There are many blood types of people, and each blood type system is determined by heredity and has immunological characteristics. The most common blood group system is ABO blood group system, which is divided into four types: A, B, AB and O. The inheritance of blood group depends on chromosomes in cells. There are 23 pairs of chromosomes in human cells, and each pair of chromosomes consists of two chromatids, one from the father and the other from the mother.

Blood type is determined by the genetic genes given by parents to their children, but it does not mean that parents are blood type, and children are also blood type, because the combination of genes will be different. For example, a mother with blood type AB may pass on the A gene to her first child and the B gene to her second child. This is a random process, so brothers and sisters may have different blood types.

Most of them can judge the possible blood types of future babies according to their parents' blood types.

Extended data:

A small piece of DNA in the same position on two single chromosomes in a pair of chromosomes is called allele. The gene locus of ABO blood group system is located on chromosome 9. ABO blood group is controlled by three genes: A, B and O, and one * * can be combined into six pairs of alleles: AA, AO, BB, BO, AB and OO.

ABO blood group has six pairs of alleles, so there are six genetic models. For example, the genetic patterns of the above two cases are AA and AO respectively. There are only four common ABO blood types: AA, BB, AB and OO. This is because blood type actually refers to its expression. Not all inherited genes can be expressed, and the traits that can be expressed are called expression.

The difference between the expression of blood type and heredity is that there are dominant genes and recessive genes. In ABO blood group system, A and B genes are dominant genes, and O genes are recessive genes. For example, in a pair of chromosomes, one chromosome carries the A gene and the other chromosome carries the O gene. The allele combination is AO, the genetic formula is AO, and the expression is A. This person's blood type is A, not O.

Both parents are type A, so it can be inferred that both father and mother have the possibility of inheritance of AA and AO blood types. If both parents' chromosomes carry O gene when the child is born, then the allele combination of the child's chromosome is OO, inherited as OO and expressed as O, that is, the child's blood type is O type.

Baidu Encyclopedia-Blood Group Genetic Rules Table

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