1. Notes: Sex-Linked Traits
Essential Question: What are sex-linked traits and how do they work?

2. What is a karyotype? Picture that shows all the chromosomes.
Humans have 23 pairs of chromosomes. (46 total)
One pair of chromosomes are called sex chromosomes
normal female = XX
normal male = XY

3. What is a karyotype?
The other 22 pairs of chromosomes are called autosomes

4. How is gender determined?
According to this:
What percentage chance is there getting a son?
% chance getting a daughter?
Who determines the sex of the offspring?

5. What are sex-linked traits?
Genes that are located on the X chromosome are called sex-linked genes.
Traits determined by sex-linked genes are called sex-linked traits
 (c = colorblind, C = normal)
Ex. Color blindness
female: Xc Xc
male: Xc Y

6. (C= normal, c= colorblind)
What are carriers?
A carrier is a person that has the trait on only one chromosome and does not express the trait.
Carriers of sex linked traits are always women.
(C= normal, c= colorblind)
Ex. Color blind carrier XC Xc

7. Practice 1: Determine the phenotype
Given hemophilia is a sex linked gene: (H = normal, h = hemophiliac)
Write down the phenotype and sex for the following:
- XH XH
- XH Y
- XH Xh
- Xh Y
Female, normal
Male, normal
Female, normal, carrier
Male, hemophiliac

8. Practice 2: Determine the genotype
Given that color blindness is a sex linked gene: (C = normal, c = colorblind)
Write down the genotypes for the following:
- Male normal sight
- Male color blind
- Female normal sight
- Female color blind
XC Y
Xc Y
XCXC or XCXc
Xc Xc

9. Practice 3: Punnett square problem
Colorblind-ness is a sex-linked trait. A colorblind male marries a normal female (not a carrier). What are the offspring genotypes and phenotypes? (C = normal, c = colorblind)
1st Step: figure out the parents genotypes:
Male =
Female =
Xc Y
XC XC

10. Practice 3: Punnett square problem
Colorblind-ness is a sex-linked trait. A colorblind male marries a normal female (not a carrier). What are the offspring genotypes and phenotypes? (C = normal, c = colorblind)
1st Step: Figure out the parents Genotype
Dad genotype = ______
Mom genotype = ______
XcY
XCXC

11. Practice 3: Punnett square problem
Colorblind-ness is a sex-linked trait. A colorblind male marries a normal female (not a carrier). What are the offspring genotypes and phenotypes? (C = normal, c = colorblind)
XCXC XC XC
Dad genotype = ______
Mom genotype = ______
XcY
XCXc
XCXc Xc
XCXC
XcY Y
XCY
XCY

12. Practice 3: Punnett square problem
Colorblind-ness is a sex-linked trait. A colorblind male marries a normal female (not a carrier). What are the offspring genotypes and phenotypes? (C = normal, c = colorblind)
3rd Step: Analyze the Punnett Square: 1) 2) 3) 4) XC Xc Y
XCXc
XCY
Female, normal
Female, normal 1 2
Male, normal
Male, normal 3 4

13. Extra Practice Problem
In fruit flies eye color is a sex-linked trait. Red eyes (R) are dominant over white eyes (r). Show the cross between a white-eyed female fruit fly and red-eyed male.
XrXr Xr Xr
Dad genotype = ______
Mom genotype = ______
XRY
XRXr
XRXr XR
XrXr
XRY Y
XrY
XrY