This document shows an easy description of what occurs at each stage in meiosis, it was written for the pearsons Edecxel specification and covers everything you need to know.
Meiosis
Meiosis is a vital process which produces gametes to be used in sexual reproduction. Unlike mitosis, meiosis produces four
daughter cells all having genetic variation.
Meiosis
Interphase:
Before a cell divides interphase must take place, this includes
Cell growth
1. Increase in protein synthesis with the cell growing and amount of cytoplasm increasing.
2. The chromosomes are all copied. Chromatids copied (from 23 mum chromatids and 23 dad chromatids to 46 of both)
3. Cell prepares for division with the mitochondria splitting (in plants the chloroplast also divides.
Prophase 1:
The chromosomes begin to condense and become more visible like mitosis, but in meiosis they also pair up, they pair up with
their homologue partner (the same number chromosome from mom and dad, (chromosome 16 from mum and
chromosome 16 from dad)). This is so the same length and can match up at corresponding positions.
The main process which occurs in prophase 1 is ‘crossing over’
This process allows for genetic variations, as parts of each allele are shared.
Metaphase 1:
The chromosomes align in their pairs in the middle of the cell. Figure 1: Letters A, B and C represent genes
found on the chromosome. With the
This is different from mitosis where chromosomes align alone in the centre of the cell. lowercase and capital representing different
alleles.
Anaphase 1:
The pairs are pulled apart and moved to the opposite sides of the cell. When cells divide during meiosis, homologous
chromosomes are randomly distributed during
anaphase I, separating and segregating
Still in their homologous pairs. independently of each other. This is called
independent assortment. It results in gametes that
have unique combinations of chromosomes
Telophase 1:
Often two cells form at the end of telophase 1 as cytokinesis happens at the same time, this often produces two daughter
cells both having a pair of chromosomes in each (46 chromosomes but crossing over has occurred).
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