Q 10. You are working on a question found in your textbook. This question states

Question

Q 10. You are working on a question found in your textbook. This question states that the following pedigree is for a trait that shows X-linked recessive inheritance.

Using this information, you begin to assign the genotypes to each member in this pedigree, however, you soon realize that the textbook has made a mistake. For example, individual III-4 cannot express the trait if the mode of inheritance is X-linked recessive.

Answer the following questions.

(a) Explain why it is impossible for individual III-4 to express the trait if the inheritance is X-linked recessive. (2 marks)

  

(b) What would you conclude is the correct mode of inheritance for this pedigree? Explain how this type of inheritance accurately explains the result of not only individual III-4 but the entire pedigree. Give specific examples. (3 marks)

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- Q 9S E Z 08 0 0 DLO. ? ?? " III

Explanation / Answer

A. Because if it is X-linked inheritance, I-1 has Xa / Y and I-2 has XA / XA. (A - Dominant : a - Recessive)
So, II-2 is XA / Xa (Normal and heterozygous)
Then III-4 is XA / Xa or XA / XA (Normal).
It not have a possible to make disease in III-4 if it is X-linked recessive disorder.

B. Autosomal recessive disorder
Appears in both sexes with equal frequency.
Trait tend to skip generations
Affected offspring are usually born to unaffected parents

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