1. Non-Mendelian Genetics

2. Non-Mendelian Genetics
Some traits don’t follow the simple dominant/recessive rules that Mendel first applied to genetics.
Some alleles are neither dominant nor recessive.
Sometimes there are more than 2 alleles for each trait
Some traits can be controlled by more than one gene.
Sometimes traits depend on sex (M or F)

3. Incomplete Dominance
Neither allele is dominant over the other. Both alleles will be capital letters.
The heterozygous phenotype is a blending of the two homozygous phenotypes.
Example: four o’clock flowers
RR=red
WW=white
RW=pink (blending of the two alleles)

4. Practice Incomplete Dominance: Cross a red and white flower

5. Practice Incomplete Dominance: Cross two pink flowers

6. Codominance
Both alleles share dominance, so both are expressed (shown)
Both alleles are capital letters
Coat color in cows
RR: Red
WW: White
RW: Roan, white with
red spots (NOT pink!)

7. Practice Codominance: Cross a red and white cow

8. Practice Codominance: Now cross two roan cows

9. Multiple Alleles
More than two choices of alleles are present for a trait
ABO blood type has three alleles
ABO Blood types:
A and B are co-dominant (both will be displayed)
If both A and B are present, type is AB
O is recessive
Individuals can be type A, B, AB, or O (recessive)

10. Multiple Alleles (Blood Type)
6 Genotypes,
4 Phenotypes
AA – Type A
Ao – Type A
BB – Type B
Bo – Type B
AB – Type AB
oo – Type O

11. Polygenic Traits Some traits are found on more than 1 gene.
Each gene has a small effect, and all the genes together have the total effect
Examples are often traits with a wide variety (skin color, hair color, eye color)

12. Eye Color
Caused by AT LEAST two genes, with a 3rd gene suspected but not confirmed
Chromosome 15: Brown/blue gene
Chromosome 19: Green/blue gene

13. Eye Color
Multiple genes leads to many more variations / possibilities / shades / tones

14. Skin Color Located on 3 genes (A, B, C)
Maximum pigment dominant (A, B, C)
Minimum pigment recessive (a, b, c)
Darkest color (AABBCC)
Lightest color (aabbcc)
Results in:
27 genotypes
9 phenotypes

15. Skin Color Punnett Square

16. Sex-Linked Inheritance

17. Review Males have an X and a Y chromosome
Females have two X chromosomes
These chromosomes determine sex, so genes located on these chromosomes are known as sex-linked traits.

18. The X chromosome is much larger than the Y, so it carries more genes than the Y chromosome.
Disorders that are sex-linked are much more common in males, because they would only need 1 recessive allele to have the trait; rather than the two recessive alleles the females need.

19. Hemophilia Recessive trait
Disorder where individuals are missing the normal blood clotting protein.
Uncontrolled bleeds from minor cuts or bruises.
Located on X (female) chromosome
Much more common in males than females…why?

20. Hemophilia Located on X (female) chromosome
Male (XY) needs only one recessive allele
Females (XX) need both recessive alleles
If H = normal and h = hemophilia, then:
Normal Male: X(H) Y
Affected Male: X(h) Y
Normal Female: X(H) X(H)
Carrier Female: X(H) X(h)
Affected F e: X(h) X(h) – very rare

21. Red/Green Colorblindness
Inability to see the colors red and green
Located on X chromosome
If C = regular and c = colorblind, then:
Normal vision male: X(C) Y
Colorblind male: X(c) Y
Normal/non-carrier female: X(C) X(C)
Normal/carrier female: X(C) X(c)
Colorblind female: X(c) X(c)

22. A woman who is heterozygous for normal vision marries a man who is colorblind. What are the chances of them having a son or daughter who is colorblind?
**NOTE: You have to use X’s and Y’s, and read the punnett square separately for boys and girls!**

23. A woman who is heterozygous for normal vision X(C) X(c) marries a man who is colorblind X(c) Y. What are the chances of them having a son or daughter who is colorblind?

24. A woman who is homozygous for normal blood clotting X(H) X(H) marries a man who has hemophilia X(h) Y. What are the chances of them having a son or daughter with hemophilia?