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 Review-Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture. BUT Patterns of inheritance are often complex!

3. 7.1 Chromosomes and Phenotype Mendel’s rules of inheritance apply to autosomal genetic disorders. –A heterozygote for a recessive disorder is a carrier. –Disorders caused by dominant alleles are uncommon. (dominant)

4. 7.1 Chromosomes and Phenotype Males and females can differ in sex-linked traits. Genes on sex chromosomes are called sex-linked genes. –Y chromosome genes in mammals are responsible for male characteristics. –X chromosome genes in mammals affect many traits.

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.

6. 7.1 Chromosomes and Phenotype (1).X-linked traits or sex-linked traits. Studied by American Scientist-Thomas Hunt Morgan studied eye color of Drosophila melanogasta –fruit fly. A pattern of inheritance when traits are controlled on the sex chromosome, not on the autosomes (#1-22). If a male inherits the recessive trait on the x chromosome, the recessive trait will always be expressed. The Y chromosome has no corresponding allele for an x- linked trait. ( It is not there!) Two examples in humans are : Hemophilia and color blindness

7. 7.1 Chromosomes and Phenotype

9. Female mammals have an XX genotype. (2)X chromosome inactivation randomly “turns off” one X chromosome which results in two types of cells- females can be black, orange, and white. X-white (both males and females), X0, orange, Xo- black