Chromosome abnormalities describe alterations in the normal number of chromosomes or structural problems within the chromosomes themselves. Both kinds of chromosome abnormalities may result from an egg or sperm with the incorrect number of chromosomes, or with a structurally faulty chromosome uniting with a normal egg or sperm during conception. Some chromosome abnormalities may occur shortly after conception. In this case, the zygote, the cell formed during conception that eventually develops into an embryo, divides incorrectly. Chromosomal abnormalities can cause serious mental or physical disabilities, and may lead to the death of the embryo. Zygotes that receive a full extra set of chromosomes, a condition called polyploidy, usually do not survive inside the uterus, and are spontaneously aborted (a process sometimes called a miscarriage).

A chromosome consists of the body's genetic material, the deoxyribonucleic acid, or DNA, along with many kinds of...