The cell cycle


longest phase- splits into G1, S, G2cell size increasesincreases energy storesreplicates organelle DNA copied

M phase (mitotic)

mitosis and cytokinesis

G1 phase

organelles are replicated - requires lots of proteins transcription/translation occurscell size increases

S phase

DNA synthesis chromosomes replicated

G2 phase

energy stores used during s phase replaced damaged chromosomes repaired size of cell increases transcription/translation occurs


division of nucleuschromosomes separated into 2 nucleicytokinesis: cell divides into 2 used for asexual reproduction (eg. in aphids)

G0 phase

cells exit cycle1. full differentiated cells2.DNA is damaged, cells permanently stay : senescent cells3. B memory cells temporarily enter can be triggered to re enter

G1 checkpoint

checks for DNA damagechecks cell size before s phase

G2 checkpoint

end of G2 checks cell size checks DNA damage

metaphase checkpoint

makes sure chromosomes are correctly attached to spindle fibres.

Diploid cell

2 sets of chromosomes (pair)most human cells are diploid cells

During interphase

the chromatin is spread out and not condensed into chromosomes ( loose open structure ) DNA accessible for transcription/ translation.

chromosomes replicated

into sister chromatids- join at centromereduring interphase- not visible as structures yetchromosomes: single long strand of DNA

stages of mitosis

prophase, metaphase, anaphase, telophase


chromosomes condense + become visiblenucleolus disappears,nuclear membrane breaks down,pair of centrioles move to each pole of cell,protein form spindle fibres that attach to centromeres,spindle fibres move chromosomes to cell centre


chromosomes line up at equator


centromeres divide, spindle fibres shorten, sister chromatids pulled to each pole of cell


spindle fibres disappear, nuclear membrane reforms, chromosomes uncoil back to chromatin state, nucleolus reappears,


cytoskeleton pulls cell membrane inward, division of the cytoplasm to form two separate daughter cells

differences in plant cells

no spindle fibres, no centrioles, vesicles from Golgi apparatus form membrane structures during cytokinesisnew cellulose cell wall forms


produces genetically different gametes eg. sperm, eggs, pollenonly takes place in sex organs haploid cells- individual chromosomefertilisation- gametes fuse to form zygote (diploid)starts with diploid cell, produces 4 haploids

homologous chromosomes

one from each parent, have identical genes, different alleles ( that can be inherited), crossing over- 2 chromatids of 2 chromosomes wrap around each other ( forms bivalent )chiasma- point where they are joined parts of chromatid breaks off exchange between chromosomes, they can now exchange alleles as they've exchanged DNA

stages of meiosis

prophase 1, metaphase 1, anaphase 1, telophase 1, cytokinesis, prophase 2, metaphase 2, anaphase 2, telophase 2, cytokinesis

prophase 1

chromosomes condense + visible, homologous chromosomes form chiasmata, crossing over- alleles exchange between homologous chromosomes, nuclear membrane breaks down,centrioles move to opp poles,spindle fibres form spindle apparatus

metaphase 1

homologous pairs line up at equator

anaphase 1

spindle fibres shorten, homologous pairs move to opposite poles,chiasmata breaks

telophase 1

nuclear membrane reforms,chromosomes uncoil back to chromatin state, cytokinesis- 2 cells form (haploid)

prophase 2

chromosomes condense, nuclear membrane breaks down, spindle fibres form

metaphase 2

chromosomes line up at equator/ spindle

anaphase 2

centromeres divide, spindle fibres shorten, chromatids pulled to each pole

telophase 2

nuclear membrane reforms, chromosomes uncoil back to chromatin state, cytokinesis- 2 haploid cells produced

independent assortment

cant predict weather paternal or maternal chromosome will end up in which gamete