Inheritance of body and peritoneum color in hybrids of Oreochromis aureus and red O-niloticus

Segregation of body and peritoneum pigmentation was studied in three develo pmental stages in F2 hybrids and progeny of F1 hybrids backcrossed with par ents Oreochromis aureus (black body and peritoneum) and red O. niloticus(re d body and white peritoneum). Segregation in adult F2 hybrids corroborated previous findings that red bod y color is dominant over black and controlled by a single gene (R). Results further showed that (a) the colors of the body and of the lower-posterior part of the peritoneum are strongly associated (p<0.001) and explained by t he interaction between two separate genes; (b) the color inheritance of the upper-anterior part of the peritoneum could not be explained by a simple d ominant-recessive mechanism. The analysis of color inheritance in adult hybrids resulted in a non-Mendel ian segregation of the peritoneum and body pigmentations. Our data showed t hat this segregation was the result of selective mortality among albinos st arting in 4-day embryos. Genuine segregation results were obtained only whe n the color analysis was performed by microscopy in embryos before the age of four days. Embryo mortality is suggested to be due to incomplete homolog y between chromosomes derived from the closely related species used for hyb ridization.