2. Genetic information is copied and passed onto daughter cells

role of mitosis

produces two genetically identical daughter cells for growth, repair, replacement and asexual reproduction of cells

3 stages of the cell cycle

interphase - G1, S, G2

mitosis

cytokenesis- cell division

what is mitosis?

a form of cell division that produces 2 genetically identical daughter cells, there are 4 stages: prophase, metaphase, anaphase and telophase

what happens in prophase?

Chromosomes condense and become visible

The nucleolus and the nuclear membrane break down.

Centrioles migrate to opposite poles

Spindle fibres form

what happens in metaphase?

centromeres attach to the spindle

chromosomes line up in middle/equator of cell

what happens in anaphase?

the centromeres divide into 2 and spindle fibres begin to shorten, this pulls sister chromatid towards opposite poles

what happens in telophase?

Chromatids reach the cell poles, becoming chromosomes again.

The spindle fibres breaks down, nucleolus and nuclear membranes reform

Chromosomes uncoil back to chromatin.

what happens in cytokenesis?

cell division

animal cells - cleavage furrow forms, cell membranes and cytoplasm indents from outside in
plant cells - cell plate forms and a new cell wall forms from the middle inwards

what happens in interphase?

G1- growth, organelle replication, organelle + protein synthesis

S- semi-conservative replication

G2- more growth and protein + ATP synthesis

what is mitosis controlled by and why?

controlled by genes to avoid tumours developing

how does meiosis produce genetic variation

• crossing over in prophase I

• independent assortment in metaphase I

• random fertilisation

what does meiosis produce?

4 genetically varied haploid cells to restore the diploid number of cells at fertilisation

differences in stages of meiosis I compared to mitosis

homologous chromosomes pair up in prophase (synapsis to form a bivalent)

crossing over occurs

pairs of chromes align and independent assortment occurs in metaphase

pairs of homologous chromosomes are separated in anaphase

chromosomes usually stay in condensed form in telophase

what is crossing over in prophase I?

Chromosomes twist around each other when pairing up, sections of chromatid may break off and rejoin with a corresponding chromatid at chiasmata (where they touch). This creates new combinations of alleles.

differences in stages of meiosis II compared to mitosis

new spindle forms at right angles to the old spindle in prophase
4 haploid gametes, each with a different genetic makeup are produced in cytokinesis

steps of mitosis practical (root tip squash)

grow roots, place roots in HCl to soften cell walls, rinse roots and stain by adding cut roots to a vial of acetic orcien, water bath for 5 mins, use forceps to transfer a few onto a slide, press down to squash root tip