what are the stages of the cell cycle?
- G1, S, G2 (interphase)
- prophase, metaphase, anaphase, telophase (mitosis)
what is the importance of mitosis?
- growth
- repair of tissue
- asexual reproduction
in what form is DNA made into for cell division?
- DNA coiled into chromosomes (either one or two sister chromatids that are exact copies of each other thanks to semi-conservative replication)
what is occurring during the G1 phase?
- cell functions normally, growing and synthesising more organelles
what happens during the S phase?
- DNA replication (DNA quantity doubles)
what happens during the G2 phase?
- proteins that are needed for cell division are synthesised
what are the differences between cells that have undergone mitosis and ones that have undergone meiosis?
- mitosis: diploid, complete set of chromosomes, genetically identical, in somatic cells
- meiosis: haploid, half no. of chromosomes, genetically different (due to crossing over and independent assortment)
what happens during prophase (mitosis)?
- DNA condensed into chromosomes
- nuclear envelope disintegrates and nucleolus disappears
- centrioles move to poles
- spindle fibers form
what happens in metaphase (mitosis)?
- chromosomes line up on the equator
- spindle fibres attach to centromeres
what happens in anaphase (mitosis)?
- spindle fibres contract, pulling sister chromatids apart towards poles
- centromeres split
- sister chromatids become daughter chromosomes
what happens in telophase (mitosis)?
- chromosomes unravel into chromatin
- nuclear membrane reforms
- spindle fibres disintegrate
- cytokinesis (animal cells: cytoplasm pinches in, plants: cell plate forms)
what happens during prophase I (meiosis)?
- DNA breaks and reforms
- homologous chromosomes pair up (one from mother, one from father) to form a bivalent
- crossing over occurs at same point on each chromatid on each chromosome (point is called chiasmata)
what are homologous chromosomes?
chromosomes with the same genes on but different alleles (different forms of same gene)
what happens in metaphase I?
- bivalents line up on either side of equator in an independent assortment
- fibres attach by centromere
what happens in prophase II that is different from prophase?
- no crossing over (as no bivalents)
- new spindle fibres form perpendicular to previous spindle fibres
what is difference between anaphase II/ anaphase (mitosis) and anaphase I?
- II/mitosis: sister chromatids pulled apart
- I: paired chromosomes in bivalent are pulled apart
