Mendel studied autosomal gene traits The “either-or” traits that were seen in your tutorial. Genes found on autosomes (1-22 for humans) = autosomal traits Genes found on sex chromosomes (pair 23 for humans) = sex-linked traits KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

Males and females can differ in sex- linked traits. – Y chromosome genes in mammals are responsible for male characteristics. – X chromosome genes in mammals affect many traits.

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. –Because of this, males can never be “carriers” of sex- linked traits or disorders. –Ex: Colorblindness, Hemophilia, Muscular dystrophy

4 Sex-Linked Traits: 1. Normal Color Vision: A: 29, B: 45, C: --, D: Red-Green Color-Blind: A: 70, B: --, C: 5, D: Red Color-blind: A: 70, B: --, C: 5, D: 6 4. Green Color-Blind: A: 70, B: --, C: 5, D: 2 Sample Colorblind Tests

Let’s take a look at…

Lynda is a healthy carrier of colorblindess and her husband, Jim, has no family history of colorblindness. Lynda’s genotype: XX d Jim’s genotype: XY What is the probability of getting: A colorblind daughter? 0% Carrier child? 25% A colorblind child? 25% Two healthy children? ¾ x ¾ = 9/16 (56%)

Jen is a healthy carrier of hemophilia and Adam has no history in his family. What is the probability of getting: Daughter with hemophilia? 0% Carrier child? 25% Child with hemophilia? 25% Two healthy children? ¾ x ¾ = 9/16 (56%)

Kelly is a healthy carrier of hemophilia, but Joe suffers from the disease. What is the probability of getting a: Healthy son? 25% Healthy daughter? 25% Child with hemophilia? 50% Carrier child? 25%

We use PEDIGREES to trace: Autosomal traits Sex-linked traits Autosomal disorders or diseases Sex-linked disorders or diseases

If the phenotype is more common in males, the gene is likely sex-linked.

Let’s try a sex-linked problem: A man and a woman marry. The woman is a carrier of colorblindness, an X-linked disorder. They have 4 children, 3 boys and one girl. Two of the boys are colorblind, and the girl is a carrier. The carrier daughter marries a healthy man. a)What is the probability they will have carrier daughters? b)What is the probability they will have sons that are colorblind? ? a) ½ daughter x ½ carrier = 25% b) ½ son x ½ c.b. = 25%

Fill in the X-linked Pedigree