Answer: Option B
:
B
From the chart we can see that the male parent is affected while the female parent is unaffected. In the first generation, out of four children, both daughters are affected . X-linked dominant disorders are caused by mutations in genes on the X chromosome, one of the two sex chromosomes in each cell. In females (who have two X chromosomes), a mutation in one of the two copies of the gene is sufficient to cause the disorder. In males (who have only one X chromosome), a mutation in the only copy of the gene causes the disorder. The daughters by default, inherit one X-chromosome from the mother and one X-chromosome from the father. Moreover,in the chart, we can see that father is affected, which means he has the defective allele on the X-chromosome which he has passed on to his daughters. In the second generation again we see that, both affected mothers, pass on the disease to all their children, daughters and sons both. This is possible only when the X-linked defective allele is dominant. If the X-linked defective allele was recessive, daughters wouldnot have been affected in this scenario.