D2.1 Cell and Nuclear Division
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What is mitosis?
Division producing 2 genetically identical diploid (2n) daughter cells; used for growth, repair, replacement, and asexual reproduction.
What is meiosis?
Division producing 4 genetically different haploid (n) gametes; introduces genetic variation for sexual reproduction.
What does diploid (2n) mean?
Cell with two complete sets of chromosomes (humans = 46).
What is the purpose of cell division?
Growth, repair, replacement of cells, asexual reproduction, and production of gametes (sexual reproduction).
What does haploid (n) mean?
Cell with one complete set of chromosomes (gametes = 23).
Why must gametes be haploid?
To restore the diploid chromosome number after fertilization.
What is the difference between nuclear division and cytokinesis?
Nuclear division = division of the nucleus (mitosis or meiosis). Cytokinesis = division of cytoplasm to form separate daughter cells.
What happens in interphase?
Cell grows, organelles replicate, DNA replicates, energy stored as ATP.
What is G0 phase?
Resting/non-dividing phase; cell may differentiate or undergo apoptosis.
What occurs during prophase - mitosis?
Chromatin condenses into chromosomes; nuclear envelope breaks down; spindle fibers form; centrosomes move to opposite poles.
What occurs during metaphase - mitosis?
Chromosomes align at the metaphase plate; spindle fibers attach to kinetochores at centromeres.
What occurs during anaphase - mitosis?
Sister chromatids separate; pulled to opposite poles by spindle fibers; ensures each daughter cell receives identical genetic material.
What occurs during telophase - mitosis?
Chromosomes decondense; nuclear envelope reforms; spindle fibers disassemble.
How does cytokinesis differ in animals vs plants?
Animals → cleavage furrow forms, membrane pinches inward. Plants → vesicles form cell plate → develops into new cell wall.
Why is mitosis energy-demanding?
Requires ATP for spindle formation, chromosome movement, and membrane reformation.
What is meiosis?
Two sequential divisions producing 4 genetically different haploid cells.
How does meiosis I differ from mitosis?
Meiosis I = reduction division, homologous chromosomes separate; genetic variation introduced via crossing over and independent assortment.
How does meiosis II differ?
Sister chromatids separate (similar to mitosis) producing haploid cells.
Prophase I - meiosis
Chromosomes condense, homologous chromosomes pair (synapsis) forming bivalents. Crossing over occurs at chiasmata → exchange of genetic material between non-sister chromatids → increases genetic variation.
Metaphase I - meiosis
Bivalents align at metaphase plate → orientation random → independent assortment occurs → increases variation.
Anaphase I - meiosis
Homologous chromosomes separate → pulled to opposite poles → reduction from 2n to n.
Telophase I and Cytokinesis - meisosis
Nuclear envelopes may form; cytoplasm divides → 2 haploid cells.
Meiosis II Stages
Prophase II: Chromosomes condense; spindle fibers form. Metaphase II: Chromosomes align at plate. Anaphase II: Sister chromatids separate. Telophase II & Cytokinesis: Nuclear envelope reforms; cytoplasm divides → 4 genetically unique haploid gametes.
What is crossing over?
Exchange of DNA segments between non-sister chromatids during prophase I → new allele combinations.