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प्रश्न
Give detail account of sex-linked inheritance.
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उत्तर
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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संबंधित प्रश्न
What is criss-cross inheritance?
Define the following:
Test cross
Answer the following question.
Explain linkage and recombination as put forth by T.H. Morgan based on his observations with the Drosophila melanogaster crossing experiment.
How many linkage groups do occur in human being?
______ results in separation of linkage groups during meiosis.
When a white eye Drosophila male (Xr Y) is crossed to a red eye female (XR XR), in the F2 generation all the females are red eyed and 50% males are white eyed. In a criss-cross test, when males are white eyed. In a criss-cross test, when a white eyed female (Xr Xr) is crossed to a red eye male (XRY), the F1 generation offspring had white eyed males while the female offspring bad red eyes. Instead of crossing of a white eyed female (Xr Xr} to a red eyed male (XRY), white eye female (XrXr) to white eye male (XrY) is crossed, the F1 generation will have the following phenotypes and genotype.
Analyse the following statements with respect to complete sex linkage and select the correct option.
- It is exhibited by genes located on non-homologous regions of X and Y chromosomes
- Y-linked trait is hypertrichosis.
- X-linked traits are haemophilia, red-green colour blindness, myopia (near sightedness).
Which of the following statement/s are INCORRECT with respect to crossing over?
i. Crossing over produces recombinations of genes by interchanging and exchanging corresponding segments between nonsister chromatids of homologous chromosomes.
ii. Crossing over occurs during zygotene of prophase I of meiosis.
From a cross AABb x aaBb, the genotypes AaBB : AaBb : Aabb will be obtained in the ratio ______.
When the parental gene combine with itself; termed as
