1. sex-linked traits

2. Sex chromosomes carry genes that code for traits other than gender. Traits determined by genes on the X chromosome are called sex-linked traits. (hemophilia and colour blindness) A male has XY homologous chromosomes for sex determination. A female has XX homologous chromosomes for sex determination.

3. Receives sex-linked chromosome from mother (give the X) Phenotype will show sex-linked gene because no other allele to mask it. x y

4. Can inherit sex-linked traits from either parent. Must have two sex-linked alleles to show recessive trait. If receives one recessive sex-linked allele, she will not show the trait, but she is a carrier. x x

5. Father = XY Mother = XX X Y X X X X X X Y Y X X ½ disorder free – 50% ¼ color-blind male – 25% ¼ female carrier – 25%

6. A pedigree is a diagram representing the phenotype history of a family. Genotypes can be determined by analyzing the pedigree. Symbols: Male – square Female – circle Dominant trait – blank Recessive trait – filled

7. A widow's peak hairline (W) is dominant over a straight hairline (w): ww W WW W W W W w w ww w ? ?