• There have been 5 major types of humoral antibodies named IgG, IgA, IgM, IgE and IgD.
• Antibodies are secreted by the B-lymphocytes in response to the presence of foreign substance in body.
• Variations are found in the constant regions of the antibody between individuals and this is best known about IgG antibody.
• GM factor is the variant of IgG antibody.
• IgG is only antibody which crosses the placenta and it is secreted sometimes in milk.
• When there is variation in constant region of IgG, it is treated as antigen when it crosses the placenta to baby’s body. This variation is called as Gm factor.
• Effect
> If the mother has a Gm factor not possessed by her baby, the mother’s IgG antibody will be attacked upon when the baby grows and forms its own antibody.
> However mother’s antibody which is gained through placenta or milk tends to disappear after first few years of life.
• Types of Gm factor : There are 2 types of GM factor.
(1) GM (1)+ : At position 356 – 358 they have Aspartic acid, Glutamic acid and Lucine respectively.
(2) GM (1)- : At positions 356 – 358 they have amino acids like glutamic acid, glutamic acid and methionine respectively.
• These two are produced by one locus. There have been found many such loci in different individuals.
• It has been found that different populations have been characterized by different GM characteristic.
• GM factor is an important genetic criterion for differentiation of races