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What is meiosis?
Haploid cells from a diploid cell
How many chromosomes do haploid cells have?
23
How many chromosomes do diploid cells have?
46
What does double haploid cells give?
Diploid cells
What is a homologous chromosome?
2 chromosomes that have the same set of genes
Where do the chromosomes come from in a homologous pair?
One from offsprings mother
One from offsprings father
What type of cells does mitosis form?
Diploid
What type of cells does meiosis form?
Haploid
What happens in interphase?
The cell grows and DNA replicates allowing to meiosis to start
What happens between meiosis 1 to meisosi 2?
What happens in Prophase 1?
Chromatin condenses into chromosomes
Nuclear envelope breaks down
Homologous chromosomes pair up (bivalence)
What happens in Metaphase 1?
All 23 homologous chromosomes line up in the middle of the cell
What happens in Anaphase 1?
Spindle fibres pull pairs apart
chromosome from each pair is at each end of the cell
What happens in Telophase 1?
Chromosomes decondense
Nuclear envelope re forms around the chromatin
What happens after Telophase 1?
Cytokines
What happens after Meiosis 1?
2 daughter cells have one chromosome from each of the parent cells pairs (23 in total)
What happens in Prophase 2?
Chromatid recondenses into 23 chromosomes made up
What happens in Metaphase 2?
Spindle fibres line the chromatids up in centre of cell
What happens in Anaphase 2?
Sister chromtids pulled apart
What happens in Telophase 2?
Nuclear envelope reforms around each group of 23 chromatids
Decondense to chromatin
What happens after telophase 2?
Cytokinesis leaving with 4 daughter cells
What are the differences between mitosis and meiosis?
Mitosis 1 division but Meiosis 2
Mitosis- 2 identical diploid cells Meiosis- 4 haploid cells genetically different
Mitosis- Growth and Tissue Repair Meiosis- To produce gametes for sexual reproduction
How does meiosis create genetic variation?
Crossing over
Independent assortment
Mutation
Where does crossing over?
Prophase 1 in Meiosis 1
What do chromatids do in crossing over?
Homologous chromosomes are closer enough so chromatids twist and exchange with partner
Does crossing over always result in genetic variation?
No
What does crossing over, mutations and random assortment all create?
New combinations of alleles in the daughter cells
When does independent assortment occur?
Metaphase 1
What do the homologus chromosomes do in independent assortment?
alleles Pair up at random
How do mutations create variation?
Can have non- disjunction which can cause gametes to not have correct number of chromsomes
