title: A two-generation study of human sex-ratio variation.
abstract: We report here the first vertical population study of human sex-ratio variation. Sex-ratio data for 2 generations from Akita, Japan, have been analyzed. Parental age, birth order, sequences of the sexes at birth, and generations have no statistically significant effect on sex ratio. There is a slight excess of males at birth, as is typical for human sex-ratio studies. There is evidence of sex-ratio-dependent family planning. An analysis of vertical transmission of sex-ratio modifying factors that excludes effects of birth order in both the parental and offspring generations has detected a marginally significant paternal effect. Genetic variability of the sex ratio, if present at all, is of a very minor magnitude.
mesh_terms: D000328:Adult; D001722:Birth Order; D005193:Family Planning Services; D005260:Female; D014644:Genetic Variation; D006801:Humans; D007564:Japan; D008297:Male; D008423:Maternal Age; D010331:Paternal Age; D012743:Sex Preselection; D012744:Sex Ratio