1. Sex-Influenced Genes

2. Sex-Influenced Genes
Certain traits, although not located on the sex chromosomes, have different appearances in males and females.
E.g. Pattern Baldness

3. Pattern Baldness This is inherited and controlled by a single gene.
In females the gene acts as a recessive, so a woman must have two recessive genes to show baldness.
In men, only one baldness gene is needed.

4. Pattern Baldness BB – full hair in both sexes
Bb – baldness in men, not in women
bb – baldness in both sexes
Women tend to lose hair evenly all over the head resulting in very thin hair. This is more pronounced after menopause.

5. Sex-Influenced Genes
These genes are influenced by the presence of sex hormones.
E.g. a bull may carry genes for high milk production, but he will not give milk. He would be a good sire for a dairy herd.
Secondary sexual characteristics depend on the presence of the sex hormones for their expression. These in turn depend on the presence of X and Y chromosomes.

6. Sex-Influenced Genes
E.g. a single pair of alleles determines the presence or absence of horns on sheep. H = horns is dominant in males but recessive in females; h = hornless is recessive in males but dominant in females.
HH- horns in both sexes
Hh- horns in males
hh- no horns in both sexes.