What is a key consequence of nondisjunction during meiosis?

What is a key consequence of nondisjunction during meiosis?

• A. Normal segregation with no aneuploidy.
• B. DNA replication occurs.
• C. RNA processing increases.
• D. Failure of homologous chromosomes or sister chromatids to separate during meiosis, leading to aneuploidies such as trisomies or monosomies.

Answer: (D)

Nondisjunction during meiosis is the failure of separation of homologous chromosomes or sister chromatids, resulting in gametes with an abnormal chromosome number. When such a gamete fertilizes a normal one, the zygote often becomes aneuploid, carrying an extra chromosome (trisomy) or missing one (monosomy). This direct outcome explains why conditions like trisomy 21 or monosomy X arise. The other ideas—DNA replication happening or RNA processing increasing—aren’t consequences of mis-segregation in meiosis, and normal segregation would avoid producing aneuploid gametes.

Nondisjunction during meiosis is the failure of separation of homologous chromosomes or sister chromatids, resulting in gametes with an abnormal chromosome number. When such a gamete fertilizes a normal one, the zygote often becomes aneuploid, carrying an extra chromosome (trisomy) or missing one (monosomy). This direct outcome explains why conditions like trisomy 21 or monosomy X arise. The other ideas—DNA replication happening or RNA processing increasing—aren’t consequences of mis-segregation in meiosis, and normal segregation would avoid producing aneuploid gametes.