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

2. Beyond Mendel
The law of independent assortment holds true for all genes unless the genes are linked.
If the genes are in linked they do not independently segregate during gamete formation, usually because they are close to each other on the same chromosome.

3. Gene Linkage & Crossing Over
Gene linkage - genes that are located on the same chromosome will be inherited together. These genes travel together during gamete formation
Crossing-over is a process in which alleles in close proximity to each other on homologous chromosomes are exchanged during Prophase I on Meiosis I.
Crossing-over explains how linked genes can be separated resulting in greater genetic diversity that could not be explained by Mendel’s principles of genetics.

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

5. Parent One: Genotype = CC; phenotype = chestnut

6. Parent Two: Genotype = WW; phenotype = white

7. Offspring: Genotype = CW; phenotype = palomino

8. 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!

9. 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

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

11. Genotype: RW

12. Genotype = RR; phenotype = red

13. Genotype = WW; phenotype = white

14. Genotype = RW; phenotype = roan

15. 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

16. 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

17. 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!

18. 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

19. 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 survives 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

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