SEX INFLUENCED TRAITS

DEFINITION:The traits that are dominant in males and recessive in females are called sex influenced traits.

These are autosomal traits. The sex influenced traits are exhibited in both the sexes. But these are dominant in males and recessive in females.

EXAMPLES

i. Baldness in human beings . Hair on head is character. The two contrasting forms are full hair and Bald hair. Baldness controlling gene 'B+' is dominant in male human being over full hair gene 'B-'. But in female human being, Bald ness gene 'B+' is recessive to full hair gene 'B-'. So one B+ gene is enough to cause baldness in males. Where as two baldness genes are required to cause baldness in female.

baldness

ii. Horns in sheep is a sex influenced trait. In males, horned gene 'H+' is dominant over hornless gene 'H-'. When horned Dorset variety was crossed with hornless sulflock, F, males contained horns and females were without horns. When F, horned male was crossed with hornless female, in F2 horned and horn males ratio is 3:1, where as horned and hornless females ratio is 1:3.

sheep-horn-genes

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