1. Genes which have more than two alleles
MULTIPLE ALLELES
Genes which have more than two alleles

2. Multiple Alleles Another non-Mendelian pattern of inheritance
Examples are coat colours in some animals; hair colour and blood type in humans

3. Rabbit coat – 4 alleles

4. Human hair colour Expressed by multiple genes Brown/blonde gene
Red/non-red gene
Other genes for thickness, curl, and if hair darkens with age

5. The ABO blood system This is a controlled by a tri-allelic gene
It can generate 6 genotypes
The alleles control the production of antigens (protein markers) on the surface of the red blood cells
Two of the alleles are codominant to one another (IA and IB); both are dominant over the third (i)
Allele IA produces antigen A
Allele IB produces antigen B
Allele i produces no antigen

6. The ABO blood system Genotypes Phenotypes (Blood types) IA IA A IA IB
IB IB B
IBi ii O
Note:
Blood types A and B have two possible genotypes – homozygous and heterozygous.
Blood types AB and O only have one genotype each.

7. Blood types and transfusions
Blood types vary and your immune system recognises your own blood type as being self
Other blood types are recognised as non-self
If a blood which is incompatible with your body is transfused it will result in the agglutination of the foreign red blood cells

8. Antigens
© Bioformatica
© Biology Labs Online

9. Agglutination
© Dr Delphine Grézel, Ecole Nationale Vétérinaire de Lyon

10. Blood types and transfusions
People who are Type A blood produce antibodies to agglutinate cells which carry Type B antigens They recognise them as non-self
The opposite is true for people who are Type B
Neither of these people will agglutinate blood cells which are Type O Type O cells do not carry any antigens for the ABO system Type O cells pass incognito
What about type AB people?

11. Donor-recipient compatibility
Type A B AB O
Donor
Note:
Type O blood may be transfused into all the other types = the universal donor.
Type AB blood can receive blood from all the other blood types = the universal recipient.
= Agglutination
= Safe transfusion

12. Multiple Alleles
You can now continue to work on your Genetics Problems up to Set 5.
Have fun!