Distribution of M and N blood groups

Paleoserology

See Also

• [MNS Blood Group]?

Description

The M and N [Allelomorph? allelomorphs] were discovered in 1927. (1) These letters represent inherited antigens, detectable in human blood by the use of agglutinins formed by rabbits injected with M positive (or N positive) human red cells. These antigens have been reported by some to be present in tissues other than red cells, but other workers have not found them outside the blood. Each human being has two of these genes, either two M genes, two N genes, or one of each; three types are thus determined, as shown in Table 1.

Unlike the A, B groups, the M and N blood types, as they are called, have but little importance in the performance of blood transfusions, since agglutinins capable of reacting specifically with these antigens are rarely if ever found in normal human blood. This lack of medical importance has somewhat limited the amount of information which we have about this newer gene series, since investigations by medical men have been, so far at least, the chief source of data concerning blood groups. But enough is known to make possible the outline which is shown in the accompanying map. For example, the M and N frequencies are quite well known for the native inhabitants of one whole continent, Australia, and for some adjacent populations. (See Fig. 1.) Since only two genes are involved and the sum of their frequencies must equal unity, to give an adequate picture it is suflcient to plot the frequency of either gene alone, and we have shown here the frequency of the gene M.

FIGURE 1. Frequencies of blood group gene M in Australia and regions to the north (after Graydon and Simmons).

In Table 2, M and N gene frequencies for the whole world are shown. If we ignore certain slight variations in small groups of people who have been tested in Europe and Asia, we can make the following general statement: the genes M and N are roughly of equal frequency in both Europe and Asia but in the aborigines of America the gene for N is relatively rare. In the aborigines of Australia, as we have seen, however, the gene for N is very common, while the gene M is very rare, and it is even possible that in certain earlier times, the gene, though probably originally present, was totally lost by certain populations in Australia (2), presumably by 'random genetic drift'.

The A and B, M and N factors in human blood still by no means exhaust the list of antigenic differences which have been found in normal human blood. Subgroups of A (3) and probably of B exist. Subgroups of N have been reported. We shall discuss the sub.. groups later in this chapter. The inheritance of these subgroups is not quite so well established as that of the main groups (4, 5). Also factors designated by the letters P, G, H, X, Q, E, and Rh have been described by various workers (6, 7). More recently English workers (8), (9), 10) have discovered other previously unknown blood grouping factors. It is known that racial differences exist in the frequencies of these other blood grouping factors and that the factor P, for instance, is much more common in the blood of Negroes, or at least American Negroes, than in the blood of American whites. The other factors, with the exception of Rh, have not yet been sufficiently studied to have any value in anthropological classification.

Distribution in Finnish Lapps

Most Finnish Lapp populations have over 5o per cent of N genes; the Norwegian and Swedish Lapps have a higher frequency of the NS haplotype than any known populations except the Ainu. In the Rh system they have one of the lowest d frequencies in Europe, and they have about 12 per cent of the otherwise rare CvDe haplotype, which they appear to have passed on to their Scandinavian neighbours. The Lapps thus differ widely from all oth;r known populations, with a tendency towards Asiatic values for some characters (high Fya and PTC taster gene) but not for others (ABO, MNSs). Their origins and relationships are thus something of a mystery, and it has even been suggested that they are descended from a population which survived the last ice age isolated in an unglaciated area (which certainly existed) in the extreme north of Norway, beyond the great European icesheet.

It has, however, recently become possible to make limited blood group comparisons with another group of Finno-Ugric speakers, the Samoyeds, reindeer herders who migrated eastward into the north-western parts of Asiatic Russia. These have rather low frequencies of A and high of B, but they do resemble the Lapps in having exceptionally high frequencies of N and they could thus conceivably provide a connecting link between the otherwise isolated Lapps and Ainu, both also with very high N.(11)

Attribution

From: Genetics And The Races of Man, William C. Boyd. Little Brown and Company, Boston (1950)

References