1. Patterns of Inheritance

2. Dominance
One copy of a gene is enough for a trait to show. In heterozygotes, the dominant trait shows, not the recessive.
2 Phenotypes:
Dominant (H) and recessive (h)
Examples:
Huntington’s Disease
Achondroplasia (dwarfism)
Tongue Rolling

3. Dominance h h H H h H h h h h h h
A man who is heterozygous for Huntington’s Disease marries a normal woman. What is the chance that their offspring will have the disease? h h H H h H h h h h h h

4. Recessiveness
Trait only shows if there are no dominant alleles. Heterozygotes have the dominant phenotype.
2 Phenotypes:
Dominant (H) and recessive (h)
Examples:
Albinism
Cystic Fibrosis
Hitchhiker’s Thumb

5. Recessiveness f f F F f F f F F f F f
A woman with cystic fibrosis wants to minimize her chances of passing the disease to her children. Which genotype of man would be best for producing children without the disease? f f F F f F f
She should marry a man
Who is homozygous, FF
For the normal allele. He
Would not be a carrier,
But all their kids would be. F F f F f

6. Codominance
Two alleles are both dominant. When they occur together, both phenotypes show up completely, without blending.
3 Phenotypes
CC, CS, SS
Examples:
Sickle Cell
Roan cattle
Erminette chickens

7. Codominance
A black chicken is crossed with an erminette chicken. What ratio of feather colors would be expected in the offspring? B W B B B B W B B B B W

8. Incomplete Dominance
Neither of two alleles are completely dominant. In a heterozygote, both traits show up, but their effects are blended.
3 Phenotypes
RR, RW, WW
Examples:
Hair curliness
Snapdragons

9. Incomplete Dominance
A curly haired woman and a straight haired man have a baby. What must be the hair texture of their child? C C S C S C S
All babies will have
wavy hair, CS (half-
way between curly
snd straight. S C S C S

10. Sex-linked
Gene controlling the trait is located on the X chromosome (also called X-linked). Males are affected more often than females
4 Phenotypes
XHXH, XhXh, XHY, XhY
Examples:
Red-green Colorblindness
Hemophilia
Male-pattern baldness

11. Sex-linked
A man with hemophilia marries a woman who is a carrier for the disease, what percent of their sons will have hemophilia?
Xh Y XH XH
Xh Y XH
50% of the males
(shaded green) would
have hemophilia. Xh Xh
Xh Y Xh

12. Multiple Alleles
More than two alleles control a single trait. There may be any combination of dominant or recessive alleles.
The number of phenotypes can vary, but is usually greater than 3.
Examples:
Blood type
Alleles IA, IB, and i

13. Multiple Alleles
A woman with AB blood (IAIB) gave birth to a baby with AB blood. Could a type O man (ii) be the baby’s father?
i i IA IA
i i IA
No, the father could not
have type O blood. IB IB
i i IB

14. Polygenic Traits Multiple genes control a single trait.
Could be any number of phenotypes, but usually a large number.
Examples:
Eye color
Hair color
Skin color
Baby weight

15. Polygenic
You will NEVER see a Punnett Square for a polygenic trait. They exist, but they are very complicated.

16. Polygenic
Instead, you will see what we call a bell curve, which shows the number of people with each level of the trait.