This document discusses multiple alleles and blood types. It defines genes and alleles, noting that most genes have two alleles but some have three or more, called polyallelic genes. The ABO blood type system is controlled by a triallelic gene that generates six possible genotypes based on three alleles that determine the A, B, and O antigens. Blood transfusions require matching blood types to avoid agglutination, as the immune system recognizes foreign blood types.

1. MULTIPLE ALLELE
& BLOOD TYPES
BY: MRS. PRECILLA C. STEPHEN

2. DEFINITION
• Genes are particularly region of DNA that control a specific trait such as
tongue rolling or ear lobe.
• An allele is one of the possible forms of gene. Most genes have two alleles, a
dominant allele and a recessive allele. An allele which consists of three or
more alleles of the same genes.
• However, individuals within the population are only able to hold two of
them.

3. GENES AND THEIR ALLELES
• About 30% of the genes in humans are di-allelic, that is they exist in two
forms, (they have two alleles)
• About 70% are mon-allelic, they only exist in one form and they show no
variation.
• A very few are poly-allelic having more than two forms.

4. COMBINATIONS
• Di-allelic genes can generate 3 genotypes
• Genes with 3 alleles can generate 6 genotypes (3+2+1)
• Genes with 4 alleles can generate 10 genotypes
• Genes with 8 alleles can generate 36 genotypes.

5. THE ABO BLOOD SYSTEM
• This is controlled by tri-allelic gene. It can generate 6 genotypes:
The alleles control the production of antigens on the surface of the RBCs.
Two of the alleles are codominant to one another and both aer dominant
over the third.
Allele IA produces antigen A
Allele IB produces antigen B
Allele I produces no antigen

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

8. AGGLUTINATION

10. O- O+ A- A+ B- B+ AB- AB+
O- 
O+  
A-  
A+    
B-  
B+    
AB-    
AB+        