144 



SCIENCE 



[N. S. Vol. XXXVI. No. 918 



DISCUSSION AND COBBESPONDENCE 



SEX-LIMITED INHERITANCE IN CATS 



To THE Editor of Science: In Science for 

 May 17, Mr. C. C. Little, under the title 

 " Preliminary Note on the Occurrence of a 

 Sex-limited Character in Cats," describes first 

 results from the mating black female by yel- 

 low male, and concludes that the black and 

 yellow factors are sex-limited in the male cat. 

 For some years I have been collecting evi- 

 dence on this question, and have recently be- 

 gun breeding experiments, the first litters 

 from which are expected very shortly. From 

 evidence which I have obtained from breeders, 

 and which I propose to publish when my own 

 experiments are sufficiently advanced to pro- 

 vide adequate comparison, I have no doubt 

 that Mr. Little is correct in supposing that 

 the male cat shows sex-limited transmission 

 of a color-factor. That this is so has been 

 clear to me for two years or more, and I wel- 

 come Mr. Little's further evidence in the 

 same direction. My data, including records 

 of from 30 to 80 kittens in each of the pos- 

 sible crosses between black, orange and tor- 

 toise, do not, however, entirely confirm the 

 hypothesis which he suggests. I have evidence, 

 from a breeder who is thoroughly reliable, 

 that occasional black (or blue) females are pro- 

 duced from the cross black female X yellow 

 male, and also from tortoise female X yellow 

 male. That such black females are unusual 

 is quite certain, and it is of the greatest im- 

 portance to determine under what circum- 

 stances they occur. Their existence would 

 seem to indicate that the sex-limitation is not 

 absolute, but partial, as in the case of gametic 

 coupling between members of distinct Men- 

 delian pairs. 



Mr. Little, if I understand him, assumes 

 that both black and yellow factors are sex- 

 limited in the male cat. I think a more prob- 

 able assumption is that all gametes bear the 

 factor for black, which appears to be hypo- 

 static (recessive) to all other colors, and that 

 the yellow female is homozygous, the yellow 

 male and tortoise female both heterozygous 

 for the yellow factor. Using the terminology 

 X = male, XX = female, Y = yellow, y its 



absence, B = black ; and supposing that Y is 

 closely, if not invariably coupled with X in 

 the male, we have 

 Yellow male =XTyBB, producing gametes 



XYB, yB; 

 Yellow female ^=XX'£¥BB, producing gametes 



XTB; 

 Tortoise tema.\e=^XYyBB, producing gametes 



X¥B, XyB. 



Yellow is normally completely dominant 

 (epistatic) over black in the male, only par- 

 tially so when heterozygous in the female, 

 giving tortoise. It is possible that the excep- 

 tional tortoise-shell males are the correlative 

 of the exceptional black females from yellow 

 sires. If the coupling between the sex-factor 

 X and the yellow factor Y is occasionally 

 broken, then Y, transmitted from a male 

 parent apart from X might perhaps behave 

 difiFerently from Y coupled with X, and pro- 

 duce a tortoise instead of a yellow male. 

 Until further data are available, however, 

 this kind of speculation is of little value. 

 My main object at present is to point out that 

 the complete solution of the problem requires 

 large numbers of observations, so that we may 

 know not only what exceptional conditions 

 are possible, but also the frequency and mode 

 of their occurrence. My own experiments 

 are unavoidably on a small scale, and with 

 regard to data derived from breeders, it is 

 notoriously difficult to avoid all chance of 

 mistake unless the cats are kept in cages, a 

 precaution not always taken by the amateur. 

 It is therefore very desirable that further ex- 

 periments should be done on a large scale, 

 under absolutely trustworthy conditions. 



l. doncaster 

 Cambridge, England, 

 May 28, 1912 



" TERMS USED TO DENOTE THE ABUNDANCE OR 

 RARITY OP BIRDS " ' 



The paper under this title in a recent issue 

 of Science seems to be another attempt to 

 replace spontaneous choice by labored precept, 



• Kuser, J. D., Science, N. S., Vol. XXXV., No. 

 911, Juue 14, 1912, pp. 930-931, chiefly a reprint 

 from ' ' The Birds of Somerset Hills, ' ' Rahway, 

 N. J., 1912, pp. 128-132. 



