1. Sex-Linked Traits
Most traits are controlled by at least 2 genes, one on each homologue
The exception are traits controlled by genes on the sex chromosomes
Some genes on the X are not on the Y
In males, the trait is only controlled by 1 gene
Males are not homozygous or heterozygous, by are called hemizygous (only 1 chromosome has the gene)

2. Sex-Linked Traits
Males either have a dominant or recessive allele; no heterozygous genotypes
Males generally show the recessive traits more (50% to 33%)
Male: H or h Female: HH, Hh, hh
Types of disorders found on the X chromosome:
Hemophilia – blood doesn’t clot
Color-blindness – can’t see certain colors (red - green)
Duchene Muscular Dystrophy – affects cardiac/skeletal muscle; those with this disorder usually die in early 20s

3. Colorblindness Test

4. Sex-Linked Traits Y Xh XH Xh
Females that are heterozygous for X-linked disorders are called Carriers: they don’t show the disorder but carry the defective gene
Method to complete sex-linked Punnett squares is the same as before, except you use X and Y for the genotypes
Ex: Cross a hemophilic male with a carrier female
Genotypes:
Phenotypes: Xh Y XH Xh

5. Sex-linked Punnett Genotypes: Phenotypes
Cross a male with colorblindness with a normal female
Genotypes:
Phenotypes