X & Y Chromosomes

1. X & Y Chromosomes • Carry genes that determine whether a person is male or female • Female: two X chromosomes • Male: one X and one Y chromosome • Y chromosome is much smaller than X chromosome

2. Sex-linked Genes • Genes on the X and Y chromosomes are called sex-linked genes • These genes are passed on from parent to offspring on the X or Y chromosomes • Example: red-green colorblindness, muscular dystrophy, & hemophilia

3. Red-green Colorblindness Test #1 Red-green color blind should not be able to read any number

4. Red-green Colorblindness Test #2 Individuals with Red-Green color blindness should read the number 2

5. Females & Sex-linked Genes • Sex-linked genes can have dominant and recessive alleles • In females, a dominant allele on one X chromosome can hide recessive allele on the other X chromosome XCXc

6. Males & Sex-linked Genes • Males only have one X chromosome • No matching allele to hide recessive trait • Males are more likely to have a recessive sex-linked trait XcY

7. Carrier • Person who has ONE recessive allele for a trait and one dominant allele • Does not have the have the trait • Can pass on recessive alleles to offspring • In case of sex-linked traits, only FEMALES can be carriers XCXc

8. Sex-linked Punnett Squares