GCSE Combined Science revision · Biology: homeostasis, inheritance and ecology

Variation, evolution and breeding

The idea

Variation is caused by genes, the environment or both. Mutations create new variants. Evolution by natural selection: individuals with characteristics best suited to the environment survive and reproduce, passing on their alleles. New species form when populations can no longer interbreed to produce fertile offspring. Selective breeding chooses parents with desired traits over many generations. Genetic engineering transfers a gene from one organism to another, for example the human insulin gene into bacteria.

Describe the variation.
Explain survival and reproduction of the best adapted.
Explain how alleles become more common over generations.

Watch out Individuals do not evolve: populations change over many generations.

See it worked

Worked example

Explain how bacteria become resistant to an antibiotic by natural selection.

A mutation makes some bacteria resistant.
The antibiotic kills the others, so resistant bacteria survive and reproduce.
The resistance allele becomes more common.

Answer Resistant bacteria survive and reproduce, passing on resistance

Your turn

Question 1Calculator allowed1 mark

What is selective breeding?

Question 2Calculator allowed1 mark

Which is a risk of selective breeding?

Question 3Calculator allowed1 mark

Which is an example of genetic engineering?

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