Cell Cycle and Cell Division - Meiosis and Mitosis (Vocabulary)

Vocabulary flashcards covering key terms from mitosis and meiosis as described in the lecture notes.

Telophase II

The final phase of meiosis II in which chromatids reach the poles, decondense, spindle fibers degenerate, and the nuclear membrane and nucleolus reappear; four haploid nuclei are formed and cytokinesis follows to produce four haploid cells.

Meiosis II

Second meiotic division (equational division) that separates sister chromatids in haploid cells; no DNA replication occurs between meiosis I and II, resulting in four haploid daughter cells.

Cytokinesis

Division of the cytoplasm following karyokinesis; in animals by a contractile furrow and in plants by the formation of a cell plate.

Prophase II

Short phase where chromatid condensation occurs again, the nucleolus and nuclear envelope disappear, and the spindle apparatus forms.

Metaphase II

Univalents align at the equator; kinetochores attach spindle microtubules from opposite poles.

Anaphase II

Centromeres split and sister chromatids separate, moving to opposite poles as chromatids become chromosomes.

Prophase I

Elaborate, prolonged stage subdivided into leptotene, zygotene, pachytene, diplotene, and diakinesis; chromosomes condense and homologous chromosomes pair (synapsis) with crossing over.

Leptotene

First substage of prophase I; chromatin condenses and chromosomes become visible as thin threads.

Zygotene

Second substage; homologous chromosomes begin pairing (synapsis) to form bivalents aided by the synaptonemal complex.

Pachytene

Third substage; chromosomes thicken, form tetrads, and crossing over between non-sister chromatids occurs, creating recombination.

Diplotene

Crossing over completed; homologs begin to separate but remain attached at chiasmata; synaptonemal complex dissolves.

Diakinesis

Final stage of prophase I; spindle forms, chiasmata terminalize, nucleolus disappears, and nuclear envelope breaks down.

Synapsis

Pairing of homologous chromosomes during prophase I to form bivalents.

Synaptonemal complex

Protein structure that stabilizes the pairing (synapsis) of homologous chromosomes during prophase I.

Crossing over

Exchange of genetic material between non-sister chromatids of homologous chromosomes, increasing genetic variation.

Chiasmata

Visible sites where crossing over occurred; points of attachment between homologous chromosomes during diplotene.

Recombinase

Enzyme that mediates the crossing-over process during genetic recombination.

Recombination nodules

Sites where crossing over occurs; enzyme-mediated recombination structures during prophase I.

Tetrad

Group of four chromatids formed by synapsis of two homologous chromosomes (each with two sister chromatids) in prophase I.

Homologous chromosomes

A pair of chromosomes with the same size, shape, and gene sequence, one from each parent.

Bivalent

A pair of homologous chromosomes held together during synapsis; another term for a tetrad.

Sister chromatids

Two identical copies of a replicated chromosome held together at the centromere.

Karyokinesis

Division of the nucleus (nuclear division) during cell division.

Interphase

Phase of the cell cycle when the cell grows and DNA is replicated before mitosis or meiosis.

Interkinesis

A short metabolic gap between meiosis I and meiosis II; no DNA replication occurs, centrioles duplicate, and meiosis II machinery is prepared.

Diploid

Cell or organism with two sets of chromosomes (2n).

Haploid

Cell or organism with one set of chromosomes (n); typically the gamete in sexual reproduction.

Gamete

Male or female reproductive cell that is haploid and fuses during fertilization.

Meiosis I

First meiotic division (reductional division) that halves the chromosome number by separating homologous chromosomes.

Reductional division

Meiosis I; division that reduces the chromosome number by half.

Equational division

Meiosis II; division that maintains the chromosome number; sister chromatids separate.

Independent assortment

Random orientation of homologous chromosome pairs at metaphase I leading to genetic variation in gametes.

Plant cytokinesis cell plate

In plants, cytokinesis occurs by the formation of a cell plate that develops into separating cell walls.

Animal cytokinesis furrow

In animals, cytokinesis occurs by a contractile actin filament ring forming a cleavage furrow that splits the cell.

Centrosome

Organizing center for the spindle apparatus; in animal cells it contains a pair of centrioles.

Centrioles

Cylindrical cell organelles within the centrosome that organize spindle formation.

Aster

Radial array of microtubules around each centrosome during early mitosis or meiosis.

Spindle fibers

Microtubules forming the spindle apparatus that separate chromosomes during cell division.

Chromatid

One of the two identical copies of a replicated chromosome, joined at the centromere.

Chromosome

DNA-protein complex carrying genetic information; consists of two sister chromatids during replication.