1. Multiple Alleles and Genes

2. Multiple Alleles Traits usually involve only two alleles per gene
But for most genes, more than two alleles exist in a population
Existence of multiple alleles means that there may be many possible genotypes for a particular gene and many possible phenotypes

3. Multiple Genes
More commonly a trait is influenced by two or more genes
Polygenic trait – has a range of phenotypes due to the additive effects of multiple genes.
Example: skin colour and height

4. Example: Blood Types Blood Types in Humans involves 3 alleles
A person can have one of four blood types: A, B, AB or O
A person’s red blood cells may be coated with either carbohydrate A (blood type A) or carbohydrate B (blood type B), both carbohydrates (blood type AB) or neither (blood type O)

6. Blood Type (Phenotype)
There are 6 possible genotypes
There are 4 possible phenotypes
The alleles IA and IB are codominant meaning that and IA IB heterozygous individual expresses both the IA and IB traits and thus the blood type AB
Blood Type (Phenotype)
Genotype O ii A
IA IA
IAi B
IB IB
IBi AB
IA IB

7. Blood Types
If someone requires a blood transfusion it is critical that they match the recipient’s blood type with a compatible donor blood type.
The immune system detects cells that appear foreign to the body

8. Example: Someone with blood Type A has an immune system that recognizes red blood cells with carbohydrate B as foreign and will try to destroy them
Immune system proteins called antibodies will bind to the foreign carbohydrates causing the donor red blood cells to clump together

9. Someone who has blood type B has antibodies against carbohydrate A
Someone with blood type O has antibodies against both A and B carbohydrates
Refer to Figure 5.4 on Page 141
Universal Donor – “O” They can give blood to everyone
Universal Reciever – “AB” They can receive from anyone

11. Example Problem
If a man has type AB blood and a woman has type A blood, what are the possible blood types could their children have?

12. IA IB x IA IA IA IB IA IA IA IB Genotypic Ratio: 50% IA IA: 50% IA IB
Phenotypic Ratio:
50% Type A Blood: 50% Type AB Blood IA IB
IA IA
IA IB

13. IS THIS THE ONLY POSSIBLE ANSWER????
BUT WAIT!!!!!
IS THIS THE ONLY POSSIBLE ANSWER????

14. IA IB X IAi IA IB IAIA IA IB i IA i IBi Genotypic Ratio:
25% IAIA : 25% IA i: 25% IA IB : 25% IBi
Phenotypic Ratio:
50% Type A Blood: 25% Type B Blood: 25% Type AB Blood IA IB
IAIA
IA IB i
IA i
IBi

15. In Drosphila (fruit flies) there are 4 possible alleles that can be inherited for eye colour – red, apricot, honey and white.
In the case of multiple alleles, capital letters and superscripts are shown to illustrate this and the order of dominance is indicated using “>” signs.
Example: Fruit Flies

16. E1 > E2 > E3 > E4 Phenotype Possible Genotypes
E1 – red (wild) allele
E1E1, E1E2, E1E3, E1E4
E2 – apricot allele
E2E2, E2E3, E2E4
E3 – honey allele
E3E3, E3E4
E4 – white allele
E4E4
E1 > E2 > E3 > E4

17. Problem
If a wild type (red eyed) fly with E1E4 genotype is crossed with an apricot eyed fly with a E2E3 genotype, what are the probable genotypic and phenotypic ratios in the offspring?

18. E1E4 x E2E3 E1 E4 E2 E1E2 E2E4 E3 E1E3 E3E4 Genotypic ratio
Phenotypic ratio
2 red eyed: 1 apricot: 1 honey

19. Homework Multiple Alleles: Additional Problems
Using Table 1 from your note, what is the genotypic and phenotypic ratios of the following crosses?
E2E3 x E3E4 E2E4 x E3E4
E1E3 x E3E3 E2E2 x E1E4
E1E2 x E3E3 E2E2 x E3E4

20. Textbook Work Read pages 140 to 143 Page 141 # 2 & 3 Page 145 # 3, 5