Question

Give detail account of sex-linked inheritance.

Answer 1

Definition: The inheritance of sex-linked genes from parents to their offsprings, is called sex-linked inheritance.

• X-linked (sex-linked) genes

1. The X-linked genes are located on the non-homologous region of the X chromosome and these genes do not have corresponding alleles on the Y chromosome.
2. As females have two X chromosomes two recessive X-linked genes are required for the expression of sex-linked traits.
3. If one X chromosome carries a recessive gene for the sex-linked trait (defect) its effect is suppressed by the dominant gene present on the other X chromosome.
4. The females with one recessive gene are carriers. The carrier female is physically normal as she does not suffer from the disease/disorder.
5. As males have only one X-chromosome if it carries an X-linked recessive gene for the sex-linked trait, then it is expressed phenotypically, because there is no dominant gene on the Y chromosome to suppress its effect.
6. Therefore, sex-linked / X-linked traits appear more frequently in males than in females.
7. Examples of X-linked traits include haemophilia, colour blindness, night blindness, myopia, muscular dystrophy, etc.

• Y linked genes

1. Genes located in the non-homologous region of the Y chromosome, are called Y linked genes or holandric genes.
2. The Y-linked genes are inherited directly from male to male.
3. In man, the Y linked genes such as hypertrichosis is responsible for excessive development of hair on the pinna of the ear. This character is transmitted directly from father to son.