<Tr> <Th> Specialty </Th> <Td> Medical genetics </Td> </Tr> <P> Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46 . It does not include a difference of one or more complete sets of chromosomes . A cell with any number of complete chromosome sets is called a euploid cell . An extra or missing chromosome is a common cause of genetic disorders, including some human birth defects . Some cancer cells also have abnormal numbers of chromosomes . Aneuploidy originates during cell division when the chromosomes do not separate properly between the two cells . Most cases of aneuploidy result in miscarriage and the most common extra autosomal chromosomes among live births are 21, 18 and 13 . </P> <P> Different species normally have different numbers of chromosomes from one another, and the terms aneuploid and polyploid refer to the chromosome number being different from the usual number for that species . </P> <P> Chromosome abnormalities are detected in 1 of 160 live human births . </P>

What event most commonly gives rise to aneuploids