Final answer:
Nondisjunction is a mistake during the segregation of chromosomes, leading to gametes with an abnormal number of chromosomes and potentially causing genetic disorders.
Step-by-step explanation:
A mistake during the segregation of chromosomes is called nondisjunction. This chromosomal disorder occurs when either homologous chromosomes fail to separate during meiosis I or when sister chromatids fail to separate during meiosis II. As a result of nondisjunction, gametes can end up with an abnormal number of chromosomes, which can lead to genetic disorders if such gametes are involved in reproduction.
For instance, certain conditions like Down syndrome are a consequence of an extra chromosome 21, which is the result of nondisjunction.