What is the phenomenon where homologous chromosomes fail to segregate properly during meiosis, leading to abnormal chromosome numbers in gametes?

💡 Solution & Explanation

Nondisjunction is the biological error wherein sister chromatids or homologous chromosome pairs fail to segregate properly during anaphase of mitosis or meiosis, resulting in abnormal gamete chromosome counts. This chromosomal aberration directly leads to conditions like Down syndrome or Turner syndrome, which are forms of genomic aneuploidy. In contrast, crossing over involves the reciprocal exchange of genetic material between non-sister chromatids during pachytene.