Question

Some types of muscular dystrophy are X-linked recessive disorders. A mother who is a carrier for muscular dystrophy has children with a father who doesn’t have muscular dystrophy.
a. What percentage of their sons will have the disease, and what percentage of their sons will be carriers?
b. What percentage of their daughters will have the disease, and what percentage of their daughters will be carriers?

Show your work with a Punnett Square, using XD to represent the allele not associated with muscular dystrophy and Xd to represent the allele associated with muscular dystrophy. You can copy/paste the blank table below or create a table in the submission box to complete the Punnett square.

Answer 1

D gene is an X-chromosome-linked gene. a) 100% will have the disease, XdY // 0% will be carriers. b) 0% will have the disease // 100% will be carriers, XDXd.

What are the séx-linked genes?

These are genes that can be found only in the X-chromosome. The inheritance pattern expressed by these genes varies from the one expressed by genes located in autosomal chromosomes.

In the exposed exampe,

- muscular dystrophy are X-linked recessive disorders

- woman ⇒ carrier for muscular dystrophy ⇒ heter0zyg0us ⇒ XDXd

- man ⇒ doesn’t have muscular dystrophy ⇒ X-chromosome with the dominant allele ⇒ XDY

- XD ⇒ chromosome rarrying the dominant allele

- Xd ⇒ chromosomes carrying the recessive allele

Cross: Man x Woman

Parentals)   XDY     x      XDXd

Gametes) XD   Y           XD   Xd

Punnett square)       XD           Xd

                      XD   XDXd       XDXd

                      Y      XdY           XdY

F1) 1/2 = 50% of the progeny will express the normal phenotype,  XD-

    1/2 = 50% of the progeny will have muscular dystrophy, Xd-

    100% of the girls will be normal and carriers,  XDXd

    100% of the boys have muscular dystrophy, XdY

a. What percentage of their sons will have the disease, and what percentage of their sons will be carriers?

Considering only boys,

• 100% of them will have the disease, XdY
• 0% will be carriers.

b. What percentage of their daughters will have the disease, and what percentage of their daughters will be carriers?

Considering only girls,

• 0% of them will have the disease,
• 100% will be carriers, XDXd

You will elarn more about séx-linked genes at

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