FOUNDATIONS FOR SEX 



51 



be phenotypically orange as the double dose, 

 0/0, covers up the effects of the other coat 

 color genes; or tortoiseshell, 0/+; or black 

 or tabby, +/+. The males may be orange, 

 '0/, black or tabby, +/, and the type unex- 

 pected tortoise. The tortoiseshell males are 

 timid, keep away from other males, and are 

 generally sterile. Testes are of much reduced 

 size and solid consistency. Exceptionally, 

 tortoiseshell males may mate and offspring 

 presumed from the matings may be born. 

 Active study of these males commenced as 

 early as 1904. Komai (1952) has offered a 

 unified hypothesis for their origin. Komai 

 and Ishihara (1956) have contributed added 

 information and a review of the literature 

 to which the reader is referred. 



The cat has 38 chromosomes including an 

 X-Y pair for the males. The tortoise males 

 agree in having this arrangement (Ishihara, 

 1956) , the X being 3 or 4 times the length of 

 the Y in all cytologic preparations from 

 Japanese cats. Komai (1952) visualizes the 

 cat X chromosomes as composed of a pairing 

 segment containing the kinetochore and gene 

 loci among which is that for the orange gene 

 and a differential segment, not found in the 

 Y chromosome, containing the factor-com- 

 plex for femaleness. The Y chromosome is 

 visualized as having a segment containing 

 the kinetochore and capable of pairing with 

 the X chromosome. This segment may cross 

 over with the X so that it may acquire the 

 locus for orange or its wild type. The Y 

 chromosome is viewed as containing two 

 differential segments. The one carrying the 

 factor complex for maleness is located to 

 correspond with the X differential segment 

 carrying the female sex factor. The second Y 

 differential segment is at the other end of the 

 chromosome and contains the male fertility 

 complex. The tortoiseshell sterile males are 

 interpreted as caused by a Y chromosome 

 crossing over with the X chromosome to in- 

 corporate the male segment and the gene 

 in the resulting Y chromosome but with the 

 loss of the male fertility segment. The gam- 

 ete carrying this modified Y fertilizing an 

 egg with a normal X chromosome containing 

 the wild type instead of the gene develops 

 into the sterile tortoiseshell male. The data 

 show that the probability of these events oc- 

 curring is small. Komai records as reliable 

 ■65 tortoiseshell male cats where the inci- 



dence of the O gene in the whole population 

 of Japanese cats is 25 to 40 per cent. Of the 

 65, 3 were apparently fertile. These cases 

 and the few others found in the literature are 

 regarded as caused by those rare occasions 

 when the Y chromosome incorporates the 

 gene but retains the male fertility complex 

 as might occur in double crossing over. The 

 hypothesized factor locations and crossing 

 over arrangements also may explain the un- 

 expected black females which are known to 

 occur in some matings. Although not men- 

 tioned, black males and orange males show- 

 ing the same sterility features as the sterile 

 tortoiseshell males should also be found in 

 the cat poi)ulation. If found they would 

 further strengthen the hypotheses. 



It is difficult to understand why, even with 

 its low initial frequency, the fertile tortoise- 

 shell male would not establish itself in the 

 Japanese cat population, inasmuch as they 

 are so admired and sought after by all the 

 people if any tortoiseshell males became as 

 fertile as the tortoiseshell male "lucifer" 

 (Bamber and Herdman, 1932) known to 

 have sired 56 kittens. 



Ishihara's work (1956) seems to close the 

 door on another attractive hypothesis to ex- 

 plain the origin of these unexpected cat 

 types. Tortoiseshell male reproductive or- 

 gans include small, firm testes showing re- 

 duced spermatogonial development. To- 

 gether with the interaction of the gene 

 with the wild type allele they suggest the 

 human types XXY + 2A which may arise 

 from nondisjunction. However, the chromo- 

 some type is shown to be XY -f- 2A = 38 

 which is fatal to this hypothesis. 



It is of interest that Komai in 1952 postu- 

 lated the male complex and fertility factors 

 in the Y chromosome of a mammal. The case 

 has a further parallel in the plant Melan- 

 drium in that the work of both Westergaard 

 (1946) and Warmke (1946) indicated the 

 Y chromosomes of this plant to contain such 

 factor complexes although in differing ar- 

 rangements. 



D. DEVIATE SEX TYPES IN 

 CATTLE AND SWINE 



As a caution in the mushrooming of cyto- 

 logic interjiretations of sex development, at- 

 tention may be directed to the freemartin 

 types known particularly from the work of 



