o m I n d i a s.
Disagreements w i t h these results were reported earlier
for strains from N o r t h A m e r i c a 0,1~ of the same species,
which showed 40 chromosomes, and later b y the occurrence
o f m o n o m o r p h i c populations w i t h 38 chromosomes cornprizing 2 large metacentrics in p o p u l a t i o n s from A r g e n t i n a
and Brasil~, n and in island and inland populations f r o m
Tuscany, I t a l y 3. Similar m o n o m o r p h i c 2n = 38 forms