Question

pedigree

8. The Addams family knows of three relatives who had Menkes disease, and X-linked recessive disorder in which a child does not grow, has brain degeneration, and dies by age two. Affected children have peculiar white stubby hair. Wanda Addams is hesitant about having children because her two sisters have each had sons who died from Menkes discase. Her mother had a brother who died of the condition, too. The pedigree for the family is shown below. A. Fill in the symbols for the family members who must be carriers of Menkes disease. B. What is the chance that Wanda (III-7) is a carrier? C. If Wanda is a carrier, what is the chance that a son of hers would inherit the disease? D. Why don't any women in the family have Menkes discase? 3 6 5 IV Menkes disease

Answer 1

A.

Menkes olisease 11 2xy xay Wanda 7 |2 4 3 4 56 Xay xay wanda Parcents ax (1-3) y (-2) X Y - cauer 114-25/. xax - deceased 7- 4-25/. ay 14-25. mmal t - XX /4-25 Y OR

B. Out of 4 children, chances that Wanda is a carrier, are 25%. But if we take only female children into consideration, than there are 50% chances of Wanda being a carrier. (Shown in the figure above).

C. If Wanda is a carrier, X^aX, then she will produce two gametes, X^a and X, each with an equal probability of 50%. We know that a son inherits X chromosome from his mother and Y from his father. So, Wanda's son can be either X^aY (affected) or XY (normal), both genotypes with an equal probability of 50%.

D. This is because, women have 2 copies of X chromosomes and males are hemizygous for X. Any recessive mutation would affect males more than females because one mutated X chromosome is enough in males to cause disease whereas, 2 mutated X chromosomes are required to cause disease in females. This is possible only when the father of a female is has X linked recessive disorder and her mother is atleast carrier. This seems to be very unlikely. Hence, females are not seen to be affected in this case.

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