1. SEX-LINKED INHERITANCE

2. What are Sex-Linked Traits?
Traits controlled by genes located on the sex chromosomes.
Most of these traits are X-linked – the Y chromosome is tiny, so there aren’t many genes on it.
The symbol for the allele is attached to an X or Y.

3. Males are more Affected by Recessive X-Linked Traits
This is because males only have one X chromosome
There’s no other allele to dominate over the recessive allele.
D is expressed
d is expressed

4. Examples Red-Green Colour Vision Deficiency Hemophelia
X-Linked Recessive
Hemophelia
Inability for blood to clot
Duchenne Muscular Distrophy
X-linked Recessive
Causes muscle degeneration
Fragile X Syndrome
X-linked Dominant
Can cause mental and social disorders
Rett Syndrome
Neurological Disorder

5. Example Problem 1: Red-green colour vision deficiency is an X-linked recessive disorder. A male with normal vision marries a heterozygous female. What is the chance the couple’s first child will be a male with normal vision?

6. Example Problem 2: Fragile X Syndrome is a dominant X-linked disorder
Example Problem 2: Fragile X Syndrome is a dominant X-linked disorder. If a heterozygous female has a child with an affected male, what is the chance of the child having Fragile X Syndrome?

7. Example Problem 3: Hemophilia is a recessive X-liked disorder
Example Problem 3: Hemophilia is a recessive X-liked disorder. A normal woman who’s father had hemophilia marries a normal man. What is the chance of the couple having a hemophiliac child?