Question

Given below is a pedigree chart with symbols for sex-linked trait in humans. The trait of the pedigree chart is?

A) Recessive Y-linked
B) Recessive X-linked
C) Dominant Y-linked
D) Dominant X-linked

Answer 1

Hint:In human genetics, the pedigree analysis is an important tool that is used to study the inheritance of a particular trait, abnormality or disorder. By pedigree analysis, it is easier to identify whether the trait in question is dominant or recessive.

Complete answer:
The analysis of characteristics in many generations of a family is known as pedigree analysis. The inheritance of a single characteristic over centuries is reflected in the family tree in the pedigree analysis. Pedigrees use a common collection of symbols to make them easy to recognise. Males are depicted in squares, while females are represented in circles. Parents are linked by horizontal lines, while vertical lines originating from horizontal lines correspond to symbols for their children.
X-linked diseases are characterised by expression in both genders, but with a higher prevalence in females due to a higher number of X-chromosomes. The trait given in the pedigree is dominant X-linked. The male is affected in the first generation, but the female is not affected. Both females are affected in the second generation, and none of the males are affected. This indicates that the X-linked trait is dominant. In the third generation, all male and female offspring of a single X-linked trait are affected in the cross between the affected female and the unaffected male. Thus, a positive father would pass the disease to all his daughters, but not to his sons, while a positive female would pass the trait to half of his sons and half of his daughters.

Thus, the correct answer is option D i.e., Dominant X-linked

Note:A genetic trait is considered dominant if it is expressed in a person who has only a single copy of that gene. A recessive trait is expressed only when two copies of the genes are present.