QUESTION 13 You are working on a question found in your textbook. This question

Question

QUESTION 13

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)

Please provide detailed explanation.

Explanation / Answer

A) Individual III-4 is a female. Female contains two X chromosomes. One of the X chromosome comes from mother and the other comes from the father. Father (II-3) should be affected, but he is normal. So, if the trait is inherited as X linked recessive, it is impossible for individual III-4 to express the trait.

B) The correct mode of inheritance is autosomal recessive. Because, there is alteration of generations in the affected trait. The trait is expressed only in homozygous state.

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