21-27. Consider the pedigree below showing a rare (not commonly found in the pop
ID: 70679 • Letter: 2
Question
21-27. Consider the pedigree below showing a rare (not commonly found in the population) X- linked recessive trait. Assume no spontaneous mutations in this family and 100% penetrance. In the first generation, the man is unaffected and the woman is affected. Individuals indicated by letters in subsequent generations may or may not be affected. Choose your answer(s) carefully since you will receive credit only if you select all possible correct answers.
21. Which individuals, if any, must be affected? If none of the individuals would be affected for sure, then select “Q”
Q
22. Which individuals, if any, should be carriers of this trait, but not affected (100% chance of being carriers)? If none of the individuals has a 100% chance of being a carrier, then select “Q”.
Q
23. Select all individuals, if any, who have a 1?2 chance of being carriers of this trait. If none of the individuals have a 1?2 chance of being a carrier, then select “Q”.
Q
24. If individual A also showed the trait (was shaded in), which of his children would for sure be affected? If none of the individuals would be affected for sure select “Q”.
Q
A O (PExplanation / Answer
In sex linked or X-linked diseases, the defective allele is present in X-chromosome. X- linked diseases could be developed in females only when they inherit two X-linked recessive alleles, one from the mother and another from the father. Whereas in males, presence of only one defective allele will result in expression of disease phenotype. Haemophilia is an example of X-linked disease in which females act as carriers and males are generally affected.
In the given example, the mother is affected, so both C and E must be affected because they inherit defective X-allele from their mother. B is the carrier; she inherits one defective allele from her mother. So, the male offspring of B namely G and I might be affected if they inherit the defective gene.
Thus the correct options are, C and E must be affected, G and I might be affected.
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