2. Genes that are located on the sex chromosomes are sex-linked genes. In mammals, individuals with two X chromosomes, an XX genotype, are females. Individuals with one X and one Y, an XY genotype, are males. The father’s gametes determines the sex of an organism. Some genetic disorders are sex-linked such as Duchenne Muscular Dystrophy, Hemophilia, and color blindness

3. Occurs when a heterozygous phenotype is somewhere between the two homozygous phenotypes. Neither allele is completely dominant or recessive. Ex: When plants that are homozygous for red flowers are crossed with plants that are homozygous for white flowers, the offspring have pink flowers.

4. Occurs when both alleles of a gene are expressed completely, neither allele is dominant or recessive (so both traits are fully expressed). Ex: A plant that is homozygous for red flowers is crossed with a plant that is homozygous for white flowers. The offspring will have some red areas and some white areas.

5. Polygenic traits are traits produced by two or more genes. Ex: Human skin color is a result of four genes that interact to produce a continuous range of colors. Ex: Three genes determine eye color.