Question

In: Biology

A normal man marries an affected woman with an X-linked recessive disease. The expected genotypes of...

A normal man marries an affected woman with an X-linked recessive disease. The expected genotypes of their offspring are_________.

Expert Solution

In an X- linked disease, the abnormal alelle is present at the X-chromosome. Since it is recessive, both the alleles of that particular gene has to be affected for the disease to be manifested.

Let the abnormal allele be represented by x'. And X is the normal allele.

We know, the chromosome pattern in a male is XY and female is XX.

Since females have 2 copies of the X chromosomes, both the alleles should be affected (x') for the disease to be manifested. Females with one affected allele will be carriers.

XX - Normal female;... x'x' - Affected female;...Xx' - Carrier female

Whereas, males have a single X chromosome. When this is affected (x') the disease is manifested. So, there is no carrier state in males.

XY - Normal male;... x'Y - Affected male;...No carrier male

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Here, cross is between a normal man (XY) and an affected woman (x'x')

The gametes will be :

The Punnet square is :

x	X	Y
x'	Xx'	x'Y
x'	Xx'	x'Y

The genotypes of the offsprings will be 2 / 4 Xx' : 2 / 4 x'Y

i.e 50 % Xx' : 50 % x'Y

So, All the female offsprings will be carriers (Xx') and all the male offsprings will be affected (x'Y).

gladiator answered 2 years ago

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