1. Sex Linked Traits
Males vs. Females

2. Sex Linked Traits Each person gets 2 chromosomes, 1 from each parent.
Humans have 23 pairs of chromosomes.
One pair of chromosomes is related to the sex of an individual , these chromosomes are called sex chromosomes

3. Karyotype Sex Linked Traits
The other 22 pairs of chromosomes are called autosomes (1-22)
Karyotype

4. Sex Linked Traits
In humans, the sex of an individual depends on the presence or absence of the Y chromosome
A normal human female is XX
A normal human male is XY

5. If the child receives an X from the father, it will be a girl
Every child receives an X from their mother, but they could get either an X or Y from dad.
If the child receives an X from the father, it will be a girl
If the child receives a Y from dad, it will be a boy.
Any couple has a 50% chance of having a daughter and a 50% chance of having a son. X Y XX XX XY XY

6. (c = colorblind, C = normal)
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

7. Sex Linked Traits
Sex linked traits are recessive, this means both x chromosomes must have the gene in order for the trait to be expressed.

8. Sex Linked Traits
If only one x chromosome is present (in males) and has the sex linked gene, then the trait will be expressed

9. (C= normal, c= colorblind)
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

10. Colorblindness

11. Sex Linked Punnett Squares
A colorblind male marries a normal female. What are the offspring genotypes and phenotypes? (C = normal, c = colorblind)
Xc Y XC
Genotype/Phenotype
2- female carriers
2- normal males
XC Xc
XC Y
XC Xc
XC Y

12. Sex Linked Punnett Squares
A normal male (not colorblind) marries a carrier. What are the offspring genotypes and phenotypes?
XC Y XC Xc
Genotype/Phenotype
1- female normal
1 - female carrier
1- normal male
1- Colorblind male
XC XC
XC Y
XC Xc
Xc Y

13. Sex Linked Punnett Squares
A normal male (not colorblind) marries a colorblind female. What are the offspring genotypes and phenotypes?
XC Y Xc
Genotype/Phenotype
2- female carriers
2- Colorblind males
XC Xc
Xc Y
XC Xc
Xc Y

14. Hemophilia Hemophilia is characterized by uncontrolled bleeding
It is a sex linked disorder caused by errors in the DNA that codes for the proteins involved in clotting

15. Hemophilia

16. Sex-Linked Traits Genotypes XAY XAXA N/A XAXa XaY XaXa Male Female
Homozygous Dominant
Carrier (Heterozygous)
Homozygous Recessive
XAY
XAXA
N/A
XAXa
XaY
XaXa

17. Sex-Linked Traits Phenotypes If sex-linked recessive
XA Y = normal male
Xa Y = affected male
XA XA = normal female
XA Xa = normal female, but carrier!
Xa Xa = affected female