1. 7.1 Chromosomes and Phenotype KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

2. 7.1 Chromosomes and Phenotype Autosomes are body chromosomes Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture.

3. 7.1 Chromosomes and Phenotype Autosomal gene expression –A heterozygote for a recessive disorder is a carrier. –Disorders caused by dominant alleles are uncommon. (dominant)

4. 7.1 Chromosomes and Phenotype Sex chromosomes are XX (girl) or XY (boy). Genes on sex chromosomes are called sex-linked genes. –Sex linked disorders are linked to the X chromosome Hemophilia, Colorblindness and ALD are all sex linked.

5. 7.1 Chromosomes and Phenotype Male mammals have an XY genotype. –All of a male’s sex- linked genes are expressed. –Males have no second copies of sex-linked genes –Example: X h Y.

6. 7.1 Chromosomes and Phenotype Female mammals have an XX genotype. –Expression of sex-linked genes is similar to autosomal genes in females. –Example : X H X H