The Chromosome Number Affected

Chromosome 21

The chromosome number that Down Syndrome is caused by is Chromosome 21 or Trismoy 21

~Complete trisomy 21- when the egg or sperm holds the extra chromosome, 95% of Down Syndrome cases

~Mosaic trisomy 21- most cells in the body hold the extra chromosome,but some don't, 1% of Down Syndrome cases

~Translocation trisomy 21- only one part of the extra chromosome is in the cells, 4% of Down Syndrome cases