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Trisomy |
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Meiosis
is the name used to describe the cell division that the egg and
sperm go through when they are developing. Normally, meiosis causes
a halving of chromosome material, so that each parent gives 23 chromosomes
to a pregnancy.The result is an egg or sperm with only 23 chromosomes.
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When fertilization occurs, the normal 46 total number of chromosomes results. If meiosis does not occur properly, an egg or sperm could end up with too many chromosomes, or not enough chromosomes. Upon fertilization, the baby could then receive an extra chromosome (called a trisomy), or have a missing chromosome (called a monosomy):
