BLOOD GROUP INHERITANCE
Blood groups their role In Inheritance
Karl Landsteiner(1900) observed different types of Blood groups in Man. The chief blood groups in men are ‘A’, B, ‘AB, and ‘0’. Besides these blood groups of Men, eighty-two human blood group
Phenol types have been discovered from 1900 to 1965 by different scientists. Extensive studies have shown that there are two types of substances in the blood known as ‘antigens’ or ‘agglutinogens’ and ‘antibodies’ or agglutinins’ Antigens are designated by the English alphabets A and B The antigens are present in the erythrocytes (R.B.C) and antibodies (ab) in the blood plasma. Usual, if a person has an antigen iii his erythrocytes his plasma has natural antibodies against the other antigen. For example, a person having antigen-A in the erythrocytes, has antibody-b’ in his plasma. Recent chemical investigations reveal that antigens A and B are not proteins but muco polysaccharides (sugars + amino acids).
Depending upon the presence and absence of antigens and antibodies the following four blood groups have been differentiated.
The persons of 0 - group can give blood to all but can receive only from his own group. Hence, these persons are known as ‘universal donors’. The 0 - blood group lacking antigens and not clumped by the serum of any blood group. AB - blood group does not cause clumping of corpuscles of any group. Hence these persons can receive blood from the persons of all the blood groups. So they are known as ‘Universal recipients’, but can donate blood to the persons of their own group. Terms universal donor and
universal recipient are no longer applicable after the discovery of
Rh factor. The following table can give the possible effects of transfusion of blood and the possible genotypes of individuals with different types of blood groups.
In 1925 Bernstein discovered that the inheritance of different blood groups in man is determined by a number of multiple allelic series. There are alleles concerned with the determination of blood group of any person. The Blood groups and genotypes of parents and offspring’s are given below.
For convenience group 0’ is regarded as normal and alleles ‘A’ and ‘B’ are said to represent two dominant mutations which are present on the same locus. These represent co dominant alleles. If normal gene is represented by +, the three genes will be +, and . Since + is recessive, individuals of group 0’ will have a genotype +1+ ; gene ‘A’ is dominant, individual of blood groups ‘A’ might have a genotype either +/A or NA. Similarly individuals of group ‘B’ might have +1 B or B/B and individuals of group AS will has genetic composition N B. The given table shows the results of crosses between the individuals of different genotypes.