Human Blood Type Genetics - fraserscience
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
|[pic] |IB |i |
|IA |IAIB |IAi |
|i |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.
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