1.6: The cell cycle and division

Histone

Protein that DNA is wound around.

Chromosomes

Made up of histones and DNA, only visible prior to cell division.

Sister chromatids

Two copies of an exact chromatid, which lie parallel and are joined in the middle.

Centromere

Join sister chromatids together.

Ploidy level

Number of complete sets of chromosomes in an organism.

Haploid number

Number of chromosomes in a complete set.

Diploid

Two sets of homologous chromosomes.

Polyploid

Organisms with more than two complete sets of chromosomes.

n

Symbol for haploid number.

Interphase

Phase of the cell cycle where growth and synthesis occur.

Mitosis

Type of cell division where two genetically identical daughter nuclei are produced.

Cytokinesis

Division of the cytoplasm to produce two genetically identical daughter cells.

Prophase

Longest of the four stages of the cell cycle stages, where chromosomes condense and spindle fibres are produced.

Protein microtubules

Formed by the centrioles to produce spindle fibres.

Spindle fibres

Extend from pole to pole, and pull chromatids apart.

Metaphase

Relatively short stage where the centromeres of the chromatids attach to the spindle fibres in a line.

Anaphase

Stage of the cell cycle where the centromeres divide and are pulled to the poles centromere first.

Telophase

Final stage of the cell cycle, when the nuclear envelope reforms around the chromosomes.

Meiosis

Type of cell division four genetically diverse daughter cells are produced.

Bivalents

Pairs of homologous chromosomes, with one maternal and one paternal, formed through synapsis.

Synapsis

Process of forming bivalents.

Chiasma

Place where equivalent segments of DNA are exchanged.

Crossing over

Term for equivalent segments of DNA exchanging across a chiasma, happens during prophase 1.

Independent assortment

Bivalents lining up at the equator randomly, therefore a randomised combination of maternal and paternal chromosomes going into each daughter cell. Occurs during metaphase 1 and 2.

Cleavage furrow

How cytokinesis occurs in animals, formed when the mother cell pinches inwards.

Cell plate

How cytokinesis happens in plants, formed when carbohydrate containing vesicles collect on the equator and extend outwards, forming a lamella.

Mitopic index

Percentage of cells currently going through mitosis.

Chromatin

Made from DNA and is wrapped around histones to make a chromosome.

Nucleosome

A single histone wrapped with chromatin, many of these make a chromosome.

Homologous pairs

One chromosome is from the mother and one from the father, also known as matching pairs. Occurs in diploid species.

Middle lamalla

Occurs in plant cells. When the cell plate extends across the cell due to cellulose building up on each side.

Tumour suppressor genes

Genes that prevent rapid replication, which can cause tumours.

Proto-oncogenes

Tumour supressor genes before alteration that makes them cause cancer