This pedigree below shows the inheritance of a very rare trait. Answer the quest

Question

This pedigree below shows the inheritance of a very rare trait. Answer the questions a. Assume that the inherited disorder has no new mutations arising, what modes of inheritance is/are consistent with this pedigree? (Choices: X-linked dominant, X-linked recessive, Autosomal dominant, Autosomal recessive, Y-linked) b. For each consistent mode of inheritance what is the probability that individuals 1 & 2 (IV-3 & IV-4) will have i. an affected son ii. an affected daughter iii. an unaffected son iv. an unaffected daughter

Explanation / Answer

a) This is X-linked recessive inheritance, because probability of having disease is 50% more in male.

So here I-2 is XaY which is recessive but as only 1 X is present in male, male will be diseased. Similarly, III-3 will also have XaY.

b) There are two conditions. One is IV-3 (XY) x IV-4 (XXa)

(i) The probability of having an affected son is 1/4.

(ii) The probability of having an affected daughter is 0.

(iii) The probability of having an unaffected son is 1/4.

(iv) The probability of having an unaffected daughter is 1/4.

Another is IV-3 (XY) x IV-4 (XX)

(i) The probability of having an affected son is 0.

(ii) The probability of having an affected daughter is 0.

(iii) The probability of having an unaffected son is 1/2.

(iv) The probability of having an unaffected daughter is 1/2.

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