This is a diagram of sex-linked inheritance using a male Grey and a female CFW. Sex-linked inheritance is a slightly more complicated than recessive traits, but it is not difficult to understand. In sex-linked genes, only males can be split. Females cannot be split for sex-linked traits. In sex-linked traits females always show the color that they are. They cannon conceal a sex-linked gene as the males can. The sex chromosomes in birds are the opposite of that in humans. Human males are XY, females are XX, in birds males are ZZ and females are ZW. The "W" is the sex determining chromosome just as the Y is in humans. A bird with a W is always a female. In this cross, capital letter Z = Grey; small letter z = CFW. Hence, ZW = Grey hen & zW = CFW hen. ZZ = Grey Male; zz = CFW male.

Follow the red and blue arrows to see how the genes are inherited from parent to offspring. Remember offspring receives one sex chromosome from each parent. Females contribute Z's and W's, males contribute only Z's. In the F1 above all of the offspring are Grey. The males are splits for CFW, but not the hens. In the F2 cross, we use the original CFW hen since the daughters do not carry the CFW gene. By using the CFW hen mated to her son which is split for CFW, the results of the second cross will produce 50% Greys and 50% CFW. If we had used the daughters instead of the CFW hen, we would have produced only CFW hens, and no CFW males.

Sex-linked Inheritance using a Male Zebra

with the trait.

This is a diagram of sex-linked inheritance using a CFW male and a Grey female. Notice that in the first generation results we produce CFW females. This genetic behavior occurs in all sex-linked varieties. Because the male CFW contributed small "z" to the female offspring and zW = CFW hen. The same would happen in Fawns, and Lightback Zebras. Notice that all of the first generation males are splits for CFW (Zz). When we interbreed these offspring in the second cross, Zz X zW, we produce a 50:50 ratio of CFW and Grey, as we observed in the previous cross.


These plates and information are from my book, Varieties and Genetics of the Zebra Finch.