Meiosis
- Created by: Freja
- Created on: 10-04-21 13:11
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- Meiosis
- Meiosis 1
- Results in TWO HAPLOID CELLS
- Prophase 1- the chromosomes condense, the nuclear envelope disintegrates, the centrioles start moving to opposite poles, the spindle fibres begin to form. The homologues chromosomes pair up to form bivalents and crossing over occurs.
- Metaphase 1- chromosomes line up on the cell equator and the spindle fibres attach to the centromere. Independent assortment takes place.
- Anaphase 1- homologous chromosomes are pulled by the spindle fibres to the poles, The homologous chromosomes are pulled apart and one chromosome goes to each pole
- Telophase 1- The nuclear envelope reforms around each group of chromosome and the chromosomes uncoil.
- The cells undergo cytokinesis and those cells are now haploid cells.
- Meiosis 2
- Prophase 2 (Beginning of second division)- The chromosomes decondense, the nuclear envelope breaks down again and the spindle fibres reform.
- Metaphase 2- Chromo-somes are lined up on the equator by the spindle fibres and independent assortment occurs again, which causes more genetic variation.
- Anaphase 2- sister chromatids are split apart by the spindle fibres and the chromatids move to opposite poles of the cell.
- Telophase 2- Chromatids uncoil, the nuclear envelope reforms. The cell undergoes cytokinesis, so 4 haploid daughter cells are produced
- Results in 4 HAPLOID DAUGHTER CELLS
- Meiosis Produces Cells that are Genetically Different
- Crossing Over
- The chromatids entangle at the chiasmata (the point of breakage) and form recombinant chromosomes
- 1-Parent cells with homologous chromosomes after cross over and recombination
- 2-Homologous chromosomes are separated into different cells
- 3-Chromatids are separated by a further and all 4 cells produced have a different genetic composition
- 2-Homologous chromosomes are separated into different cells
- Independent Assortment
- The orientation of each homologous pair on the metaphase plate is random and independent of any other homologous pair.
- The maternal or paternal chromosome can end up facing either way.
- The 4 daughter cells have completely different combinations of the maternal and paternal chromosomes
- The orientation of each homologous pair on the metaphase plate is random and independent of any other homologous pair.
- Two gametes join together at fertilisation to form a zygote and the zygote then divides and develops into a new organism
- Crossing Over
- Haploid Cells
- Haploid- one copy of chromosomes (N) Diploid- two copies of chromosomes (2N)
- Meiosis is a reduction division, as the cells that divide by meiosis have the full number of chromosomes to start with, but the cells that are formed have half the number.
- Homologous Chromosomes
- Matching pair of chromo-somes, one inherited from each parent
- Chromo-somes are the same size and have the same genes, though they could have different versions of those genes (alleles)
- A human somatic cell contains 46 chromosomes (23 pairs of homologous chromo-somes)
- A type of cell division that happens in the reproductive organs to produce gametes
- Meiosis 1
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