AP BIOLOGY

Detailed explanation-1: -This abrupt change in the genetic sequence of DNA is called a mutation. The replication of the DNA occurs in both mitosis and meiosis. Thus, mutations can occur during mitotic cell divisions.

Detailed explanation-2: -Mutations can occur during many points of a cell’s life cycle-during DNA replication, during Interphase as a result of some environmental factor, or during expression of DNA as cells make proteins.

Detailed explanation-3: -Importantly, new mutations also occur during meiosis, at frequencies much higher than during the mitotic cell cycles. These meiotic mutations are associated with genetic recombination and depend on double-strand breaks (DSBs) that initiate crossing over.

Detailed explanation-4: -The chromosomes are copied during interphase (prior to meiosis I). This forms two identical sister chromatids that are attached together at the centromere. During prophase I, crossing over introduces genetic variation by swapping pieces of homologous chromosomes.

Detailed explanation-5: -Common mistakes and misconceptions. Interphase is not part of meiosis. Although a cell needs to undergo interphase before entering meiosis, interphase is technically not part of meiosis. Crossing over occurs only during prophase I.