1. Non-Mendelian: Sex- Linked Traits
Determining Sex (Gender)
Humans have a diploid number of 46 chromosomes or 23 pairs
22 of the pairs are autosomes, they are the same for males and females
The 23rd pair of chromosomes differ in males and females
These are the sex chromosomes and are indicated by X and Y
XY = male
XX = female

2. The Male determines the baby’s sex because only men give the Y chromosome

3. Sex- Linked Traits Inheriting sex-linked traits
Genes located on the sex chromosomes are called sex-linked traits
Because the Y chromosome is small it carries few genes, along with the male determinant sex gene.

4. Sex- Linked Traits Inheriting sex linked traits
Males who receive a recessive allele on the X chromosomes will express the recessive phenotype because he cannot inherit an allele on the Y chromosome.
There is no dominant allele to overpower the recessive gene so it is expressed.
Males have a higher percent chance of expressing the recessive trait

5. Sex- Linked Traits Examples in Humans Hemophilia
Causes a problem with blood clotting
Caused by a recessive allele 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 carrier mom and one from affected dad

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

7. Sex- Linked Traits Examples in Humans 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

8. 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?

9. Sample problem Xc’Y XCXC
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
Key:
Parents:
c. Genotype:
d. Phenotype:
XX= female XY= male
C= normal c’= colorblind
Xc’Y XCXC
2 XCY XCXc’
2 female carriers
2 normal males

10. Do all 5 steps!
A colorblind woman has children with a normal sighted man. What are the chances their children will have normal sight?