Chapter 14 Sex-Linked Alleles Biology Chapter 14 Sex-Linked Alleles

Sex-linked Genes Special inheritance pattern for genes on X chromosome The Y chromosome is smaller than the X and only has a few genes

Sex-linked Genes Special inheritance pattern for genes on X chromosome The Y chromosome is smaller than the X and only has a few genes Females get two copies of each gene on the X chromosome Males get only one copy of each gene on the X chromosome In males, any defect in their single X chromosome is expressed.

Colorblindness (1 in 10 males, 1 in 100 females) Sex-linked Genes Special inheritance pattern for genes on X chromosome The Y chromosome is smaller than the X and only has a few genes Females get two copies of each gene on the X chromosome Males get only one copy of each gene on the X chromosome In males, any defect in their single X chromosome is expressed. Colorblindness (1 in 10 males, 1 in 100 females) •Controlled by three genes on X chromosome •In males, a defect in any one of them produces red-green colorblindness •Women are much less likely to have red-green colorblindness because they have two copies of each gene, two chances to get it right. Males have only one X chromosome, so all X-linked alleles are expressed in males

Colorblindness (1 in 10 males, 1 in 100 females) •Controlled by three genes on X chromosome •In males, a defect in any one of them produces red-green colorblindness •Women are much less likely to have red-green colorblindness because they have two copies of each gene, two chances to get it right. Males have only one X chromosome, so all X-linked alleles are expressed in males

Hemophilia (1 in 10,000 males, Extremely rare in females) •Two genes that control blood clotting are carried on 2 genes of X-chromosome •A recessive allele at either gene may cause hemophilia •Resulting in a missing blood-clotting protein

Duchenne Muscular Dystrophy •Progressive weakening of skeletal muscles Hemophilia (1 in 10,000 males, Extremely rare in females) •Two genes that control blood clotting are carried on 2 genes of X-chromosome •A recessive allele at either gene may cause hemophilia •Resulting in a missing blood-clotting protein Duchenne Muscular Dystrophy (1 in 3,000 males, Extremely rare in females) •Progressive weakening of skeletal muscles •Early death (rarely live past thirties)

X-linked Allele Puzzler 2. A man who suffers from hemophilia and a woman who does not suffer from the condition have a daughter who is a hemophiliac. They are about to have a second child, a son. What is the probability that their son will also be a hemophiliac? Explain your answer and draw a Punnett square to show your reasoning. If we already know this next child is a boy, it has a 50/50 chance of having hemophilia. Father phenotype: hemophilia Genotype: XhY Y Xh Mother phenotype: Non-hemophilia Genotype: XHX? XHXh XHY XH XhY Because this daughter is hemophiliac, mother must carry The allele Xh. Xh X? XhXh

X-linked Allele Puzzler Hemophilia is a recessive allele on the X-chromosome, usually written Xh. Draw a Punnet square to show the cross between a woman who suffers from hemophilia and a man who does not. Refer to your Punnett square to answer these questions: If they have a boy, what are the chances he will be a hemophiliac? If they have a girl, what is the probability she will be a hemophiliac?

X-linked Allele Puzzler Hemophilia is a recessive allele on the X-chromosome, usually written Xh. Draw a Punnet square to show the cross between a woman who suffers from hemophilia and a man who does not. Refer to your Punnett square to answer these questions: If they have a boy, what are the chances he will be a hemophiliac? If they have a girl, what is the probability she will be a hemophiliac? Father phenotype: nonhemophilia Genotype: XHY Y XH Mother phenotype: Hemophilia Genotype: XhXh All of the boys will be hemophiliacs None of the girls will be hemophiliacs XHXh XhY Xh XhY Xh XHXh