Cytogenetics, Cell Cycle & Polyploidy

Mitosis

A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus.

Prophase

The first stage of mitosis where chromosomes condense and the mitotic spindle forms.

Metaphase

The stage where chromosomes align along the metaphase plate (center of the cell).

Anaphase

The stage where sister chromatids separate and move toward opposite poles.

Telophase

The final stage where new nuclear membranes form around the two sets of separated chromosomes.

Meiosis (Meiosis I & II)

A type of cell division that reduces the chromosome number by half, producing four genetically unique haploid gametes or spores.

G1 Phase

Gap 1 phase of the cell cycle where the cell grows and performs normal metabolic roles prior to DNA replication.

G2 Phase

Gap 2 phase where the cell grows further and prepares proteins necessary for mitosis.

Synapsis

The close pairing of homologous chromosomes alongside each other during prophase I of meiosis.

Chiasma (pl. Chiasmata)

The X-shaped point where homologous chromosomes remain in contact during prophase I, representing sites where crossing over (recombination) has occurred.

Crossing Over / Recombination

The exchange of genetic material between non-sister homologous chromatids during meiosis I, creating new allele combinations.

Homologous Chromosomes

A pair of chromosomes (one from each parent) that have the same length, gene sequence, and centromere position.

Nondisjunction

An error during cell division in which homologous chromosomes or sister chromatids fail to separate properly, migrating to the same pole.

Aneuploidy

A chromosomal variation characterized by the addition or deletion of fewer than a full set of chromosomes (e.g., trisomy $2n+1$, monosomy $2n-1$).

Euploidy

Having complete sets of chromosomes (multiples of the base chromosome number $n$).

Base Chromosome Number ($n$ or $x$)

The number of chromosomes in a single complete basic set comprising a species' genome.

Ploidy / Sets

The number of complete sets of chromosomes in a cell.

Diploid ($2n$)

Having two complete sets of chromosomes.

Polyploid / Polyploidy

The state of having more than two complete sets of chromosomes.

Autopolyploid / Autopolyploidy

A polyploid condition formed by the doubling or union of multiple chromosome sets originating from the same single species.

Allopolyploid / Allopolyploidy

A polyploid condition formed by the hybridization and subsequent chromosome doubling of two or more distinct species.

Colchicine

A chemical compound used experimentally to disrupt microtubule formation, preventing cell division and leading to chromosome doubling (polyploidization)