1. Dominance and Multiple Allele Notes

2. Mendel’s Principles – A Review
Inheritance of traits is determined by genes.
Genes are passed from parents to offspring.
Alleles can be dominant or recessive.
In sexually reproducing organisms – each adult has two copies of each gene – one from each parent.

3. Exceptions to Mendel’s Work
Some alleles are neither dominant or recessive.
Many traits are controlled by multiple alleles or multiple genes.

4. Genetic Interactions
Incomplete dominance – When the alleles are blended and the offspring have a mix of their parent traits.
 ex. Snap Dragons
R = red
W = white
Offspring can be pink!
white

5. Genetic Interactions
Codominance – in this case both alleles are expressed.
BB= black corn
YY= yellow corn
BY = black and yellow corn
Heterozygous genotype

6. Incomplete Dominance or Codominance?

7. Incomplete Dominance or Codominance?

8. Incomplete or Codominance?

9. Polygenic Traits
A polygenic trait is determined by multiple genes. (poly=many, genic=genes)
Example: eye color and height
Skin color is controlled by more than four genes

10. Multiple Alleles Homologous chromosomes - Chromosomes occur in pairs.
(homologous means “same”)
- The different alleles of a gene occupy the same positions on each chromosome

11. Multiple Alleles
So far each gene we have discussed has been made of two possible alleles.
Ex. B = blue b= yellow
R = red r = white

12. Multiple Alleles
However, it is possible to have several different allele possibilities for one gene.
 Multiple alleles is when there are more than two allele possibilities for a gene.
Coat color in rabbits is determined by a single gene with 4 possible alleles.

13. The gene for blood type has 3 possible alleles.
Multiple Alleles
In traits with multiple alleles, each individual can carry any two of the several possible alleles.
Ex. BLOOD TYPE
The gene for blood type has 3 possible alleles.
IA, IB, and i

14. Blood Type In this case both A and B are dominant to O (recessive).
A and B are codominant (both expressed)
So... there are four human blood types
Genotype
Phenotype
IAIA, IAi
Blood type A
IBIB, IBi
Blood type B
IAIB
Blood type AB ii
Blood Type O

15. Multiple Alleles Alleles for blood type are: -IA (dominant)
-IB (dominant)
-i (recessive)

16. Blood Type Practice Problems:
1. A mother is AB and a father is O. Draw the punnett square.
IA IB i
What is the probability their offspring will have A type blood? ____
Can they have an offspring with O blood? ____

17. Blood Type
2. A mother is IAi and a father is IB IB. Draw the punnett square.
What is the probability their offspring will have B type blood?
Can they have an offspring with O blood?

18. Blood Type
3. If a child has AB blood which of the following could NOT be the parents?
a) ii, IAIB
b) IAi, IBIB
c) IBIB, IAIA
d) IAi, IBi