THE TORTOISESHELL CAT 



F. A. Hays 

 Massachitscits Agricultural College 



GENETICISTS are almost uni- 

 versally agreed on the follow- 

 ing" points regarding color in- 

 heritance in cats : 



1. That black males mated to yel- 

 low females give tortoise females 

 and yellow males. 



2. That yellow males mated to 

 black females give tortoise fe- 

 males, an occasional black fe- 

 male, and all black males. 



3. That black males mated to tor- 

 toise females give both tortoise 

 and black females and both yel- 

 low and black males. 



4. That yellow males mated to tor- 

 toise females give both yellow 

 and tortoise females, an occa- 

 sional black female, and both 

 yellow and black males. 



A few tortoise males have been re- 

 corded. Such males are considered 

 sterile. The two most important ques- 

 tions in this connection are : 



1. \\'hy are tortoise males not of 

 frecpent occurrence? 



2. Why are tortoise males sterile? 



The first of these questions may be 

 elucidated by a brief statement of the 

 method of inheritance of the factors 

 for black and yellow, which when to- 

 gether make the tortoise pattern. The 

 results of the four types of matings 

 enumerated above clearly place the 

 two factors for coat color in the cate- 

 gorv of sex-linked factors as Little"* 

 suggests. In such case the male prog- 

 env receive an X-chromosome from 



their dam carrying either the gene for 

 black or yellow color. This chromo- 

 some is paired with the Y-chromo- 

 some from the sire. This assumedf 

 Y-chromosome is apparently devoid 

 of genes for the colors in questions so 

 that the sons inherit their color only 

 from their dams. Daughters receive 

 an X-chromosome from both sire and 

 dam and thus provide a mechanism 

 for both the black and the yellow fac- 

 tor to occur in the female zvgotes. 

 The combined action of these factors 

 gives the tortoise pattern. 



Different concepts of the possible 

 explanation for the occurrence of a 

 few tortoise males need not be dis- 

 cussed. The sterility in such males 

 has been explained by some as being 

 due to imperfect sex development or 

 to the partial transposition of the fe- 

 male to the male sex. Careful ex- 

 amination of the fetuses of seventy 

 pregnant cats by Doncaster and Bem- 

 ber^ has not revealed a single case of 

 confluence of blood vessels or fused 

 chorions. 



A means of explaining the infre- 

 quent occurrence of tortoise males and 

 their sterility, as well as the appear- 

 ance of the few unexpected black fe- 

 males in crosses 2 and 4, exists in the 

 crossing-over phenomenon. We may 

 assume that a cross-over only infre- 

 quently occurs between the X- and Y- 

 chromo somes of a yellow male be- 

 cause the genes occupy loci in very 

 close proximity, and moreover that 

 cross-overs sometimes take place in 

 the two X-chromosomes of females. 

 If a male with crossing-over between 



* For numbered references, see Literature Cited at end of article. 



t DeWinivarter has apparently discovered two types of spermatocytes in the cat, one 

 carrying seventeen and the other eighteen chromosomes. He ^was, however, unable to trace 

 the chromosomes farther than the spermatocyte stage. Because of the behavior of the colors 

 black and yellow in inheritance, we may be justified in assuming the existence of the Y 

 chromosome in half the spermatozoa until its absence is proven. 



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