title: The transition in frequency of Y-chromatin in males during early infancy.
abstract: The frequency of Y-positive lymphocytes in blood smears at delivery and during early infancy was assessed to determine the exact time at which it is similar to the frequency in adults. It was found that at day 0 of life the frequency of Y-chromatin-positive cells was 26.6 +/- 13.2% (mean +/- SD); subsequently, it increased gradually to 41.2 +/- 12.2%, 49.7 +/- 9.7% and 55.4 +/- 5.2% at the 30th day, the end of the 3rd month and the end of the 4 month of life, respectively (Fig. 1). The frequency in adult males was 57.8 +/- 5.8%. This is the first time that the same infant population has been investigated in all the stages of a study.
mesh_terms: D000328:Adult; D000367:Age Factors; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008214:Lymphocytes / Q000648:ultrastructure; D008297:Male; D012016:Reference Values; D012728:Sex Chromatin / Q000032:analysis*; D012732:Sex Determination Analysis