meiosis and mitosis

Mitosis and Meiosis in Biology AQA

MITOSIS

Mitosis process

1. chromosome replication- chromosomes replicate forming x shaped structure (of 2 cromatids)

2. Alignment - chromosomes align in middle of cell

3. Separation - Chromatids are pulled apart to opposite ends of cell

4. new nucleus formation - new nucleus formed around each chromatid

5. cytokinesis - cytoplasm and cell membrane divide resulting in 2 genetically identical daughter cells

mitosis in humans info

1. chromosomes are duplicated to 46 (92 chromatids total)

2. sub cellular increase, more ribosomes and mitochondria to support division

3. chromatid separation- pulled apart (46 chromatids per new cell)

4. cytokinesis - 2 genetically identical daughter cells

reasons for mitosis

• essential for repair

• growth & development: needed to increase cell no.

• human reproduction: after fertilisation, zygote divided by mitosis to develop an embryo

MEIOSIS

meiosis is cell division that occurs is sex organs to produce haploid gametes

meiosis is needed to ensure chromosomes are halved form diploid to haploid to maintain chromosome number post fertilisation

meiosis process

1. each chromosome replicates

2. align in the middle, to be pulled apart and separated to opposite ends of tables

3. sister chromatids line in centre again and pulled apart

4. this produces 4 genetically distinct haploid daughter cells

key points

• meiosis produced 4 haploid cells from a diploid parent

• gametes = haploid. this prevents doubling of chromosomes at fertilisation so maintains right number of chromosomes in zygote.

importance of meiosis

• results in genetic variation: increases genetic diversity by shuffling maternal and paternal chromosomes

• produces gametes