GENETICS OF FISH 



399 



This diagram illustrates the peculiar way in which the spotted (Sp) pattern is inherited. The 

 female is represented by the formula W Z while the male is Z Z. The spotted factor is asso- 

 ciated with sex. When the spotted platy is the male parent (Zsp Zsp) and a non-spotted platy 

 is the female parent (Wsp Zsp), all the offspring of the mating, both the sons and daughters, 

 are spotted like their father. When the spotted individuals of the first generation (F, ) are 

 mated together, brother to sister, the ratio of three spotted platyfishes to one non-spotted is 

 obtained in the second generation (F2). Up to this point the results of this mating resemble 

 the inheritance of the stippling factor, but note the following significant fact: all the non- 

 spotted fishes obtained in the second generation are females. And the spotted platyfishes 

 contain both males and females, but there are two spotted sons to every non-spotted daughter. 

 This is an example of the inheritance of a sex-linked heritable factor. A similar type of in- 

 heritance is found in birds and moths for certain characters. 



Xiphophorus hrllerii mother 



Vij'hopliotiti hrllrrii mother 



Xiphopliorus hcMerii mother 



Xipliophonw helleril mother 



X 



X 



X 



X 



PUlypopcllu* falhrr 

 Cold pl«l|r 



Red-finned pUlyhcIleri hyhtH 



S?i 



PlslypoecUu* filhn 

 Red pUtr 



'%?*• 



Plitypoecilua father 

 Black pUty 



Black plalr-hcllerl hrbrid 



Platjrpoecilua father 

 Stippled aod Spoiled platr 



Mottled pUty-helleri hyhrid 



The platyfishes and the Mexican swordtail will readily hybridize. The hybrids are 

 classified according to the original varieties of the species used in the cross. The 

 gold platy and the swordtail produce the red finned platy-helleri hybrid. The red 

 platy and the swordtail produce the red platy-helleri hybrid. The black platy and 

 the swordtail produce the block platy-helleri hybrid. The stippled and spotted 

 platy and the swordtail produce the mottled platy-helleri hybrid. These hybrids 

 frequently develop the neoplastic disease known as melanosis. 



