Anaphase: The stage of mitosis in which chromatids separate and are pulled towards opposite poles of the cell by the spindle.

Anaphase I: Stage of meiosis when homologous chromosomes are separated, with spindle fibres pulling one member of the air to one pole and the other chromosomes to the opposite pole.

Anaphase II: Stage of meiosis when centromeres split, sister chromatids separate and are pulled to opposite poles by shortening spindle fibres.

Apoptosis: Programmed cell death.

Cell cycle: The series of events that take place in a cell leading to its division to produce two daughter cells.

Centriole: Two cylinders composed of microtubules which are involved in the process of mitosis and cell division in some eukaryotic cells.

Centromere: The region of a chromosome that joins two sister chromatids and attaches to microtubule spindle fibres during mitosis.

Chiasmata: The points at which crossing over occurs between homologous chromosomes.

Chromatid: One half of a replicated chromosome.

Chromosomal mutation: A visible change in the number or structure of chromosomes in a cell.

Chromosome: A linear DNA molecule which during prophase, condenses and becomes visible as two chromatids joined at the centromere.

Crossing over: The process in which homologous chromosomes exchange alleles during prophase I of meiosis.

Cytokinesis: The division of a cell to form two new cells.

Differentiation: The development of unspecialised cells to form specialised cells.

Diploids: Cells that have two sets of chromosomes.

Gamete: A haploid reproductive cell that fuses with another gamete during fertilisation.

Haploids: Cells that have one set of chromosomes.

Homologous chromosomes: A pair of chromosomes, one maternal and one paternal, that are the same length and carry the same gene loci but may have different alleles.

Independent assortment: The random assortment of chromosomes during metaphase I of meiosis and of chromatids during metaphase II of meiosis determines segregation in anaphase I/II.

Interphase: The phase of the cell cycle in which new DNA and organelles are synthesised.

Metaphase: The phase of mitosis in which chromosomes line up at the equator of the cell.

Metaphase I: Stage of meiosis when bivalents line up at the cell equator.

Metaphase II: Stage of meiosis when chromosomes randomly line up at the cell equator.

Meiosis: A form of nuclear division that halves chromosomes number and introduces genetic variation; occurs to produce gametes.

Mitosis: A form of nuclear division in which two genetically identical nuclei are formed; occurs in somatic cells.

Multipotent: Cells able to differentiate into a limited range of different cell types.

Non-disjunction: A type of chromosomal mutation when homologous pairs or pairs of chromatids fail to separate and move to opposite poles, so daughter cells have extra or too few chromosomes.

Pluripotent: Cells able to differentiate into any type of cell but cannot form a whole organism. Found in late embryos at the 50-100 cell stage.

Prophase: The stage of mitosis in which chromosomes condense and become visible and the spindles form.

Prophase I: Stage of meiosis when homologous chromosomes pair up to form a bivalent and swap equivalent sections of DNA at chiasma.

Prophase II: Stage of meiosis when the nuclear envelope disappears, chromosomes condense and spindle fibres begin to form.

Spindle: Microtubule fibres that attach to centromeres and separate sister chromatids during eukaryotic mitosis.

Stem cells: Undifferentiated cells that can divide and differentiate into a range of different cell types.

Telophase: The stage of mitosis in which two new nuclear envelopes form around the two sets of daughter chromosomes formed in nuclear division.

Telophase I: Stage of meiosis when animal cells, form nuclear envelopes around each haploid set of chromosomes.

Telophase II: Stage of meiosis when the nuclear envelope form around the 4 haploid sets of daughter chromosomes.

Totipotent: Cells able to differentiate into any type of cell and can divide to form a whole organism. Found in very early embryos.

Zygote: A diploid cell formed when two haploid gametes fuse at fertilisation.