1. Complex Patterns of Inheritance
Beyond Mendel’s rules of simple dominant/recessive inheritance

2. Incomplete Dominance
Neither allele is dominant; heterozygote is a blend of phenotypes of the two homozygotes.
Red + White = Pink

3. Genotype = CC; phenotype = chestnut

4. Genotype = WW; phenotype = white

5. Genotype = CW; phenotype = palomino

6. Practice incomplete dominance with Four O’Clocks (flowers)
P = RR x WW
Red parent plant R R W RW RW
White parent plant W RW RW
Genotype of F1 =
100% RW
Phenotype of F1 =
All pink!

7. R W R RR RW W RW WW F1 = RW x RW Pink parent plant Pink parent plant
Genotype ratio of F2 =
1RR : 2RW: 1WW
Phenotype ratio of F2 =
1 red : 2 pink: 1 white

8. Codominance Both alleles are dominant; expressed separately
Red + White =
Both Red and White (NOT pink!)

9. Genotype: RW

10. Genotype = RR; phenotype = red

11. Genotype = WW; phenotype = white

12. Genotype = RW; phenotype = roan

13. Show the cross between two roan cows (use R and W).
What is the probability that two roan cows will have at least one roan offspring?
50%
What is the probability that two roan cows will have a white offspring?
25% R W RR RW R W RW WW

14. Multiple Alleles More than 2 alleles possible for a trait
Example: Blood type in humans
Three alleles possible (A, B, and O), each person only has two of those alleles
Four phenotypes (blood types) possible: A, B, AB, and O
A and B are codominant; O is recessive
Alleles notated as IA, IB, i

15. Notice the new allele notation!
Type AB: IAIB Type O: ii
Type A: IAIA or IAi Type B: IBIB or IBi
Notice the new allele notation!

16. Polygenic Traits
Trait is controlled by interaction between 2 or more genes
Examples: skin color, eye color, height, hair color
Results in a continuum of expressed phenotypes

17. Lethal Recessive Alleles
Having two mutated copies of an essential gene may be deadly
E.g., Cystic Fibrosis, Sickle-cell Anemia, Tay-Sachs Disease
Heterozygote survivse because it has one nonmutated form of the gene
Heterozygote is carrier for disorder
Heterozyous condition is sometimes linked with beneficial traits
e.g., sickle cell carrier and malaria resistance

18. Other Complex inheritance patterns still to come:
Sex-linked traits
More about blood
Environmental effects
Chromosomal disorders

19. 11-3 Reading Questions What is a two-factor cross?
Draw figure 11-9 and describe what is being shown.
How many seeds were produced by the F2 generation?
Define independent assortment.
What four principals did Mendel discover?
Is it possible for some alleles to be neither dominant nor recessive?
Define incomplete dominance.
Define co-dominance.
What is erminette mean?
Define multiple alleles.
Define polygenic traits.
What reasons did Morgan have for studying Drosophila?
Finished Early?? Study Meiosis you have a quiz tomorrow