Biology B1.7 Genetic variation and its control

All the basic information you need for AQA triple science, taken directly from the specification.

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Genes carry information from parents. They are passed on in gametes (sex cells) and carried on chromosomes. They control our characteristics.

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There are only a few features which are entirely inherited - eye colour, genetic diseases, blood group and hair colour. There are many environmental features such as skin colour, IQ, diseases, hairstyles, tatoos and scars.

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Sexual reproduction

In this type of reproduction there are two parents so therefore there is variety in the offspring. The plant gametes are the egg cell and pollen, and the animal gametes are the egg cell and sperm. An advantage of sexual reproduction is that the species can adapt to survive, but a disadvantage is that it relies on gametes meeting.

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Asexual reproduction

This involves just one parent so there is no variety in the offspring. The offspring are known as clones. Asexual reproduction occurs mainly in bacteria, cells, small animals and plants such as the strawberry plant. An advantage is that it is very safe as there is only one parent, but a negative is that the species cannot adapt to survive.

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A cutting is taken from a plant and dipped in hormone powder. This then grows roots and develops into an identical plant. It is cheap, but you only produce one plant per cutting.

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Tissue culture

A small group of cells is taken from a plant, and grown in a lab. This is good because it produces lots of plants, but it is quite expensive.

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Embryo transfer cloning

Using cows as an example:

Cow A is injected with FSH (fertility drugs). Lots of eggs are harvested and fertilised in the lab. They are then placed in Cow B, creating lots of Cow Cs, with half the DNA from Cow A, and half from the sperm donor.

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Adult/Fusion cell cloning

Using sheep as an example:

The nucleus from the cell of Sheep A is fused with a cell body from Sheep B. This creates Sheep C, who is identical to Sheep A.

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Advantages of Genetic Modification

  • Genetically engineered pest resistance
  • Genetically engineered herbicide tolerance
  • Extra nutritional crops
  • Withstanding drought or high salt
  • Cold tolerance
  • Genetically engineered disease resistance
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Disadvantages of Genetic Modification

  • Costly for companies and customers
  • Insects may develop pest resistance
  • Genetically engineered herbicide tolerance may pass on to weeds
  • Allergy risks
  • Unknown effects on human health
  • May harm organisms that feed on it
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