Mitosis and Meiosis

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What does mitosis produce?
Cells that are genetically identical to the parent cell
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What does meiosis produce?
Cells that are genetically different to the parent cell
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How many chromosomes do the daughter cells of mitosis have?
The same number that the parent has
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How many chromosomes do the daughter cells of meiosis have?
Half the number that the parent has
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Why do cells divide by mitosis?
To repair damaged cells, replace old cells and for growth
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Why do cells divide by meiosis?
To create gametes
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Where is a good place to see mitosis taking place?
A root tip as it is a meristematic region
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Where could you view meiosis?
Testes, ovaries and anthers
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What is the diploid number in humans?
46 (23 pairs)
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What is the haploid number in humans?
23
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Name all the stages involved in mitosis
Interphase, Prophase, Metaphase, Anaphase, Telophase
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What other process happens after telophase and what happens?
Cytokinesis, it's the division of the cytoplasm into equal portions.
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How does cytokinesis happen?
This occurs as the plasma membrane in the middle of the cell is drawn inwards to form a cleavage furrow
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What are the 3 stages in interphase?
G1, S, G2
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What happens in G1?
This is where cell components are synthesised
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What happens in S?
This is where cell components and DNA are replicated
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What happens in G2?
This is where growth continues until mitosis occurs
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How does cancer occur?
When cells divide uncontrollably
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What stage does a cell spend the majority of it's life in?
Interphase
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When do chromosomes become visible?
During prophase
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What does a chromosome consist of?
Sister chromatids joined at a point called the centromere.
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What are homologous chromosomes?
They are two chromosomes that determine the same characteristic
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What happens during interphase?
New organelles are made, ATP is synthesised, Proteins are synthesised, DNA is replicated
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What happens during early prophase?
Chromosomes become shorter and thicker (they're now visible)
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What happens during late prophase?
Centrioles move to opposite poles of the cell, Spindle apparatus begins to form, The nuclear envelope disintegrates, the nucleolus dissapears
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What happens during metaphase?
Chromosomes align along the equator, the spindle fibres attach themselves to the centromeres
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What happens during anaphase?
The spindle fibres contract, the centromeres split and one chromatid from each pair is pulled towards opposite poles of the cell
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What happens during telophase?
The spindle apparatus breaks down, the nuclear envelope reforms are the two sets of chromosomes, the nucleolus reforms, centrioles replicate and the chromosomes become longer and thinner
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Where does mitosis occur in humans?
Epithelial cells and bone marrow
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What happens during early prophase I?
Chromosomes shorten and thicken and become visible under a light microscope, the chromosomes associate into their homologous pairs
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What is the process called by which homologous chromosomes pair up and what are they called after?
Synapsis, bivalent
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What happens during late prophase I?
The 4 chromosomes wrap around each other, chiasmata form, the nuclear membrane break down, the nucleolus disappears, the centrioles move to the opposite poles of the cell
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What are chiasmata?
These are points where the chromosomes have entwined
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What is crossing over?
The swapping of portions of chromatids i.e. the exchange of genetic material is termed crossing over
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What happens during metaphase I?
Bivalents line up on the equator, the spindle fibres attach to the centromeres of one of the pairs of chromosomes
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The arrangement of bivalents on the equator is random and is an important source of new genetic combinations. What is this known as?
Random assortment
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What happens during anaphase I?
The spindle fibres contract and pull the homologous chromosomes apart, one pair is pulled to one pole and the other pair to the opposite pole
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What happens during telophase I?
Spindle fibres disappear, nuclear membrane reforms, cytokinesis begins
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What happens during meiosis II?
(Repeat mitosis but the end result when cytokinesis occurs there are four haploid cells each with half the number of chromosomes of the parent cell
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What is the significance of meiosis?
Results in the production of haploid gametes which will lead to variation of offspring, contributes to variation by chiasmata formation and crossing over as well as random assortment of chromosomes
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Why is variation essential?
It is essential for the survival of species because if there were to be a environmental change e.g. a disease, if all individuals were identical they may all be killed
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Card 2

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What does meiosis produce?

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Cells that are genetically different to the parent cell

Card 3

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How many chromosomes do the daughter cells of mitosis have?

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Card 4

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How many chromosomes do the daughter cells of meiosis have?

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Card 5

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Why do cells divide by mitosis?

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