You are working on a question found in your textbook. This question states that
ID: 132595 • Letter: Y
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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 lI-4 cannot express the trait if the mode of inheritance is X-linked recessive. IV Answer the following questions. (a) Explain why it is impossible for individual lIl-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)Explanation / Answer
Answer 1: According to the information, the disease is inherited in X-linked recessive manner in the pedigree. This means that a female must be homozygous and a male must carry a single copy of affected X-chromosome in order to have the disease. Based upon this information, it can be seen that the individual III-4 can be affected by the disease only under one condition. This suggests that the father of this individual must be affected by the disease and the mother should be at least a carrier of the chromosome. Since the pedigree displays that the father is normal, this individual cannot be affected by the disease.
Answer 2: Since the disease is not following X-linked recessive manner of inheritance, it is very likely that it is inherited in autosomal recessive manner. For example, the parents of individual III-3 need not be affected by the disease yet this individual is affected only if both the parents are autosomal carriers of the affected allele. This holds true for all the pedigree in this family.
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