1. Multiple Alleles
Three or more alleles of the same gene that code for a single trait.
ABO & Rh blood groups are examples

2. Blood type alleles A, B, O A & B are co dominant
Either A or B, or both, are dominant over the O allele.
O is recessive

3. Rh alleles
Rh comes from rhesus monkey, the model being studied for blood types.
+ and – are the common ones that determine the trait

4. ABO system -
Classifies blood according to antigens present on the erythrocytes (RBCs).
May carry A, B, AB or O
A & B are codominant; both are dominant over O.

5. Blood chart AB IAIB (AB) A,B O ii (OO) none
Phenotype Genotype Antigen on RBC
A IAi or IAIA (AO< AA) A
B IBi or IBIB (BO, BB) B
AB IAIB (AB) A,B
O ii (OO) none

6. Rh factor 85% of population is Rh+; 15% is Rh-
If Rh factors mix, the blood agglutinates.
Problem – Rh- mother and Rh+ father
Condition - Erythroblastosis fetalis
Solution: