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View Full Version : Why trisomy has 47 chromosomes? Mamona 08-07-2008, 12:40 PM I don't get this, I know that in the case of Down Synd. trisomy 21 we have 3 chromosomes at chromosome 21, but we also have another chromosome that doesn't have a pair b/c it moves with chromosome 21..... I don't know why I can't picture the 47 chromosomes can somebody help me with this....:confused: tranv117 08-07-2008, 12:47 PM In a normal person, theres 23 pairs of chromosomes, making it 46 chromosomes total. In trisomy 21, you have an extra chromosome making it 47 chromosomes total. I believe that extra chromosome comes from nondisjunction during meiosis. doc3232 08-07-2008, 01:11 PM Picture it like this...you see 22 chromosome pairs and then this group of 3 sitting together that don't fit in with the rest. Mamona 08-07-2008, 01:28 PM thank you guys Contach 08-07-2008, 01:38 PM thank you guys the key above was meiosis... so you have a germ cell that is diploid (lets say a progenitor sperm cell) 46 chromosomes undergoes meiosis will produce 2 new sperm 1 with 23 chromosomes and another with 23 chromosomes these will go off and fertilize an egg. producing a normal baby. in the case of trisomy.. this is what happens. 46 chromosomes undergoes meiosis, but with a nondisjunction (one pair didn't split properly) will produce 2 new sperm 1 with 22 chromosomes and another with 24 chromosomes these will go off and fertilize an egg. if the 1 with 22 chromosomes fertilizes, you may get downs syndrom (22+23 =45)(or another type of monosomy), if the sperm with 24 chromosomes makes it to the egg first, you may get trisomy 21 (24+23=27) (or another type of trisomy disease). Mamona 08-07-2008, 02:20 PM the key above was meiosis... so you have a germ cell that is diploid (lets say a progenitor sperm cell) 46 chromosomes undergoes meiosis will produce 2 new sperm 1 with 23 chromosomes and another with 23 chromosomes these will go off and fertilize an egg. producing a normal baby. in the case of trisomy.. this is what happens. 46 chromosomes undergoes meiosis, but with a nondisjunction (one pair didn't split properly) will produce 2 new sperm 1 with 22 chromosomes and another with 24 chromosomes these will go off and fertilize an egg. if the 1 with 22 chromosomes fertilizes, you may get downs syndrom (22+23 =45)(or another type of monosomy), if the sperm with 24 chromosomes makes it to the egg first, you may get trisomy 21 (24+23=27) (or another type of trisomy disease). I got the whole picture now, thanks!!! |