Ans. B: X-linked recessiveAn male affected with X-linked recessive disorder does not transmit the disorder to his son, hut all daughters are carriersX-linked recessive inheritanceIt is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed- In males (who are necessarily hemizygous for the gene mutation because they have only one X chromosome) and- In females who are homozygous for the gene mutation (i.e., they have a copy of the gene mutation on each of thee' two X chromosomes).X-linkec inheritance means that the gene causing the trait or the disorder is located on the X chromosome.Females have two X chromosomes, while males have one X and one Y chromosome.Carrier females who have only one copy of the mutation do not usually express the phenotypeGenerally "men are affected and women are carriers" for two reasons.The first is the simple statistical fact that if the X-chromosomes is a population that carry a paicular X-linked mutation at a frequency of 'f' (for example, 1%) then that will be the frequency that men are likely to express the mutation (since they have only one X), while women will express it at a frequency of f2 (for example 1% *1% = 0.01%) since they have two X's and hence two chances to get the normal allele.Thus, X-linked mutations tend to be rare in women.Father can pass only Y-chromosome to his son, which is never involved in X-linked recessive conditions, as the gene, is located on the X-chromosome. Hence disease will not pass from father to son.Most common X-linked recessive disordersColor blindness; a classic example of an X-linked trait because it is relatively common.- 7% to 10% of men are red-green colorblindIts commonness may be attributable to its not being a serious disability in most cases and an actual advantage in some situations (for example, not being distracted by some of the color in color based camouflage).It is also known as daltonism.Hemophilia ADuchenne muscular dystrophy; muscular dystrophy associated with mutations in the dystrophin gene, characterized by rapid progression of muscle degeneration, eventually leading to loss in ambulation, respiratory failure and death.Becker's muscular dystrophy; milder form of Duchenne, causes slowly progressive muscle weakness of the legs and pelvis.Hemophilia B; disorder caused by a mutation of the Factor IX gene, leading to a deficiency of Factor IX. It is rarer than haemophilia A. It's also called Christmas diseaseX-linked ichthyosis; ichthyosis caused by the hereditary deficiency of the steroid sulfatase (STS) enzyme that affects 1 in 2000 to 1 in 6000 males.X-linked agammaglobulinemia (XLA); XLA patients do not generate mature B cells. B cells are pa of the immune system and normally manufacture antibodies (Immunoglobulins) which defends the body from infections (the humoral response).Glucose-6-phosphate dehydrogenase deficiency; may exhibit nonimmune hemolytic anemia in response to a number of causes, most commonly infection or exposure to ceain medications or chemicals.