2. Sex influenced traits The gene is NOT on a sex chromosome, but SEX affects the phenotype Ex-baldness-dominant in males, recessive in women –If ‘B’ represents bald and ‘b’ is hairy then Men must be bb to keep hair Women can be Bb or bb to keep hair

3. Caused by a gene that is located on a SEX chromosome (X or Y) Most SEX-linked Traits are found on the X chromosome

4. X-linked diseases Most are recessive Examples-hemophilia, red-green colorblindness Males are more likely to have these because they cannot be carriers Why? Males are XY-if their ‘X’ has a bad gene, there is nothing on the ‘Y’ to dominate over it

5. How A Sex-linked trait is passed Ex. Red-Green Colorblindness (x-recessive) N n X N X N =Normal X N X n =CARRIER, but IS NOT colorblind X N Y=Normal X n Y=HAS red-green colorblindess

6. Passing colorblindness Carrier mom X N X n Normal Dad X N Y X N X n X N X N X N X N X n Y X N Y X n Y

7. X-linked genes are on the X chromosome

8. Autosomal genes-NOT on the X or Y chromosomes

9. Other X-linked traits Orange and Black Alleles are on the X chromosome in cats White is on another chromosome In every cell, only 1 X chromosome is active (other X is Barr Body) Result-some cells make black fur, some orange

10. Multifactorial and polygenic traits Polygenic-more than one pair of alleles determines phenotype- -eye color Multifactorial-genes AND environment determine phenotype –weight and height

11. Epistasis Multiple alleles (more than 2 involved) One allele causes the other to act differently) Example-E is brown unless B is present