Thursday, November 29, 2012

Sex-linked inheritance

Sex-linked inheritance 

There are two types of chromosomes in living organisms i.e autosomes and sex chromosomes.autosomes bear genes for somatic organ nd sex chromosome to deermine sex of a individual.most female have two rod shaped xx chromosomes and male have a rodshaped and other hooked shaped xy chromosomes.
genes located in x-chromosomes are sex linked genes and pattern of inheritance of such gene is called sex-linked inheritance.
sex genes usually are inherited along with x-chromosomes . usually y chromosomes are genetically inert.genes of y-chromosomes are called holandric genes.

CHARACTERISTICS 
1. The y-chromosome donot carryany homologous region of x-chromosomes.male have only one x-chromosome and so a trait expresses even if it is present in recessive form.
2.A female have two x-chromosome and so has to become homozygous to express a recessive trait.that means she must receive mutant allele from both parents.
3.A female receives one x-chromosome from her father which she subsequently transmit to her children,meaning that her children would get the grandfather's sex-linked trait.
4.A male transmits his sex-linked traits to his grand children via his daughter.this is called criss-cross inheritance.
5.A father cannot transmit sex-linked traits to his son because x-chromosome of son is always from the mother.
6. From a female,sex-linked gene goes both to son and daughters.
7.In all sex-linked traits,heterozygous females are the carriers .they are phenotypically normal but carry the trait in the genes.
8. The recessive x-linked disease are seen more in male than in female.

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