Through the combination of dominant and recessive genes, one coming from the father and one from the mother. It follows the same logic as that “azão” and “azinho” table we learned in school, you know? Blood types are determined based on these genes: Ia for A, Ib for B, and i for O. There is no dominance between Ia and Ib, but both are stronger than oi, which is always recessive. Each type carries two genes. AB requires one Ia and another Ib, while O needs two i. A and B can carry the classic Ia or Ib and also an i, which, after all, does not influence anything. See the tables below to better understand this crossover.
CHECK THE SIGN
We also need to determine if the blood type is going to be positive or negative.
The R gene determines the presence of the RH factor (an important antigen) and therefore a positive blood type. The r is recessive (absence of RH in the blood). Carriers of two recessive genes are RH negative. A person with RH+ can never donate blood to another RH- because the antibodies would react against the factor. For example, someone A+ cannot donate to A-.
SOURCES Sites UOL Educação, UOL Vestibular, Brasil Escola and Biologia Viva
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