Variation - Revision Notes for GCSE B1

For AQA spec B1 - concise revision notes.

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  • Created on: 22-06-11 09:42
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Variation, Evolution and Pollution
Inherit genetic info from parents through sex cells (gametes)
Cell -> Nucleus -> Chromosome -> DNA -> Genes
In the 1950s James Watson and Francis Crick attempted the first model of DNA and came up
with the double helix shape we are familiar with today.
Sexual reproduction involves the combination of different genetic information, and so
offspring have much more variation.
Asexual reproduction means the exact same genetic info is passed on, so the offspring are
Different versions of the same genes are called alleles.
Taking cuttings involves taking a small part of the plant and reproducing it in the right
conditions. It is cheap, but doesn't have a great yield.
Tissue culture involves taking a tiny piece of plant tissue then growing it in the right
conditions with the right hormones. It produces thousands, but is very expensive.
Embryo Cloning: give a top quality cow fertility hormones to make her produce a lot of eggs.
Then fertilise the eggs using sperm from a really good bull. Then divide the embryo into
several individual cells, so each cell grows individually. Transfer embryos to host mothers ­
identical calves are born.
Fusion Cell Cloning: nucleus taken from adult cell, and nucleus removed from egg cell from
another animal of same species. Nucleus from original adult cell is placed in empty egg and
new cell given tiny electric shock. This fuses new cell together and starts meiosis. An embryo
develops, which is genetically identical.
Adult cell Cloning: when a new animal is produced this is called adult cell cloning. A big hope
of this is to get desired products, e.g. milk from cows. However some disadvantages include
whether this will lead to `designer babies'. Also the clones will all be susceptible to the same
Genetic engineering involves changing genetic material of organism. Take a small piece of
DNA ­ a gene from one organism and transfer it to a completely different organism. Often a
great benefit is that it can make exactly the protein needed, but a disadvantage is that some
are concerned about health of eating GM crops and would people want to manipulate
humans in the same way?

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Lamarck's theory: Inheritance of acquired characteristics meant that useful changes
developed by parents during their lives to help them survive are passed to their offspring.
Charles Darwin's theory: in 1831 he set out to the Galapagos Islands, and saw that the birds
were variations in terms of their beaks. This brought about natural selection, which meant
that those that were the `fittest' were most likely to survive.
New forms of genes result from changes in existing genes.…read more



A well written set of key points on variation, evolution and pollution which could be teamed up with some flashcards and a quiz or two to make a useful set of resources.

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