The origin of chromosomal aberrations in man and their potential for survival and reproduction in the adult human population.

It is estimated that perhaps 20 per cent or more of all human conceptuses carry of chromosomal abnormality. This level of abnormality would appear to be higher by an order of magnitude, than that recorded for any other investigated mammalian species. Elimination by spontaneous abortion, miscarriage and peri-natal death accounts for the vast majority of chromosomally-abnormal human conceptuses. Even those individuals who survive into adulthood carrying a chromosome abnormality do so with only a limited potential to pass on their abnormality to their offspring. Some are sterilized by the chromosome abnormalities which they carry, others are mentally incapacitated and therefore excluded from the pool of reproductively active individuals. Among those who can reproduce, chromosomally normal children are usually produced since meiotic drive mechanisms which ensure a chromosomally balanced complement in egg or sperm appear to be operative.