What mutation refers to those chromosomes that are either missing or have extra copies, such as in Down Syndrome?

The mutation that refers to chromosomes that are either missing or have extra copies is known as a nondisjunction mutation. This type of mutation occurs during cell division, specifically during meiosis, when chromosomes do not segregate properly. As a result, one gamete may receive two copies of a chromosome, while another gamete receives none. This improper segregation can lead to conditions such as Down syndrome, which is caused by the presence of an extra copy of chromosome 21 (trisomy 21).

The significance of nondisjunction lies in its ability to alter the normal chromosomal number in an organism, leading to genetic disorders. Understanding this mechanism is crucial in genetics, as it highlights how chromosomal abnormalities arise and can lead to various phenotypic outcomes.