Download Human Blood Type Genetics

Human Blood Type Genetics
Most blood group genes are co-dominant. For example, in the ABO system, A
and B genes are co-dominant.
Many blood group antigens are indirect gene products. For example, A and B
antigens are carbohydrates. Their genes produce proteins (enzymes) called
transferases which transfer sugars from carrier molecules to acceptor molecules.
Usually if a gene is present, its corresponding antigen will be present.
Almost all blood group genes are inherited on the autosomes.
A Punnett Square is used to determine the inheritance possibilities for a
particular mating. For example if the mother's genotype (genes) are IAi and
the father's genotype (genes) are IBi, you would have the following Punnet
square possibilities.
In this example there three heterozygous possibilities AB, AO, and BO and one
homozygous possibility OO
IB
IA
i
i
IAIB IAi
IBi ii
In the above Punnett Square, the AB genotype will have both A and B antigens,
therefore the phenotype is AB since both are expressed. AO and BO genotypes
will demonstrate only the A and the B antigens respectively and therefore the
phenotypes are A and B respectively. The individual that is OO will have the O
phenotype.
A and B genes are dominant, or co-dominant, and the O gene is recessive. The
dominant genes will be expressed if present. Recessive genes will only be
expressed if they are homozygous.
Most Blood Group genes are co-dominant and therefore will be expressed if
present.