Cell Division

Define mitosis

Produces duplicate copy of original somatic cell (diploid cell - 46 chromosomes)

Define meiosis

Produces gamete cells (sex cells in ovaries and testes) with half the amount of chromosomes (haploid cell - 23 chromosomes)

State two main phases of cell cycle

Mitosis (cell division) and interphase (cell grows and performs normal functions)

Name stages of mitosis

Prophase, metaphase, anaphase and telophase

Describe prophase

Early prophase - chromatin fibres condense into chromosomes (each chromosome is a pair of identical chromatids joined by centromere)

Later prophase - kinetochore forms spindle fibres at each pole of cell, nucleolus disappears and nuclear envelop breaks down

Describe metaphase

Spindle fibres align chromatid pairs in equator of cell (midpoint region called metaphase plate)

Describe anaphase

Centromeres split to separate chromatid pairs towards opposite poles of cell

Chromatids become chromosomes (appear V shaped when taken towards poles)

Describe telophase

Once at opposite poles, chromosomes uncoil to form chromatin

Nuclear envelop forms around chromatin mass and spindle fibres break up

Describe cytokinesis

Begins in late anaphase - formation of cleavage furrow (appears midway between centrosomes and extends around periphery of cell)

Actin microfilaments form contractile ring (splits cell membrane)

Describe prophase I

Chromosomes condense, nuclear envelop and nucleolus disappear, spindle fibres form.

The two sister chromatids of each pair of homologous chromosomes pair off (synapsis) and exchange genetically different parts of non-sister chromatids (crossing-over) - exchange of genes for new combinations

Describe metaphase I

Chromosome pairs line up along metaphase plate of cell

Describe anaphase I

Pair of chromosome separated by spindle fibres to opposite poles of cell (paired chromatids remain together whereas during mitotic anaphase, chromatids separate)

Describe telophase I and cytokinesis

Same as mitotic telophase and cytokinesis - produces two diploid cells

Describe prophase II, metaphase II, anaphase II and telophase II

Same as mitotic prophase, metaphase, anaphase and telophase.

Results with four haploid cells