Question

Write a note on sex-linked inheritance.

Answer 1

Sex linkage is the phenotypic expression of an allelerelated to the allosome (sex chromosome) of the individual. In autosomal chromosomes both sexes have the same probability of existing (see Fisher's principle), but since humans have many more geneson the female X chromosome than on the male Y chromosome, these are much more common than Y-linked traits.

In mammals, the female is homogametic, with two X chromosomes (XX), while the male is the heterogametic sex, with one X and one Y chromosome (XY). Genes on the X or Y chromosome are called sex-linked. In ZW sex-determination system used by birds the opposite is true: the male is the homogametic sex (ZZ), and the female is heterogametic (ZW).

X-linked recessive traits are expressed in all heterogametics, but are only expressed in those homogametics that are homozygous for the recessive allele. For example, an X-linked recessive allele in humans causes haemophilia, which is much more common in males than females because males are hemizygous (see zygosity) and therefore express the trait when they inherit one mutant allele. In contrast, a female must inherit two mutant alleles, a less frequent event since the mutant allele is rare in the population.

Answer 2

Dear Student,

◆ Sex-linked inheritance -

• Transfer of traits from parents to children through sex chromosomes.
• Gene responsible is recessive and present on X-chromosome.
• Usually males are affected by the disease but females are only carriers.
• Diseases having sex-liked inheritance are color blindness, hemophilia, Duchene muscular dystrophy and Becker muscular dystrophy.

Thanks dear. Hope this helps you...