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2.2 compare the inheritance of the ABO and Rhesus blood groups

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:

  1. If two parents, both with blood group O, have children, what are the possible blood groups of the children?
  2. gametes

    o
    o
    o
    oo
    oo
    o
    oo
    oo

    All children will have O type blood.

  3. If two parents of blood group O and AB have children, what is the possibility of having an AB type child?
  4. 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%.

  5. If one parent has A type blood and the other has B type blood, what are the possible blood types of their children?
  1. If the parents are both homozygous for the blood groups A and B:
    gametes

    A
    A
    B
    AB
    AB
    B
    AB
    AB

    100% of their children will have AB blood type.

  2. 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.

  3. If either parent is heterozygous for the blood group B:
    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.

  4. If one parent is heterozygous for blood group A and one for blood group B :
    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.

  1. If one parent is B Rh+ and the other is B Rh- and their children have B Rh+, and O Rh+ blood, what are the genotypes of the parents?
    gametes

    B-
    o-
    B+
    B+B-
    B+o-
    o+
    B-o+
    o+o-

    The parents must have Bo Rh+ and Bo Rh- genotypes.

  2. Two newborn babies were accidentally mixed up in hospital. To determine who were the parents, the blood types of the babies and the parents were taken:
    Baby 1 – O,
    Baby 2 –A,
    Mrs Brown – B,
    Mr Brown – AB,
    Mrs Smith – B,
    Mr Smith – B.
  3. From this information, it can be concluded that:

    1. the babies do not seem to belong to either family
    2. Baby 1 may be the Brown’s
    3. Baby 2 may be the Smith’s or the Brown’s
    4. Baby 1 is a Smith and cannot be a Brown.

    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