Meiosis and genetic variation

Process of meiosis:

Every diploid cell of an organism has two complete sets of chromosomes: one set provided by each parent. During meiosis homolgous pairs of chromosomes separate so that only one chromosome from each pair enters a daughter cell. This is known as the haploid number.

First division (meiosis 1) -

• Homologous chromosomes pair up and their chromatids wrap around each other
• Equivalent proportions of these chromatids may be exchanged in a process called crossing over
• By the end of this division the homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells

Interphase -

• DNA unravels and replicates
• Producing a double chromatid which forms chromosomes

Prophase 1 -

• Chromosomes arrange into homolgous pairs
• Centrioles move to oposite ends of the cell
• Spindle fibres begin to form
• Nuclear envelope breaks down

Metphase 1 -

• Homologous pairs line up across the centre of the cell
• Spindle fibres attach to the centromeres of the chromosome

Anaphase 1 -

• Spindle fibres begin to contract
• Homologous pairs separate and go to each end of the cell

Telophase 1 -

• Nuclear envelope forms around each group of chromosomes
• Cytokinesis occurs

Second mitotic division (meiosis 2) -

• The chromatids move apart
• At the end, four cells have…