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Question
Give detail account of sex-linked inheritance.
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Solution
Definition: The inheritance of sex-linked genes from parents to their offsprings, is called sex-linked inheritance.
- X-linked (sex-linked) genes
- 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.
- As females have two X chromosomes two recessive X-linked genes are required for the expression of sex-linked traits.
- 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.
- The females with one recessive gene are carriers. The carrier female is physically normal as she does not suffer from the disease/disorder.
- 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.
- Therefore, sex-linked / X-linked traits appear more frequently in males than in females.
- Examples of X-linked traits include haemophilia, colour blindness, night blindness, myopia, muscular dystrophy, etc.
- Y linked genes
- Genes located in the non-homologous region of the Y chromosome, are called Y linked genes or holandric genes.
- The Y-linked genes are inherited directly from male to male.
- 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.
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