| What is meiosis | It is a type of cell division that happens in the reproductive organs to produce gametes |
| Define gametes | Haploid sex cells produced by meiosis in organisms that reproduce sexually (sperm and eggs) |
| Define somatic cell | Any cell of a living organism but reproductive cells |
| Define zygote | The diploid cell produced by fertilisation (fertilised eggs) |
| What is a homologous chromosome | Pairs of matching chromosomes |
| Difference between haploid and diploid cells | Haploid = half the normal chromosomes number
Diploid = normal number of chromosomes |
| What is the importance od meiosis | Produces genetic variation during sexual reproduction by independent assortment and crossing over. |
| What are the main stages of meisos | Interphase, prophase 1, metaphase 1, anaphase 1, telophase 1, prophase II, metaphase II, anaphase II, telophase II |
| Describe interphase | - Cell's DNA unravels and replicates to produce double armed chromosomes called sister chromatids |
| Describe prophase 1 | - Chromosomes condense
- homologous chromosomes pair up and crossing over occurs
- centrioles move to opposite poles of the cell forming spindle
- nuclear envelope breaks down |
| Describe metaphase 1 | - homologous pairs line up across the equator of the cell and attach to the spindle by their centromeres |
| Describe anaphase 1 | - spindles contract, pulling pairs apart |
| Describe telophase 1 | - a nuclear envelope forms around each group of chromosomes
- cytokinesis occurs and 2 haploid daughter cells are produced |
| Describe prophase II | - chromosomes condense
- nuclear envelop breaks and spindle forms |
| Describe metaphase II | - chromosomes line up at the equator
- independent assortment occurs |
| Describe anaphase II | - sister chromatids are separated randomly |
| Describe telophase II | - chromatids assemble at poles
- cytokinesis occurs
- 4 daughter haploid cells are produced |
| Define bivalent | homologous chromatids referred to after crossing over |
| Explain crossing over | - occurs during prophase 1
- homologous pairs of chromosomes come together and pair up
- the chromatids twist around each other and bits of the chromatids swap over |
| How does crossing over create variation | The chromatids still contain the same genes but now have different combinations of alleles |
| Explain independent assortment | - Of chromosomes happen during metaphase 1
- Of chromatids happen during metaphase II
- homologous pairs line up and are separated. It's completely random which chromosome or chromatid from each pair end up in the daughter cells |
| How does independent assortment create variation | The 4 daughter cells produced have completely different combinations of those maternal and paternal chromosomes. |
