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

Question

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 lII-4 cannot express the trait if the mode of inheritance is X-linked recessive 4 5 7 8 10 IV Answer the following questions. (a) Explain why it is impossible for individual lI-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 IlI-4 but the entire pedigree. Give specific examples. (3 marks)

Explanation / Answer

a. The given pedigree does not follow an X-linked recessive inheritance pattern. This is because if III-4 has to show the mutant phenotype, both of her parents must carry at least one recessive allele. If her father carries a recessive allele, he would show the phenotype. But, from the pedigree, it is clear that the father, II-3 is unaffected.

b. The given pedigree follows autosomal recessive inheritance pattern

Reasons:

i. Unaffected parents have affected progeny. So, it is a recessive mutation.

ii. An affected female, III-4 is produced to unaffected parents, II-2 and II-3. So, it is an autosomal mutation.

Examples for autosomal recessive disorders: Cystic fibrosis and Phenyl ketoneuria

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