Question

From the pedigree below, determine the pattern of inheritance of the trait. Also determine the genotypes for all the individuals of generation I and generation II со оо 3 4 5 6 7 3 1 2 TTT Arial : 3 (12) T.E E Save All click Save Alert Click Save and Submiss and MacBook Air

Answer 1

In the case of generation 1 in the picture below, all three children (male and female) of the affected female parent and the unaffected male parent did not contract the disease. In the other scenario where the male parent is affected, one male offspring out of their 4 offsprings (male and female) is affected. This is not an X-linked inheritance, if it was the one male offspring out of the three offsprings in the first scenario would have the disease as he would have received the X chromosome from his affected mother. This condition is therefore, autosomal. Now, this cannot be a dominant trait , in which case half of the children would be affected.

In the first scenario, the dominant alleles are contributed by the father and therefore none of the children are affected. It is possible that the male parent is homozygous dominant for the trait whereas the affected female parent is homozygous recessive.  In the second scenario, the disease inheritance is 25% as one in four children is affected. Here the affected male parent is homozygous recesive and the female parent genotype has to be heterozygous so that one of the children is affected. This pattern of inheritance could therefore be autosomal recessive inheritance.

The dominant allele is represented as A and the recessive allele as a.

The genotype of the parents in generation 1 in the first scenario would be: aa for the affected female parent and AA for the unaffected male parent.

In the second scenario of generation 1, the genotype of the unaffected female parent is Aa and the affected male parent is aa.

In generation 2, since none of the three kids in the first scenario are affected, their genotypes are all heterozygous (Aa).

In the second scenario, the genotype of the affected male offspring would be aa and the unaffected male and female offsprings would be Aa.

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