Sex Limited Traits
The traits limited to only one sex due to anatomical differences are called sex limited traits. Such trait affects a structure or function of the body of males or females only. These traits are controlled by sex-linked or autosomal genes.
For example:
(i) Genes for milk production in dairy cattle affect only cows.
(ii) Beard growth in humans is limited to men. A woman does not grow a beard herself. But she can pass the genes of heavy board growth to her sons.
Sex hormones and other physiologic differences between males and females effect on expression of certain gene. For example, premature baldness is an autosomal dominant trait. But this condition is rarely expressed in the female due to female sex hormones. It appears in them only after menopause.
Sex Influenced Traits
The autosomal traits occur in both males and females but are more common in one sex are called sex influenced trait. Their allele is expressed as dominant in one sex but recessive in the other. Both male and females secretes different hormones. These hormones affect the expression of trait. Pattern baldness is a sex influenced trait. More men are bald than the women. It is an autosomal dominant trait in males. But it is an autosomal recessive trait in females. A heterozygous male is bald. But a heterozygous female is not bald. Only a homozygous recessive woman is bald.
Holandric genes:
Holandric genes are genes situated in the non-homologous region of the Y chromosome. Holandric genes condition phenotypes that emerge only in men since individuals of the female sex do not present in their X chromosomes genes from the non-homologous portion of the Y chromosome existent only in men.
Holandric qualities are traits that are only passed down from father to son. These are Y-linked features. TDF (testis-determining factor) is the example of holandric gene. These are known as holandric characteristics. Only men have holandric genes, which are only found on the Y chromosome.
Download PDF file here
Comments
Post a Comment