The child inherits blood group and Rh factor from parents. Each of them transmits to the child half of the genetic information; when the paternal and maternal cells merge, a new combination of genes is formed in the embryo, which determines its group and rhesus blood affiliation.
Blood type inheritance
During the formation of germ cells during meiosis, one link of information is transmitted, and when the parental cells merge in the ovum, the information is combined into a single DNA, where each gene consists of a pair of signs. There are dominant features, i.e. suppressive and recessive - weak, which can manifest themselves only in the absence of a dominant.
The AB0 gene, which is responsible for group affiliation, is located on chromosome 9 along 34 segments. A gene may have dominants A and B or a recessive trait - 0, i.e. lack of information on the coding of glycoproteins A or B.
Parents with the first blood group have a recessive trait in the gene, i.e. 0 and such parents always transmit to their children only 0. A father or mother with the second group can have one of two sets of genetic information - AA or A0, it turns out that the child will get A or 0. The third group is determined by the set BB or B0, their child is parents will pass B or 0. But parents with the fourth blood group in their genetic code carry a set of AB, and any dominant - A or B can be passed on to their generation.
Depending on what signs merge in the gene in the child, the blood group will appear. If both parents give the baby 0, he will be with the first blood group, and the parents themselves can have I, II or III group, i.e. any, where one of the traits is 0. In cases where both parents pass trait A, or one of the parents passes A, and the other 0, the child receives the second blood group. Thus, it turns out that group II in a child can be inherited from parents with group II or from mother with group I and from dad with II or IV. The third blood group is formed when the dominant trait B is transmitted from the parents; the set of the gene can be BB or B0, i.e. the father or mother can have I group, then the other parent - III or IV, or both parents have II, IV groups. The baby can inherit the fourth group when one of the parents gives him A, and the other B, i.e. both dominants must merge. Such a genetic code is obtained when the germ cells of parents with group IV merge or when dominants from groups II and III are combined.
Rh factor inheritance
The Rh factor is determined by the dominant-recessive trait, while the positive Rh is the dominant, and the negative is the recessive trait. Depending on what genetic set the child inherited, his phenotype will appear. So, if at least one plus is present in the gene (a sign of positive rhesus), the baby will have a rhesus positive factor. But a negative rhesus can manifest itself only with the inheritance of two minuses, i.e. absolute recessive trait.
Sometimes both parents have dominant Rh positive, and the baby is born with Rh negative blood. This fact indicates that both parents are heterozygous and each of them passed on a recessive trait to the baby, which could not be manifested in the parents, because they have a second dominant sign of positive rhesus.
It often happens that a child is born with an identical blood group and Rh factor of one of the parents. But this does not mean that he inherited his father's or mother's blood. In this case, each of the parents transferred half of the information to the fetus, but it merged so that it phenotypically manifested itself as in one of the parents. For example, mom with III (BB) and dad with I (00) gave the baby set B0, and he, too, will have a third blood group like mom's, and the genetic code will be different.