B Sc III Blood group inheritance


Source : http://webcache.googleusercontent.com/search?q=cache:http://www.nzblood.co.nz/give-blood/about-blood/inheritance-of-blood-groups/&gws_rd=cr&ei=-qpzVr7zGIaSuAS95afQAw

 Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three types of allelesinferred from classical genetics: i, I^A, and I^B. The gene encodes aglycosyltransferase—that is, an enzyme that modifies thecarbohydrate content of the red blood cell antigens. The gene is located on the long arm of the ninth chromosome (9q34).

The I^A allele gives type A, I^B gives type B, and i gives type O. As bothI^A and I^B are dominant over i, only ii people have type O blood. Individuals with I^AI^A or I^Ai have type A blood, and individuals with I^BI^Bor I^Bi have type B. I^AI^B people have both phenotypes, because A and B express a special dominance relationship: codominance, which means that type A and B parents can have an AB child. A couple with type A and type B can also have a type O child if they are both heterozygous (I^Bi,I^Ai) The cis-AB phenotype has a single enzyme that creates both A and B antigens. The resulting red blood cells do not usually express A or B antigen at the same level that would be expected on common group A₁ or B red blood cells, which can help solve the problem of an apparently genetically impossible blood group.^[22]

Blood group inheritance
Blood type		O	A		B		AB
	Genotype	ii (OO)	IAi (AO)	IAIA (AA)	IBi (BO)	IBIB (BB)	IAIB (AB)
O	ii (OO)	O OO OO OO OO	O or A AO OO AO OO	A AO AO AO AO	O or B BO OO BO OO	B BO BO BO BO	A or B AO BO AO BO
A	IAi (AO)	O or A AO AO OO OO	O or A AA AO AO OO	A AA AA AO AO	O, A, B or AB AB AO BO OO	B or AB AB AB BO BO	A, B or AB AA AB AO BO
	IAIA (AA)	A AO AO AO AO	A AA AO AA AO	A AA AA AA AA	A or AB AB AO AB AO	AB AB AB AB AB	A or AB AA AB AA AB
B	IBi (BO)	O or B BO BO OO OO	O, A, B or AB AB BO AO OO	A or AB AB AB AO AO	O or B BB BO BO OO	B BB BB BO BO	A, B or AB AB BB AO BO
	IBIB (BB)	B BO BO BO BO	B or AB AB BO AB BO	AB AB AB AB AB	B BB BO BB BO	B BB BB BB BB	B or AB AB BB AB BB
AB	IAIB (AB)	A or B AO AO BO BO	A, B or AB AA AO AB BO	A or AB AA AA AB AB	A, B or AB AB AO BB BO	B or AB AB AB BB BB	A, B, or AB AA AB AB BB

The table above summarizes the various blood groups that children may inherit from their parents.^[23][24] Genotypes are shown in the second column and in small print for the offspring: AO and AA both test as type A; BO and BB test as type B. The four possibilities represent the combinations obtained when one allele is taken from each parent; each has a 25% chance, but some occur more than once.

Blood group inheritance by phenotype only
Blood type	O	A	B	AB
O	O	O or A	O or B	A or B
A	O or A	O or A	O, A, B or AB	A, B or AB
B	O or B	O, A, B or AB	O or B	A, B or AB
AB	A or B	A, B or AB	A, B or AB	A, B or AB

Historically, ABO blood tests were used in paternity testing, but in 1957 only 50% of American men falsely accused were able to use them as evidence against paternity.^[25] Occasionally, the blood types of children are not consistent with expectations—for example, a type O child can be born to an AB parent—due to rare situations, such as Bombay phenotype and cis AB.^[26]

Source https://en.wikipedia.org/wiki/ABO_blood_group_system