meiosis
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What happens in meiosis?
• form of cell division that creates gametes that are haploid • produces 4 genetically unique cells • undergo 2 nuclear divisions
aim of meiosis 1
To separate homologous pairs of chromosomes into two cells
aim of meiotic division 2
to separate sister chromatids into 4 cells
what is a diploid cell
total number of chromosomes that are able to form homologous pairs, represented at 2n
what is a haploid cell
cell with chromosomes that cannot form homologous pairs, represented as n
prophase 1
Homologous chromosomes line up together in their pairs, forming a bivalent
When does crossing over occur and why does it create genetic variation?
occurs in prophase 1 - homologous chromosomes exchange material by crossing over sister chromatids which break and recombine, creating new combo of alleles
when does independent segregation occur and why does it create genetic variation?
occurs in metaphase 1 homologous chromosomes line up randomly on each side of the equator, opposite their homologue - new genetic combinations created
Anaphase 1
• spindle fibres contract • chromosome pairs are pulled apart by their centromeres
prophase 11
Two new spindles form at right angles to original spindle Chromatin condenses Nuclear envelope breaks down
why is meiosis important?
create cells with half number of chromosomes, increases genetic variation