1. Sex-Linked Traits

2. Sex Chromosomes X Chromosome Y Chromosome XX = Female XY = Male Larger
Can hold more genes
Y Chromosome
Smaller
Holds less genes
XX = Female
XY = Male

3. Location
Sex-linked traits are located on either the X or the Y chromosomes and therefore get passed down with those chromosomes
If a male has a child he can either pass down an X or a Y chromosome
If a female has a child she can only pass down one of her two X chromosomes

4. Examples
If the gene for colorblindness is located on the Y chromosome of a male and he has a son, he will pass the trait for colorblindness down to his son.

5. How to Write Sex-Linked Traits on the X Chromosome:
Female Dominant: XNXN
Female Heterozygous: XCXn
Female Recessive: XnXn
Male Dominant: XNY
Male Recessive:XnY

6. How to Write Sex-Linked Traits on the Y Chromosome:
Male Dominant: XYN
Male Recessive: XYn

7. Dad’s Genotype:_____ Mom’s Genotype:_____
Hemophilia is a recessive sex linked genetic disorder where people infected do not clot normally. The trait for hemophilia is carried on the X chromosome. Mom does not carry the gene for hemophilia and Dad has hemophilia. What are the parents genotypes?
Dad’s Genotype:_____
Mom’s Genotype:_____
Use a Punnett square to determine what percentage of the offspring would have hemophilia.

8. Dad XhY Xh Y XH XH Xh XH Y XH Xh XH Y XH
Mom XHXH

9. Mom’s Genotype:______
Mom has hemophilia and Dad does not have hemophilia. What are the parents genotypes?
Mom’s Genotype:______
Dad’s Genotype:______
Use a Punnett square to determine what percentage of the offspring would have hemophilia.

10. Dad XHY XH Y Xh XH Xh Xh Y XH Xh Xh Y Xh
Mom XhXh

11. Mom’s Genotype:______
Mom is heterozygous (carrier) for hemophilia and Dad has hemophilia. What are the parents genotypes?
Mom’s Genotype:______
Dad’s Genotype:______
Use a Punnett square to determine what percentage of the offspring would have hemophilia.

12. Dad XhY Xh Y XH XH Xh XH Y Xh Xh Xh Y Xh
Mom XHXh