The pedigree below tracks Duchenne Muscular Dystrophy (DMD) through several generations. DMD is an X-linked recessive trait.

If individuals I-1 and I-2 had another son, what is the chance that he would have DMD?

Choose 1

(choice A)
A
0%

(choice B)
B
25%

(choice C)
C
50%

(choice D)
D
100%

25%

Explanation:

When looking at a pedigree remember that:

squares are malescircles are femalesthe solid colored figure represents an individual affected by a diseasethe empty figure represents a healthy individual

Let us assign the symbol X⁺ to represent the dominant allele linked to the X-chromosome and expressing healthiness, and X⁻ to represent the recessive allele expressing the dissease.

According to this pedigree

I1 is a man affected by the disease, YX⁻I2 is a healthy woman X⁺X⁻we can see that among the progeny (generation II) there are two individuals affected (a boy and a girl) and one healthy girl. This means that the mother I2 is heterozygous for the trait.

So, having their genotypes we can know what are the probabilities of getting a son with DMD

Parentals)    YX⁻     x     X⁺X⁻  

Gametes)   Y     X⁻      X⁺     X⁻

Punnett square)

                        X⁺             X⁻

            X⁻      X⁺X⁻         X⁻X⁻    

            Y        X⁺Y           X⁻Y

F1)

The probabilities of getting a healthy daughter X⁺X⁻ are 25%The probabilities of getting a healthy son X⁺Y are 25%The probabilities of getting a daughter with DMD X⁻X⁻ are 25%The probabilities of getting a son with DMD X⁻Y are 25%

Ithink its c hope it : )

Because people are wasting it