Keywords

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.