Inheritance of Blood Groups

Multiple Alleles and Blood Groups

Allele
Different forms of the same gene.

Multiple Alleles
When more than two alleles control a trait these are known as multiple alleles.

Blood Groups
The alleles controlling blood groups are a well known example of multiple alleles.
There are three alleles for blood groups within the human population
A, B and o. (A and B are equally dominant and o is recessive).
Every person will have just two of these three alleles. So the possible combinations are as follows
 
Alleles  Blood Group
AA or

Ao 

A
BB or

Bo

 B
AB AB
oo
Blood groups are inherited according to simple Mendelian patterns. They are another example of a Monohybrid Cross (involving one trait only).
 

Example:

A man whose blood group is A marries a woman with blood group O. Show the possible genotypes and phenotypes of their children.
(Remember: The man can have the genotype AA or possibly Ao. The woman can only be oo
Therefore we must do out two crosses to show the possible offspring.)
 

Cross 1
Parents:  Group A  Group O
AA oo
Gametes: A  o
F1 Genotype: All Ao
Phenotype: All Group A
Cross 2
Parents: Group A  Group O
Ao  oo
Gametes: A  o  o
F1 Genotype:  Ao  oo
Phenotype:  Group A Group O
1   1

 
Following the same layout try the following cross:

Parents:                              Group AB                         Group O

Gametes: 

F1 Genotype: 

Phenotype:

Ratio:

Parents:                                     Group A                  X                                  Group B (Hint: you will have to do more than two crosses)
 
 
 

Show how two parents who both are Group A could have a child that is Group O