In hens (female chickens), only one gonad develops into an ovary; the other rema
ID: 57048 • Letter: I
Question
In hens (female chickens), only one gonad develops into an ovary; the other remains undeveloped in a more-or-less embryonic state. Spontaneous and experimentally induced sex reversals have been reported wherein the ovary degenerates and the embryonic gonad develops into a testis or ovitestis capable of sperm production. Reports of such sex-reversed chickens (which look and act like roosters) actually reproducing as roosters have not been substantiated, but let’s imagine this is possible. Suppose a Z-linked recessive allele causes excessively long tail feathers (recall that in birds the female is the heterogametic sex). A female chick whose father had long tail feathers is experimentally altered so that “she” develops into a rooster. “He” is now mated to a hen with normal tail feathers. What kinds of offspring and in what ratios do you expect from such an unusual cross? Consider both the phenotype and the sex of the offspring and assume that WW is lethal in early cleavage stages of embryonic development.
Explanation / Answer
This unusual cross produces offsprings having long tail feathers with the expected ratio of 1:1
As the chick having Z-linked recessive trait is altered to a rooster, it will have two Z-lined recessive genes to express the long tail feathers.
Short tail feathers are dominant traits present in the hen that mated to the altered rooster.
Observe the below cross for understanding:
There are two types of phenotypes: Long tailed feathers, and short tailed feathers.
The sex ratio is 1:1