Gender Effects on Phenotype

Certain autosomal traits are expressed differently in males and females, due to specific differences between the sexes.

A sex-limited trait affects a structure or function of the body that is present in only males or only females. Such a gene may be X-linked or autosomal. Beard growth and breast size are sex-limited traits. A woman cannot grow a beard because she does not manufacture sufficient hormones required for facial hair growth, but she can pass to her sons the genes that specify heavy beard growth. In animal breeding, milk yield and horn development are important sex-limited traits.

In sex-influenced inheritance, an allele is dominant in one sex but recessive in the other. Again, such a gene may be X-linked or autosomal. This difference in expression reflects hormonal differences between the sexes. For example, a gene for hair growth pattern has two alleles, one that produces hair all over the head and another that causes pattern baldness (fig. 24.13). The baldness allele is dominant in males but recessive in females, which is why more men than women are bald. A heterozygous male is bald, but a heterozygous female is not. A bald woman would have two mutant alleles.

About 1% of human genes exhibit genomic imprinting, in which the the expression of a disorder differs depending upon which parent transmits the disease-causing gene or chromosome. The phenotype may differ in degree of severity, in age of onset, or even in the nature of the symptoms. The physical basis of genomic imprinting is that methyl (CH3) groups are placed on the gene that is inherited from one parent, preventing it from being transcribed and translated.

Which chromosomes and genes determine sex?

What are the three classes of genes on the Y chromosome?

Why do sex-linked recessive conditions appear most commonly in males?

How can gender affect gene expression?

Hair Loss Prevention

Hair Loss Prevention

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