Human X chromosome carries quantitative genes for immunoglobulin M.

Concentrations of immunoglobulin M in serum were one-third higher in females than in males in the Black and White populations of Virginia. In family studies, a much closer correlation was shown between boys and their mothers than between boys and their fathers. The immunoglobulin M concentrations in girls were more closely correlated with those of their fathers than with those of their mothers. The higher mean values for IgM in females and the relative magnitudes of the correlation coefficients between parents and offspring support the hypothesis that the X chromosome of man carries genes with an effect on IgM concentration. These patterns were not demonstrated for immunoglobulins A or G.