- The genetic material responsible for hereditary and variation is found in the nucleus
- The nucleus contains long- thread like structures called chromosomes which mainly consist of DNA and histones.
- Individual chromosomes are only visible when a cell is divided, when it isn't only a mass can be seen known as chromatin.
- Human body cells have 46 chromosomes in each nucleus and such a cell is described as diploid
- The egg and sperm cells only have one set of chromosomes which is the haploid number 23.
- The diploid number is the number of chromosomes in a zygote.
- In body cells the chromosomes can be arranged in pairs, the two members of each pair are identical so are described as homologous pairs.
- Every chromosome has a centromere
- Produces 2 identical daughter cells.
- The cell division of growth
- The bulk of the cell cycle is spent in interphase. The organelles replicate and the cell doubles in size.
1) Longest stage of division
2) The chromosomes become visible because the chromatin fibres shorten and thicken
3) Each chromosome consists of 2 chromatids
4) The centrioles move to opposite poles
5) The nucleolus disappears and the nuclear membrane breaks down
1) The chromosomes assemble at the equator of the spindle
2) They become attached to the spindle at their centromeres
1) The centromeres divide in two and the spindle fibres pull the daughter centromeres apart. The separated chromatids are pulled along behind.
2) The daughter chromosomes are now pulled to opposite poles.
1) The chromosomes reach the poles of the spindle
2) A nuclear membrane reforms around each of the two groups of chromosomes and the nucleoli disappear.
3) The spindle fibres disintegrate and centrioles replicate
4) A membrane is formed
- Mitosis is significant as it makes cells which are genetically identical. This is important in growth, repair and asexual reproduction. The chromosome number is maintained and there is no change in genetic material.
- During sexual reproduction, in the formation of the gametes, a reduction division called meiosis takes place
- The daughter cells have a haploid number of chromosomes.
- Meiosis is 2 divisions
- To find meiosis it is necessary to look inside anthers and ovules
- Meiosis is preceded an interphase stage during…