Non-Mendelian: Sex- Linked TraitsA.Determining Sex

1.Humans have a diploid number of 46 chromosomes or 23 pairs

2.22 of the pairs are autosomes, they are the samefor males and females

3.The 23rd pair of chromosomes differ in males and females

The are the sex chromosomes and are indicated by X and Y

XY = male XX = female

• Males determine the baby’s sex because only men give the Y chromosome

IX.Sex- Linked Traits

B.Inheriting sex linked traits1.Genes located on the sex chromosomes

are called sex- linked traits2.Because the Y chromosome is small it carries

few genes, including the male determinant sex gene.

IX.Sex- Linked TraitsB.Inheriting sex linked traits

3.Males who receive a recessive allele on the X chromosomes will express the recessive phenotype because he cannot inherit on the Y chromosome. o There is no dominant

allele to overpower the recessive gene

4.Males have a higher percent chance of expressing the recessive trait

C.Examples in Humans

1. Hemophilia

Causes a problem with blood clotting

Caused by a recessiveallele on the X chromosomes

Males: 1/10,000

Need one recessive allele from carrier mom

Females: 1/10,000,000

Need two recessive alleles; one from mom and one from dad

IX.Sex- Linked Traits

A woman who is heterozygous (a carrier) for hemophilia marries a normal man:

Queen Victoria of England was a carrier of the gene for hemophilia. She passed the harmful allele to 4 sons and 2 daughters. Her son Leopold had the disease and died at age 30, while her daughters were only carriers. As a result of marrying into other European royal families, the princesses Alice and Beatrice spread hemophilia to Russia, Germany, and Spain. By the early 20th century, ten of Victoria's descendents had hemophilia. All of them were men, as expected.

C.Examples in Humans

1.Red-Green Color Blindness

People who have red-green color blindness cannot differentiate between the two colors.

Caused by a recessive allele on the X chromosomes

IX.Sex- Linked Traits

Are you colorblind?

Colorblindness

The allele that controls colorblindness is found on the X chromosome and is recessive .

What genotype must a female have to be diagnosed as colorblind?

Sample problem

A colorblind man marries a woman who is not colorblind.

Assuming there is no colorblindness in the woman’s ancestry,

what will most likely be the genotype and phenotypes of their

sons and daughters? Show your work

a. Key:

a. Parents:

c. Genotype Ratio:

d. Phenotype Ratio:

XX= female XY= maleC= normal c’= colorblind

Xc’Y XCXC

1:2 female carriers 1:2 normal males

1:2 XCY 1:2 XCXc’

Feb 5th Do all 5 steps!

1.Cross a heterozygous B blood type with an AB blood type.

2.A colorblind woman has children with a normal sighted man. What are the chances their children will have normal sight?