1. Sex-linked Traits
Using punnett squares

2. INHERITANCE OF SEX CHROMOSOMES
Humans have 23 pairs of chromosomes
Autosomes: 22 pairs are non-sex determining chromosomes
the 23rd pair determines the sex of the offspring

3. female sex chromosomes - XX

4. male sex chromosomes - XY
( y is smaller than x and has different genes)

5. Who determines the child's sex?
the male

6. SEX- LINKED TRAITS
an inherited trait that has a gene on the x chromosome but no
corresponding gene
on the y chromosome
(genes that only exist
only on the sex
chromosomes)

7. Examples of human sex-linked traits
Hemophilia
Red-green color blindness
Muscular dystrophy
Male pattern baldness

8. How to work sex-linked trait problems
Hemophilia: is a rare, inherited bleeding disorder in which your blood doesn’t clot normally. If you have hemophilia, you may bleed for a longer time than others after an injury. You also may bleed internally, especially in your knees, ankles, and elbows. This bleeding can damage your organs or tissues and, sometimes, be fatal.

9. All possible genotypes & phenotypes:
XHXH
XHXh
XhXh
XHY
XhY
Normal female
Female carrier
Female hemophiliac
Normal male
Male hemophiliac

10. What is a carrier?
carrier - expresses the normal characteristic but has both dominant and recessive genes (have the gene for a trait but do not express the trait themselves)
XHXh
for sex-linked traits, males cannot be carriers

11. How to work sex-linked trait problems: start with this type of punnett square
X X
X X Y
X Y
X Y

12. Cross a normal husband with a carrier wife
How to work sex-linked trait problems: put the genes on the X chromosome H h X X H H H H h X
X X
X X H h Y
X Y
X Y
Cross a normal husband with a carrier wife