General principles of inheritance of characters.
Simply put, every trait in the body (hair color, eye color, blood type, Rh factor) is encoded by two genes.
In reality, the number of genes that determine the trait is much greater. For each trait, the child receives one gene from the mother, another from the father. In genetics, dominant and recessive genes are distinguished. The dominant gene is designated by a capital letter of the Latin alphabet, and in its presence the recessive gene, as a rule, does not manifest its properties. A recessive gene is indicated by a capital letter of the Latin alphabet. If for some trait an organism contains two identical genes (two recessive or two dominant), then it is called homozygous for this trait. If an organism contains one dominant and one recessive gene, then it is called heterozygous for this trait, and at the same time those properties of the trait that are encoded by the dominant gene are manifested. For example: A is a dominant gene that determines brown eye color and A is a recessive gene that determines blue eye color
Possible genotype options: AA - homozygote, brown eyes Aa - heterozygote, brown eyes aa - homozygote, blue eyes
Example 1:
wife AA - homozygous, brown eyes, both genes are dominant; husband AA - homozygous, blue eyes, both genes are recessive
When germ cells (egg and sperm) are formed, one gene goes into each germ cell (gamete), i.e. in this case, the female body forms two gametes containing one dominant gene each, and the male body forms two gametes containing one recessive gene each. When germ cells merge, the embryo receives one maternal and one paternal gene for this trait.
wife AA + husband aa Gametes: A A a a Child: Aa Aa Aa Aa
Thus, in this situation, 100% of the children will have brown eyes and be heterozygotes for this trait.
Example 2:
wife Aa - heterozygote, brown eyes husband Aa - heterozygote, brown eyes wife Aa + husband Aa gametes: A a A a child: AA, Aa, Aa, aa
In this case, the probability of having children with brown eyes (homozygotes) is 25%, heterozygotes are 50% with brown eyes, and blue eyes (homozygotes) are 25%.
Example 3:
wife Aa - heterozygote, brown eyes husband aa - homozygote, blue eyes Wife Aa + husband aa Gametes: A a a a Child: Aa, Aa, aa, aa
In this case, 50% of children have brown eyes and are heterozygotes and 50% have blue eyes (homozygotes)
What is blood type
Defining a group involves identifying an antigen of an individual nature. It directly depends on specific proteins and carbohydrates, which are localized on the membrane walls of red blood cells and in their structure.
The groups were identified by an Australian scientist who, when examining blood, discovered that on the red blood cells of different people there are various specific antigens and accompanying antibodies found in the plasma. The blood group inheritance table gives parents the opportunity to approximately determine which group their child may have.
Thus, the following four groups are distinguished:
The red blood cell membrane can contain up to three hundred different variants of determinants. These determinants are encoded at chromosomal loci by specific gene alleles. It is currently impossible to determine their exact number.
Patterns of inheritance of blood group and Rh factor.
Inheritance of blood type is controlled by an autosomal gene. The locus of this gene is designated by the letter I, and its three alleles by the letters A, B and 0. Alleles A and B are equally dominant, and allele 0 is recessive to both of them. There are four blood types. The following genotypes correspond to them: First (I) 00 Second (II) AA; A0 Third (III) BB; B0 Fourth (IV) AB
Example 1:
wife has the first blood group (00) husband has the second blood group and is homozygous (AA) wife 00 + husband AA gametes: 0 0 A A child: A0 A0 A0 A0
All children have a second blood group and are heterozygotes for this trait.
Example 2:
wife has the first blood group (00) husband has the second blood group and is a heterozygote (A0) wife 00 + husband A0 gametes: 0 0 A 0 child: A0 A0 00 00
In a given family, in 50% of cases it is possible to have a child with a second blood group, and in 50% of cases the child’s blood type will be first.
Inheritance of the Rh factor is encoded by three pairs of genes and occurs independently of the inheritance of blood type. The most significant gene is designated by the Latin letter D. It can be dominant - D, or recessive - d. The genotype of a Rh-positive person can be homozygous - DD, or heterozygous - Dd. The genotype of a Rh negative person may be dd.
Example 1:
wife has a negative Rh factor (dd) husband has a positive Rh factor and is a heterozygote (Dd) wife dd + husband Dd gametes: dd D d child: Dd Dd dd dd
In a given family, the probability of having a Rh-positive child is 50% and the probability of having a Rh-negative child is also 50%.
Example 2:
wife has a negative Rh factor (dd) husband has a positive Rh factor and is homozygous for this trait (DD) wife dd + husband DD gametes: dd DD child: Dd Dd Dd Dd
In this family, the probability of having a Rh-positive child is 100%.
Rh inheritance
It is possible to say exactly which Rh factor a child will inherit only in one case: if both parents have a negative Rh status. All offspring of this couple will be Rh negative. In all other cases, Rh can be anything.
The question arises why the Rh factor is inherited this way if both the man and the woman are Rh positive. In fact, the explanation is very simple. The fact is that positive Rh is determined by the D gene, which can have different alleles: one dominant (D), the other recessive (d). That is, a person with Rh(+) has the genotype DD (homozygous) or Dd (heterozygous). The genotype of a person with Rh(-) is designated as dd. Thus, the probability that a couple with Rh(+) will have a child with negative Rh is 25%. This can happen if both the mother and father have a heterozygous genotype - Dd. Possible Rh factor options in this case are DD, Dd, Dd, dd. Heterozygosity is caused by the birth of Rh-conflicting children in an Rh-negative woman.
