MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedoniuk 2010

BIOLOGY

CHAPTER 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.2. Basics of human genetics

Inheritance of the Rhesus Factor

The rhesus (Rh) factor is a protein (antigen) named so because it was first isolated (in 1940) from the erythrocytes of the rhesus macaque monkey (Macacus rhesus) and later in humans. About 85% of Europeans are able to synthesize it and constitute the Rhesus-positive group (Rh+), while 15% are unable to do so and are called Rhesus-negative (Rh-). The rhesus factor is determined by three dominant closely linked genes (C, D, E) located on the first chromosome. They are inherited as in Monohybrid Crosses. The primary role belongs to the D antigen; if it is detected, the Blood is Rhesus-positive (DD or Dd), and if it is not detected, it is Rhesus-negative (dd). The rhesus factor must be taken into account during blood transfusions and organ transplantation because the body produces Antibodies against it. The rhesus factor can be the cause of an Rhesus incompatibility conflict between mother and fetus. If an Rhesus-negative woman marries a man who is Rhesus-positive homozygous, all children will be Rhesus-positive; if he is heterozygous, 50% will be Rhesus-positive and 50% Rhesus-negative (Fig. 1.67).

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Fig. 1.67. Genetic diagrams illustrating the inheritance of the rhesus factor.

The conflict arises when the mother has Rhesus-negative blood, while the child has inherited the dominant D allele from the father and is Rhesus-positive. The blood of the mother and the fetus does not mix, so the first Pregnancy usually proceeds normally. However, during the birth of the first child, when the Placenta detaches, the child's erythrocytes enter the maternal Circulation, triggering The production of antibodies against the rhesus antigen. During a subsequent pregnancy, these antibodies cross the placental barrier into the fetal bloodstream, bind to the rhesus antigen, and cause erythrocyte agglutination and lysis (erythroblastosis fetalis, or hemolytic disease of the newborn). Furthermore, with each successive delivery, the severity of the disease in children increases. If an Rhesus-negative girl receives a transfusion of Rhesus-positive blood prior to marriage, even her first child (if Rhesus-positive) will be unviable. Therefore, even a single transfusion of Rhesus-positive blood to girls with Rhesus-negative blood is strictly prohibited.

Hemolytic disease of the newborn was described over 400 years ago. It occurs due to incompatibility not only in the rhesus system, but also in the ABO system—most frequently when the mother has blood group I (0) and the child has group II (A) or III (B).