1. Sex-linked Traits
Ch. 10.5

2. Sex chromosomes Humans- 23rd pair of chromosomes- X,Y
Eggs- Have an X chromosome.
Sperm- Half have an X chromosome, half have a Y chromosome.
Fathers determine gender(sex) of offspring.
Males- XY
Females- XX
50% chance of having a girl or boy offpring.

3. Sex-linked genes Any gene on a sex chromosome- X or Y.
Majority are on X chromosome.
Examples-
Eye color in fruit flies- on the X chromosome
Red color is Normal and Dominant, XR
White color is Recessive. Xr
Females must have 2 recessive alleles to have white eyes. Xr Xr
Males need just 1 recessive allele ( they have only 1 X chromosome) Xr Y to have white eyes.

4. Eye Color in
Fruit flies

5. Human X-linked recessive traits.
Hemophilia- bleeding disorder
Red-green color blindness.
more males with the disorder compared to females.
Females can be carriers- have one recessive allele- do not have the disorder, but can pass on the recessive allele to offspring.
Mothers pass trait on to sons.
Pedigree- Chart used to record and trace the occurrence of a trait in a family.
Squares- males
Circles- females.
Colored shapes- individuals that show the trait.
Parents are connected by horizontal lines(marriage line)
Children beneath them.
Generations – designated by Roman Numerals ( I, II, III etc)
Individuals are Numbered left to right in each generation.

6. Sex-linked recessive pedigree skips generations , see more often in males.