For cells to divide the genetic code needs to be copied for each daughter cell
Genetic code in eukaryotes is arranged onto sturctures called chromosomes
Before the cells divide the chromosomes are replicated
X shaped chromosomes which become visible after
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Homologous Pairs
Chromosomes come in homologous pairs
One of each pair comes from each parent
Total number of chromosomes is the diploid number
Gametes only contain single chromosomes meaning they are haploid
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Mitosis
Cell division used to produce exact replicas of the parent cell
Used to produce the cells required for growth and repair of organisms
Used in asexual reproduciton when large numbers of identical offspring are produced rapidly
In tumours mitosis can be con
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Interphase
Longest stage of cell cycle
The cell grows and produces new organelles
DNA replication takes place
The chromosomes are not yet visible
Very active time for the cell and most activities require ATP
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Prophase
Chromosomes super-coil to become visible
Can be seen to consist of 2 chromatida joined by the centromere
Animals and simple plants - the centrioles divide and migrate to opposite poles of the cell
Centrioles produce spindles which extend from pole to pole
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Metaphase
Chromosomes arrange themselves on the equator
Attach to the spindles
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Anaphase
The spindle fibres contract
Pull the separated chromatids to opposite poles, centrosome first
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Telophase
When the chromatids reach the poles they are referred to as chromosomes again
DNA lengthens as it uncoils and chromosomes are no longer visible
Spindles break down and the centrioles replicate
Nucleoli reappear and the nuclear membranes reform
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Cytokinesis
Occurs as the daughter cells divide
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Meiosis
The cell division that produces haploid gametes from diploid cells
Sexual reproduction meiosis introduces the variation necessary for the long term survival of species in a changing environment
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Meiosis Variation One
Halving of the chromosome number produces gametes which are haploid
Allow the genotypes of both parents to be mixed at fertilisation
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Meiosis Variation Two
Pairs of homologous chromosomes arrange themselves independently on the spindle during metaphase 1
Separate as they show independent assortment
The daughter cells produced contain different mixtures of maternal and paternal chromosomes
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Meiosis Variation Three
Crossing over during prophase 1 of meiosis exchanges material between the maternal and paternal chromosomes
Breaks up genes that may have been 'linked' together and creates new combinations of linked genes
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Interphase - Meiosis
The cell is replicating its DNA
Forms new organelles
Chromosomes are not visible
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Prophase 1
Chromosomes super coil becoming shorter and fatter
Seen to consist of 2 chromatids
Centrioles migrate to opposite poles
Produce microtubules that form the asters which form the spindles
Higher plants do not produce centrioles
Chromosomes associate in thei
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Metaphas 1
The homologous pairs of chromosomes alighn on the equator of the spindles
Maternal and paternal chromosomes associate randomly either side of the spindles
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Anaphase 1
Chromosomes in each bivalent are pulled to opposite poles
Random arrangement during metaphase each pole contains a mixture of maternal and paternal chromosomes
Nuclear membrane reforms around each nucleus of haploid chromosomes
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Telophase 1
2 haploid daughter cells are produced by cytokinesis
Chromosomes remain in their condensed form
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Prophase 11
New spindles form perpendicular to those in prophase 1
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Metophase 11
Chromosomes line up on the equator
Each chromosome is attached to the spindle by its centromere
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Anaphase 11
Centromeres divide as the chromatids are pulled to opposite poles
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Telophase 11
The chromosomes decondense
No longer visible
Spindle disappears
Nuclear membranes reform and cytokinesis occurs
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Meiosis Production
4 haploid daughter cells produced by meiosis
Each genetically different
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Other cards in this set
Card 2
Front
Homologous Pairs
Back
Chromosomes come in homologous pairs
One of each pair comes from each parent
Total number of chromosomes is the diploid number
Gametes only contain single chromosomes meaning they are haploid
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