SUTTER The Relationship Between Human Population Genetics

~eneral terms. It might even be said that this aspect of research is frequently neglected. Blood-group experts are undoubtedly most directly responsible for this regrettable situation. Since one applies Fisher's formulas on the assumption that the blood groups are independent of age and sex, there is a tendency to confine research to any random sample of the population, which is only rarely representative of its real demographic structure. Even the disputable assumption that this approach, which is objectionable from the demographic point of view, will only rarely affect the value of the observations on blood-group frequencies hardly applies to most other spheres of genetic research. Unfortunately the students of population genetics tend all too often to adopt the methods of the blood-group experts. This procedure is questionable not only from the demographic point of view but from the genetic aspect as well. The essential feature of the problem-namely, the influence of gene frequencies-is thus neglected. Whereas the choice of the group to be studied may be of little importance in the investigation of widely distributed characters such as the ABa blood groups, for which any individual must possesstwo of the genes concerned, this is no longer true if the gene in question exists in only a few individuals-in other words, if its frequency is OJ percent or less. This is usually the casein medical genetic research, and here the sampling of the group to be studied assumes major importance. As early as 1911, S. M. Jacobi showed that the risk involved in consanguineous marriages derives precisely from the fact that the rarer a recessive gene, the higher will be the chance of encountering the affectedhomozygotes among the off;pring of consanguineous marriages. Also, the higher the frequency of cousin marriages ill the population, the larger will be their contribution to the total of affected homozygotes. Under these conditiollS, the method of sampling employed ill estimating the frequencies of carriers as well as of genes and gametes within a population assumes paramount importance. . The effect of the frequency of carriers is one of the points that Ius been most .. I i