1. Complex patterns of inheritance
Section 12.2

2. Incomplete dominance
Phenotype of heterozygous individuals is intermediate between those of the 2 homozygotes.

3. Incomplete Dominance example
CRCR
CRCW
CWCW

4. Codominance
Phenotypes of both homozygotes produced in heterozygous individuals. (both alleles expressed equally).

5. Codominance Example RR RW WW

6. Multiple Alleles
An inheritance pattern in which traits are controlled by more than 2 alleles

7. Multiple Alleles example
IA IA IA Ii
IAIA
IAIi

8. Sex Determination
Humans have 23 pairs of chromosomes

9. Sex Determination
Of the 23 pairs of chromosomes in humans, 22 are autosomes (pairs that look alike) and 1 are sex chromosomes.

10. Sex Determination
A karyotype is a diagram of the chromosomes (arranged in order for study)

11. Sex Determination Sex chromosomes are indicated by the letters X and Y
Females sex chromosomes are XX
Male sex chromosomes are XY
Who controls the sex of offspring?
Males (Sperm)
Why?
All female eggs carry X chromosome. Sperm carry X or Y

12. Sex-linked inheritance
Sex-linked traits: characteristics determined by genes on sex chromosomes
Can sex-linked traits be on the X or Y chromosome?
Yes
Which is more common?
X chromosome

13. Sex-linked inheritance
Alleles are written as superscripts for X and Y for sex linked traits
What does it look like?
XRXr or XrY

14. Color Blindness C = normal c = color blind
Male with color blindness = XcY
Female with color blindness = XcXc

15. Color Blindness Female carrier of color blindness = XCXc
Normal (non-carrier) = XCXC
Why can only females be carriers of X-linked traits?
Males only have one X-chromosome. If the trait is on the X chromosome they will be colorblind.
Can males or females pass on y-linked traits?
Only males

17. Practice
Hemophilia is a lethal recessive sex linked trait. It causes your blood to be unable to clot. So, if you fall and cut your chin open, the blood will keep spurting out of your chin! If Queen Victoria carries a recessive trait for hemophilia XHXh and marries Albert who has hemophilia XhY. How many of their children will die from hemophilia?

18. Polygenic traits
Traits caused by more than one gene