Practice question

Meiosis consists of two divisions following single S phase, with meiosis II equationally separating sisters after reductional meiosis I segregated homologs. Cells exit meiosis I entering interkinesis without replication, centrosomes duplicate, chromosomes recondense, and spindle reforms often orthogonal to first division axis. At metaphase II plate, sister chromatids align with kinetochores bioriented to opposite poles similar to mitosis, achieved despite haploid chromosome number. Protection of centromeric cohesion established in meiosis I by Shugoshin SGO2 bound to PP2A phosphatase that dephosphorylates Rec8 cohesin preventing separase cleavage is now removed as SGO2 degrades from centromeres. Upon APC/C-Cdc20 activation at anaphase II, securin degraded, separase active cleaves remaining centromeric Rec8, dissolving cohesion. Sister chromatids, now genetically non-identical due to crossing over in prophase I exchanging non-sister segments, separate toward opposite poles driven by kinetochore microtubule depolymerization and spindle elongation, generating four haploid daughter cells essential for sexual reproduction and complementation after fertilization. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.