solve problems to predict the inheritance patterns of ABO blood groups and the Rhesus factor
compare the inheritance of the ABO and Rhesus blood groups
These two dot points are covered in the information below.
There are four ABO blood groups in humans: A, B, AB and O. The genes A and B are both dominant over the gene o, but A and B are co-dominant when both present in the same individual resulting in blood group AB. The genes for the ABO blood groups are not sex-linked.
The ABO blood groups are named from the antigens that they carry on red blood cells.
Phenotype or Blood Group Genotype Antigens present A AA A A Ao A B BB B B Bo B AB AB A and B O oo none
Examples of problems to predict inheritance of ABO blood groups:
gametes |
o
|
o
|
---|---|---|
o
|
oo
|
oo
|
o
|
oo
|
oo
|
All children will have O type blood.
gametes |
A
|
B
|
---|---|---|
o
|
Ao
|
Bo
|
o
|
Ao
|
Bo
|
There is a 50% chance of their children having A type blood and a 50% chance of them having B type blood. The possibility of having an AB type child is 0%.
gametes |
A
|
A
|
---|---|---|
B
|
AB
|
AB
|
B
|
AB
|
AB
|
100% of their children will have AB blood type.
If either parent is heterozygous for the blood group A:
gametes |
A
|
o
|
---|---|---|
B
|
AB
|
Bo
|
B
|
AB
|
Bo
|
There is a 50% chance of their children having AB blood and 50% chance of B type blood.
gametes |
A
|
A
|
---|---|---|
B
|
AB
|
AB
|
o
|
Ao
|
Ao
|
There is a 50% chance of their children having AB blood and 50% chance of A type blood.
gametes |
A
|
o
|
---|---|---|
B
|
AB
|
Bo
|
o
|
Ao
|
oo
|
There is a 25% chance of their children having each of the blood groups AB, A, B and O.
gametes |
B-
|
o-
|
---|---|---|
B+
|
B+B-
|
B+o-
|
o+
|
B-o+
|
o+o-
|
The parents must have Bo Rh+ and Bo Rh- genotypes.
From this information, it can be concluded that:
Answer: Baby 1 – oo, Baby 2 – Ao or AA, Mrs Smith – Bo or BB, Mr Smith – Bo or BB
Mrs Brown BB or Bo, Mr Brown – AB
Smiths : | Browns: |
---|---|
(i) BB x BB = only BB (B) | (i) BB x AB = BB (B) or AB |
(ii) BB x Bo = BB or Bo (B) | (ii) Bo x AB = AB or Ao (A) |
or (iii)Bo x Bo = BB, Bo (B) | or (iii) oo (O) BB, Bo (B) |
Therefore,
Baby 1 could be a Smith but definitely not a Brown;
Baby 2 could be a Brown but definitely not a Smith.
Answer: D