Stages and Significance of Meiosis and Mitosis

A comprehensive vocabulary flashcard set covering the definitions, stages, substages, structures, and significance of mitosis and meiosis based on the lecture notes.

Mitosis

Nuclear division process by which the nucleus divides to produce two new nuclei, resulting in two daughter cells that are genetically identical to each other and to the parental cell.

Cytokinesis

The division of the cytoplasm, which together with mitosis lasts for around one to two hours.

Prophase (Mitosis)

The preparatory stage of mitosis during which centrioles move toward opposite sides of the nucleus, chromosomes condense into visible threads, nucleoli fade, and the nuclear envelope fades.

Metaphase (Mitosis)

The stage of mitosis where chromosomes become arranged so their centromeres align in one place halfway between spindle poles, with long axes at $90$ degrees to the spindle axis.

Metaphase Plate

The plane of alignment halfway between the spindle poles where chromosomes or tetrads line up during cell division.

Anaphase (Mitosis)

The stage of mitosis initiated by the separation of sister chromatids at their centromere junction point, after which daughter chromosomes move toward opposite poles.

Telophase (Mitosis)

The stage of mitosis when daughter chromosomes reach opposite poles, uncoil, spindle fibers disappear, new nuclear membranes form around each set, and nucleoli reform.

Meiosis

The cell division process involving two successive divisions of a diploid nucleus that reduces genetic information to produce haploid gametes or spores.

Haploid Cell

A cell containing one set of chromosomes ($N$) and half the DNA of diploids, found in gametes such as sperm and eggs.

Diploid Cell

A cell containing two sets of chromosomes ($2N$), found in most body cells, supporting the sexual reproduction cycle.

First Meiotic Division

The reduction division of meiosis that reduces the number of chromosomes, subdivided into leptonema, zygonema, pachynema, diplonema, and diakinesis.

Leptonema

The first substage of Prophase I where replicated chromosomes have coiled and are already visible, maintaining the same chromosome number as the diploid cell.

Zygonema

The substage of Prophase I where homologous chromosomes begin to pair and twist around each other in synapsis to form a bivalent tetrad.

Synapsis

The specific pairing and twisting of homologous chromosomes around each other during zygonema.

Bivalent Tetrad

The structure formed during synapsis in zygonema that consists of four chromatids.

Pachynema

The substage of Prophase I where chromosomes become much shorter and thicker and undergo crossing-over.

Crossing-over

The process of physical exchange of chromosome regions between homologues during pachynema, resulting in genetic recombination.

Diplonema

The substage of Prophase I where sister chromatids begin to separate, revealing the chiasma.

Chiasma

The area of contact between two non-sister chromatids visible during diplonema.

Diakinesis

The final substage of Prophase I where tetrad chromatids condense further and chiasma terminalize down to the ends.

Metaphase I

The meiotic stage where synapsed tetrads align at the metaphase plate and spindle microtubules attach to centromere regions of homologues.

Anaphase I

The meiotic stage where homologous chromosomes separate; in humans, cells contain $23$ double-stranded chromosomes consisting of two sister chromatids joined at centromeres.

Telophase I

The meiotic stage where dyads complete migration to poles, nuclear membranes form, and cytokinesis yields two haploid daughter cells.

Prophase II

The initial stage of the second meiotic division where dyads contract.

Metaphase II

The stage of the second meiotic division where centromeres are directed to the equatorial plate and divide.

Anaphase II

The stage of the second meiotic division where sister chromatids (monads) move away from each other toward opposite spindle poles.

Telophase II

The final stage of the second meiotic division where monads form two groups at the poles, nuclear membranes reform, chromosomes uncoil, and cytokinesis follows.

Cleavage Furrow

The pinching structure formed during cytokinesis in animal cells that splits the cell into two.

Cell Plate

The structure formed between nuclei during cytokinesis in plant cells that develops into a new cell wall.

Independent Assortment

The random alignment of chromosome pairs during Metaphase I before separation, ensuring each reproductive cell receives a unique mix of chromosomes.