Meiosis and Mitosis

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Define: Mitosis
Asexual cell division where two identical cells are formed
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Define: allele
a version of a particular gene
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Define: Meiosis
The two-stage process of cell-division which reduces the chromosome number of the daughter cells. It is involved in the making of gametes for sexual reproduction
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Define: Gamete
sex cell which has half the chromosome number of an ordinary cell (ordinary=46)
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A short section of DNA carrying genetic information
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Define: Chromosome
a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
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Why do cells need to be replaced?
New cells are needed for an organism/part of an organism to grow and they are also needed to replace worn out and damaged cells/tissue
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Why do most new cells need to be the same?
Because they need to do the same job as their parent cell, so must carry the same genetic information
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How many chromosomes are in the nucleus?
46 chromosomes arranged in 23 pairs and one of each pair is inherited from your father and one from your mother
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How many chromosome do gametes have?
one of each pair of chromosomes
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What does mitosis result in?
All your normal cells having the same chromosomes and therefore the same genetic information
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What happens in asexual reproduction?
the cells of the offspring are produced by mitosis from the cells of their parent. They contain exactly the same alleles as their parent with no genetic variation
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How does mitosis work?
1) Before the cell divides, it produces new identical copies of the chromosomes in the nucleus. 2)the cell divides to form two genetically identical cells
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What does a normal body cell have?
4 chromosomes in 2 pairs
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What happens when a cell divides into two during mitosis?
forms two daughter cells, each with a nucleus containing 4 chromosomes identical to the parent
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Example of quick cell division
the skin, constantly lose skin cells and replace them rapidly
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Define: Stem Cell
Undifferentiated cell with the potential to form a wide variety of different cell types
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In most animals, when do cells become specialised?
At a very early stage of life
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Define: adult stem cell
Adult stem cells are undifferentiated cells found throughout the body that divide to replenish dying cells and regenerate damaged tissues. Also known as somatic stem cells, they can be found in children, as well as adults.
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Why is growth in a mature animal mainly restricted?
Restricted to replacement and repair. Once a muscle cell, always a muscle cell
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How long are most plant cells able to differentiate?
Throughout their entire lives. You can move a plant cell from one part of the plant to the other and it can redifferentiate
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Define: Cloning
The production of offspring which are genetically identical to the parent organism
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Why is it easier to clone with plants than animals?
Because plant cells can differentiate constantly, whereas animal cells differentiate permanently (clones can be made of embryos)
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What are the female and male gametes and where are they made?
Called ova and made in the ovaries = female Called sperm and made in the testes=male
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What are the gametes formed by and how?
Meiosis reduces the chromosome number by half
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How is the chromosome number reduced by half?
1)Chromosomes are copied so that there are 4 sets of chromosomes (same as mitosis) 2)Cell divides twice in quick succession to form four gametes, each with a single set of chromosomes
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Are all gametes the same?
No. They contain random mixtures of the original chromosome pairs and this introduces variety
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Why does fertilisation add more variety?
Each gamete has a single set of chromosomes and when they fuse to produce a new body cell with 46 chromosomes in 23 pairs. The combination of genes on the chromosomes for every new cell is unique
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What happens once fertilisation is complete?
the unique cell begins to divide by mitosis to form an individual
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Why are offspring of meiosis unique?
The combination of genes in the new pair of chromosomes will contain alleles from each parent. This produces variation in the characteristics of the offspring
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Define: allele


a version of a particular gene

Card 3


Define: Meiosis


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Card 4


Define: Gamete


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