Image caption Bridge is played by four players who form two partnerships and involves predicting the number of tricks each side will win. Bridge players who wanted the popular card game recognised as a sport have lost their High Court battle.
Meiosis occurs in diploid cells. The chromosomes duplicate once, and through two successive divisions, four haploid cells are produced, each with half the chromosome number of the parental cell. Meiosis occurs only in sexually reproducing organisms.
The cells that form human eggs begin meiosis while the mother is herself still an embryo in the womb. But meiosis stops in the middle of prophase I, before birth, and does not resume until after the egg is released from the ovaries from 13 to 55 years later. Nondisjunction of chromosome 21 may be the result of interrupting the complicated process of meiosis for so long time.