Nondisjunction may occur during ________ .a. mitosisb. meiosisc. fertilizationd. both a and b

Key Concepts: Nondisjunction Explanation: Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. Step by Step Solution: Step 1. Nondisjunction can occur during mitosis and meiosis. Step 2. During mitosis, nondisjunction can lead to cells with abnormal numbers of chromosomes, which may cause genetic disorders. Step 3. During meiosis, nondisjunction can occur during the first or second division, leading to gametes with too many or too few chromosomes. Step 4. Fertilization involving a gamete with an abnormal number of chromosomes can further lead to genetic disorders, like Down syndrome. Final Answer: d. both a and b