Fluorescent Y chromatin in newborn males

In two independent series, the frequency of Y chromatin, visualized as fluorescent bodies in cell nuclei from the buccal mucosa was significantly less in newborn males than in adult males. The frequency rose steadily during the first 5 days of life, attaining the mean adult level by day 3. Analysis of variance over the first 5 days indicated a significant change from day to day. The increasing frequency of fluorescent bodies during the neonatal period is similar to that of X chromatin and may be influenced by similar factors. These findings are clearly relevant to any instance in which this investigation is to be undertaken in the newborn period, and especially when XO/XY mosaicism is being considered.