Researchers have discovered a key tool that helps sperm and eggs develop exactly 23 chromosomes each, a finding that could lead to insights into fertility, cancer, and developmental disorders. Healthy humans have 46 chromosomes, 23 from the sperm and 23 from the egg. An embryo with the wrong number of chromosomes is usually miscarried, or develops disorders such as Down syndrome, which is caused by an extra copy of chromosome 21.