You can independently determine the likelihood of offspring with a particular Rh. For example, the mother is negative, that is, she has the dd genotype, the father is positive, that is, she has the DD or Dd genotype. Possible options: Dd, Dd, Dd, dd, Dd, Dd, Dd, dd. If in this case the man is homozygous (DD), then the offspring of this couple will be Rh-positive with a probability of 100%. If a man is heterozygous (Dd), the chance of having Rh(-) in children is 50 percent.
Possible variants of the Rh factor that a child can inherit, depending on the Rh factor of the man and woman, are presented in the table below.
This is interesting: Inheritance of loans of a deceased 2020
| Mother's Rh factor | Father's Rh factor | (+) | (-) |
| (+) | any | any | |
| (-) | any | (-) |
Features of the course of pregnancy with Rh factor incompatibility. Rhesus conflict.
Hemolytic disease of the fetus and newborn is a condition that occurs as a result of incompatibility of the blood of mother and fetus for certain antigens. Most often, hemolytic disease of the newborn develops due to Rh conflict. In this case, the pregnant woman has Rh-negative blood, and the fetus has Rh-positive blood. During pregnancy, the Rh factor with the red blood cells of the Rh-positive fetus enters the blood of the Rh-negative mother and causes the formation of antibodies to the Rh factor in her blood (harmless to her, but causing the destruction of the fetal red blood cells). The breakdown of red blood cells leads to damage to the liver, kidneys, brain of the fetus, and the development of hemolytic disease of the fetus and newborn. In most cases, the disease develops quickly after birth, which is facilitated by the entry of a large number of antibodies into the baby’s blood when the integrity of the placental vessels is disrupted.
Less commonly, hemolytic disease of the newborn is caused by group incompatibility of the blood of mother and fetus (according to the AB0 system). In this case, due to agglutinogen (A or B), present in the fetal red blood cells but absent in the mother, antibodies to the fetal red blood cells are formed in the maternal blood. Most often, immune incompatibility manifests itself when the mother has blood group I, and the fetus has blood group II, and less often, blood group III.
The process of immunization of a pregnant woman begins with the formation of antigens in the red blood cells of the fetus. Since antigens of the Rh system are contained in the blood of the fetus from the 9-10th week of pregnancy, and group antigens - from the 5-6th week, in some cases early sensitization of the mother’s body is possible. The penetration of antigens into the maternal bloodstream is facilitated by infectious factors that increase the permeability of the placenta, minor injuries, hemorrhages and other damage to the placenta. As a rule, the first pregnancy in an Rh-negative woman, in the absence of previous sensitization of the body, proceeds without complications. Sensitization of the body of a Rh-negative woman is possible through transfusions of incompatible blood (carried out even in early childhood), during pregnancy and childbirth (if the fetus has Rh-positive blood), after abortions, miscarriages, and operations for ectopic pregnancy. According to the literature, after the first pregnancy, immunization occurs in 10% of women. If a woman with Rh-negative blood avoided Rh immunization after her first pregnancy, then during a subsequent pregnancy with an Rh-positive fetus, the probability of immunization again is 10%. Therefore, after any termination of pregnancy in a woman with Rh-negative blood, it is necessary to administer anti-Rhesus immunoglobulin for prophylactic purposes. During pregnancy, in a woman with Rh-negative blood, it is necessary to determine the titer of Rh antibodies in the blood over time.
What is the effect of parental heterozygosity?
With heterozygous rhesus, a woman often has problems carrying a pregnancy, since in this case the mother and child have a rhesus conflict and a specific protein rejects the fertilized egg as a foreign organism. There is a high risk of miscarriage. Inheritance of blood type and Rh factor in most cases depends on the homozygosity or heterozygosity of the parents.
The appearance of hemolytic jaundice in a child is also the cause of conflict between the blood group of the mother (in the case when the pregnant woman has the first group) and the fetus, or between the Rhesus of the mother and the child.
Question 2:
I have a negative Rh factor. I recently had an abortion. Will I be able to have children? Is there a chance that the baby will be sick during the next pregnancy?
Answer
: The presence of a negative Rh factor does not directly affect conception. During an abortion (if it was performed at 9-10 weeks of pregnancy), there was a possibility of sensitization of the body to the Rh factor. Before a planned pregnancy, it is advisable to do a blood test for the presence of antibodies to the Rh factor.
Question 3:
What dose of anti-Rhesus immunoglobulin and in what time frame is administered to a woman with Rh-negative blood after childbirth? Is it true that the administered dose of the drug should be increased after a caesarean section?
Answer
: Women with Rh-negative blood after childbirth are given anti-Rhesus immunoglobulin in an amount of 1-1.5 ml (200-300 µg) no later than 24-48 hours after birth for prophylactic purposes. During surgical interventions, transplacental bleeding may increase, and therefore the administered dose of anti-Rhesus immunoglobulin is increased by 1.5 times.
