Mitosis and Meiosis

Cell cycle

Stages through which a cell passes from one cell division to the next

Checkpoint

A key transition point at which progression to the next stage in the cell cycle is regulated

Interphase

Major phase of the cell cycle between cell divisions. The cell grows, develops, and functions.

M (Mitotic) Phase

The major phase of the cell cycle that encompasses active cell divisions; Includes mitosis (nuclear divisions) and cytokinesis (cytoplasmic divisions)

Centrosome

Structure from which the spindle apparatus develops; it contains the centriole.

Prophase

Stage of mitosis in which the chromosomes contract and become visible, the cytoskeleton breaks down, and the mitotic spindle begins to form

Prometaphase

Stage of mitosis in which the nuclear membrane breaks down and the spindle microtubules attach to the chromosomes.

Metaphase

Stage of mitosis in which chromosomes align in the center of the cell

Anaphase

Stage of mitosis in which sister chromatids separate and move toward opposite spindle poles

Telophase

Stage of mitosis in which the chromosomes arrive at the spindle poles, the nuclear membrane reforms, and the chromosomes relax and lengthen.

Cytokinesis

Process by which the cytoplasm of cell divides

Meiosis

For gametes - eggs and sperm. Process by which the chromosome of a eukaryotic cell divide to give rise to haploid reproductive cells. Consists of two divisions: meiosis I and meiosis II.

Meiosis I

First stage of meiosis. In meiosis I, chromosomes number is reduced by half

Prophase I

Stage of meiosis I in which chromosomes condense and pair, crossing-over takes place, the nuclear membrane breaks down, and the mitotic spindle forms

Leptotene

First substage of prophase I in meiosis. In leptotene, chromosomes contact and become visible

Zygotene

Second substage of prophase I in meiosis. In zygotene, chromosomes enter into synapsis

Pachytene

Third stage of prophase I in meiosis. The synaptonemal complex forms during pachytene.

Diplotene

Fourth substage of prophase in meiosis I. In diplotene, centromeres of homologous chromosomes move apart, but the homologs remain attached at chiasmata

Diakinesis

Fifth substage of prophase I in meiosis. In diakinesis, chromosomes contract, the nuclear membrane breaks down, and the spindle forms.

Synapsis

Close pairing of homologous chromosomes

Crossing Over

Exchange of genetic material between homologous but non-sister chromatids.

Metaphase I

Stage of meiosis I in which homologous pairs of chromosomes align in the center of the cell along the metaphase plate.

Metaphase Plate

Plane in the cell between two spindle poles. In metaphase, chromosomes align on the metaphase plate.

Anaphase I

Stage of meiosis I in which homologous chromosomes separate and move toward the spindle poles

Telophase I

Stage of meiosis I in which chromosomes arrive at the spindle poles

Interkinesis

Period between meiosis I and II

Meiosis II

Second phase of meiosis. Events in meiosis II are similar to those in mitosis

Prophase II

Stage of meiosis in which events of interkinesis are reversed; chromosomes condense, the spindle reforms, and the nuclear membrane breaks down. Some cells skip this stage.

Metaphase II

Stage of meiosis II in which the individual chromosomes align in the center of the cell

Anaphase II

Stage of meiosis II in which sister chromatids separate and the chromatids are pulled to opposite poles.

Telophase II

Stage of meiosis II in which chromosomes arrive at the spindle poles

Recombination

A process that produces new combinations of alleles. Offspring inherit a combination of alleles that differs from that of either parent.