title: Influence of sex of antecedent siblings on the human sex ratio.
abstract: Analysis of family configurations in a population of 649,366 American secondary school students confirmed that sex of later-born children is influenced by the sex of antecedent siblings. Antecedent brothers decrease the probability of subsequent male births. This observation, a confirmation of an earlier report in a substantially smaller sample, is consistent with an immunologic influence on human sex determination.
mesh_terms: D002648:Child; D005191:Family Characteristics; D005260:Female; D006182:H-Y Antigen; D006801:Humans; D008297:Male; D012732:Sex Determination Analysis; D012744:Sex Ratio
chemical_list: D006182:H-Y Antigen