It is exceedingly difficult to determine the sex of very you

It is exceedingly difficult to determine the sex of very young chickens, but it is easy to tell, by visual observation, whether the feathers are \"barred\". The barred pattern is inherited as a sex-linked dominant trait.. This trait is used regularly by chicken breeders who receive orders for only male or female chicks, and must be able to deliver the appropriate sex of very young birds. Note that in birds, sex is determined as follows: XX = male, XO = female; only the X chromosome carries sex- linked genes.) You need to deliver young female chicks to a farmhouse. You currently have 2 breeding lines going. The first lines are crosses from a normal rooster and a barred female, while the second lines are crosses from a barred rooster and a normal female. From which cross (Line #1 or Line #2) can you guarantee the delivery of only females? In other words, with which cross will it be possible to accurately tell the sex of the chicks, by feather pattern? What will the phenotypes be of these male and female chicks? Explain why the other line is not suitable for single-sex delivery.

Solution

During fertilization, one chromosome comes from one parent while the other chromosome comes from the other parent.

Therefore, to produce a female chick, ‘X’ should come from one parent while ‘O’ comes from another.

Since, ‘O’ is not present in male, it has to come from female parent. Therefore, ‘X’ comes from male parent.

Since the barred feathers is a sex-linked trait or X-linked trait, and the’ X’ chromosome should come from male parent, Line 1 would be more appropriate in selecting the young chick.

Line1:

Cross between normal rooster and barred female

The female has barred trait. Since the female has only one ‘X’ chromosome, barred trait is present on the same ‘X’ chromosome. This chromosome will be passed to all male progeny. Since it is a dominant trait, all males would shoew barred trait.

Female progeny of this cross would acquire ‘X’ chromosome from normal rooster and ‘O’ from barred female. Therefore, all the female would be normal.

Therefore, it is easy to select normal female from barred male.

Since it is a dominant trait, the barred rooster may be homozygous dominant or heterozygous dominant.

If it is homozygous dominant barred rooster, it will pass the barred ‘X’ chromosome to all its progeny (both male and female). We cannot distinguish female and male.

If it is heterozygous dominant, there is equal probability of passing barred trait containing ‘X’ chromosome to both male and female.

Differentiation cannot be done.