Abnormal chromosome structure in early human embryos is quite common, according to a report online this week in Nature Medicine. This high rate of chromosomal instability in early embryos could account for the relatively low fertility rate, and higher than expected miscarriage rate, in humans.
Chromosomal instability is characterized by duplications, deletions, or translocations of whole chromosomes, or of pieces of chromosomes. Joris Vermeesch and colleagues analyzed the genome of 23 early embryos from young women who were undergoing in vitro fertilization, and found that only 2 of them had chromosomes that were completely normal. The chromosomal alterations that the researchers identified in the other 21 embryos were likely due to errors that arose during cell division.