The ABO blood group is controlled by a single gene
(the ABO gene) with three types of allele inferred from classical genetics: i,
IA and IB. the gene encodes a gylcosyltransferase – that
is an enzyme that modifies carbohydrates content of the red blood cell antigen.
The gene is located on the long arm of the ninth chromosome – The IA
allele gives type A, IB gives type B and i gives type O. the A and B
allele are dominant over O. The A and B allele are also co-dominant. Therefore
if an A type is inherited from one parent and a B type from the other, the
phenotype will be AB (Yazer et al., 2006).
(the ABO gene) with three types of allele inferred from classical genetics: i,
IA and IB. the gene encodes a gylcosyltransferase – that
is an enzyme that modifies carbohydrates content of the red blood cell antigen.
The gene is located on the long arm of the ninth chromosome – The IA
allele gives type A, IB gives type B and i gives type O. the A and B
allele are dominant over O. The A and B allele are also co-dominant. Therefore
if an A type is inherited from one parent and a B type from the other, the
phenotype will be AB (Yazer et al., 2006).
Genetic Terms
i.
Gene: Determines specific
inherited traits (e.g. blood types).
ii.
Chromosomes: Unit of inheritance
carries the gene. They are 23 pairs of chromosomes per person, one from mother,
other inherited from father.
iii.
Locus: Site on Chromosome where
specific gene is located.
iv.
Allele: alternative choice of gene
at a locus, e.g. A or B.
v.
Homozygous: Allele are the same for
any given trait on both chromosomes, e.g. A/A.
vi.
Heterozygous: Allele for a given trait
is different on each chromosome e.g. A/B or A/O.
vii.
Phenotype: Observed inherited trait
(e.g. group A or Rh positive).
viii.
Genotype: Actual genetic information
for a trait carried on each chromosome e.g. A/O type as A.
Genotype: Actual genetic information
for a trait carried on each chromosome e.g. A/O type as A.
ix.
Dominant: The expressed characteristics
on one chromosome take precedence over the characteristics determined on the
other chromosome, e.g. A/O type as A.
x.
Co-dominant: The characteristics determined
by the gene on both chromosomes are both expressed, neither is dominant over
the other (e.g. A/B types as AB).
xi.
Recessive: The characteristics determined by the alleles
will only be expressed if the same allele is on the other chromosome also
(Genotype O/O as type O).
