Question

From the pedigree chart given below, identify if the trait is sex linked dominant or recessive.

• A. X-linked dominant
• B. X-linked recessive
• C. Y- linked
• D. X and Y- linked

Answer 1

The correct option is A X-linked dominant

From the pedigree chart, we see that the mother is affected, and father is unaffected. In the first generation 50 percent of the offsprings are affected (one son and one daughter). If the trait was due to a recessive gene on the X-chromosome, only sons would be affected (as they get their X chromosome from the mother) and daughters would be carriers for the trait. But here both sons and daughters are affected indicating that it is an X-linked dominant disorder. In the second generation we see that, in one family the father is affected, so both daughters are affected (daughters get one X-chromosome from the father), indicating that the trait is X-linked dominant. And when the mother is affected (in the second family) 50 percent children are affected and 50 percent unaffected irrespective of the sex. This again proves that it is X-linked dominant disorder.