What are the four phases of mitosis?	Prophase, Metaphase, Anaphase, Telophase (PMAT).
How does meiosis differ from mitosis?	Meiosis has two divisions producing four haploid, genetically unique cells; mitosis has one division producing two identical diploid cells.
What happens during S phase?	The cell replicates its entire genome, forming sister chromatids joined at the centromere.
What does the G1 checkpoint assess?	Whether the cell has adequate size, nutrients, and growth factors to enter S phase. If not, the cell enters G0.
What is crossing over and when does it occur?	Exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I, increasing genetic diversity.
What is the function of the mitotic spindle?	Microtubule structure that attaches to kinetochores and separates chromosomes to opposite poles during division.
How does cytokinesis differ in animal vs. plant cells?	Animal cells use a cleavage furrow (actin/myosin contractile ring); plant cells build a cell plate from Golgi vesicles.
What is nondisjunction?	Failure of chromosomes to separate properly during division, producing aneuploid cells (e.g., trisomy 21 / Down syndrome).
What role do cyclins and CDKs play in the cell cycle?	Cyclins fluctuate in concentration and activate CDKs, which phosphorylate target proteins to drive the cell through each phase.
What is independent assortment?	Random orientation of homologous pairs at the metaphase plate in meiosis I, producing 2^n possible gamete combinations.
What occurs during prophase I?	Homologous chromosomes synapse to form tetrads, crossing over occurs, the nuclear envelope breaks down, and the spindle forms.
What is the role of p53 in cell cycle regulation?	Tumor suppressor that halts the cell cycle at G1/S when DNA damage is detected; triggers apoptosis if damage is irreparable.
What is the difference between haploid and diploid?	Diploid (2n) cells have two chromosome sets; haploid (n) cells have one. In humans: somatic = 46, gametes = 23.
What happens during anaphase II?	Centromeres split and sister chromatids are pulled to opposite poles in haploid cells.
What occurs during G2 phase?	The cell grows, synthesizes proteins for division (e.g., tubulin), and checks for DNA replication errors before entering mitosis.
How do proto-oncogenes differ from tumor suppressor genes?	Proto-oncogenes promote cell division (gain-of-function mutations cause cancer); tumor suppressors inhibit division or trigger apoptosis (loss-of-function mutations cause cancer).
What is a tetrad (bivalent)?	A group of four chromatids formed when two homologous chromosomes pair during synapsis in prophase I; site of crossing over.
What does the spindle assembly checkpoint ensure?	That all chromosomes are properly attached to spindle fibers and aligned at the metaphase plate before anaphase begins.
How does binary fission differ from mitosis?	Binary fission is prokaryotic cell division without a spindle, condensed chromosomes, or nuclear envelope. The circular chromosome replicates and the cell splits.
Why is meiosis important for sexual reproduction?	It produces haploid gametes so fertilization restores the diploid number, and generates genetic variation via crossing over and independent assortment.
What are sister chromatids?	Two identical copies of a chromosome produced during S phase, held together at the centromere by cohesin proteins until anaphase.
What is apoptosis?	Programmed cell death triggered by caspase enzymes when checkpoints detect irreparable damage, preventing proliferation of defective cells.
How does meiosis I differ from meiosis II?	Meiosis I separates homologous chromosomes (reduction division, 2n to n); meiosis II separates sister chromatids (equational division, maintains n).
What is the role of kinetochores?	Protein structures on centromeres that attach to spindle microtubules and move chromosomes toward poles during anaphase.
What are the three stages of interphase?	G1 (cell growth), S (DNA replication), and G2 (preparation for mitosis). Interphase occupies ~90% of the cell cycle.