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GCSE Biology Summary Notes Variation and Evolution
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Summary Notes on the GCSE Biology topic Variation and Evolution, specifically curated for the AQA Biology Exam Board.
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Variation and EvolutionVariation
Differences in characteristics or variation can be due to genes you have inherited (blue
eyes), environmental causes (liking Ackley Bridge) or a mix of both (buttercup colour).
Genetic variation in a species is due to mutations that have occurred. A mutation is a
random error occurring in bases.
Characteristics that show a lot of variation are often controlled by both the genes you have
inherited and your environment.
Bar Charts and Histograms
We use bar charts to present discontinuous variation.
We use histograms to present continuous variation.
Investigating Variation
Variation within a species can be investigated. To see if there’s a link between the length of
a pea pod and the number of seeds inside the pod:
1) Pick 20 non-biased, random, exposed to equal wind, sun and water pea pods.
2) Using a ruler, measure the length of each pea pod and record in a table.
3) With a small scalpel horizontally slice open the pea pod and count the number of seeds.
4) Repeat three times, discard anomalies and calculate a mean.
5) Put the data into a scatter graph and look for a correlation between the two variables.
Control Variables:
- same type of peas
- peas exposed to same environment
- same aged peas
Repeating the experiment and using a large sample size makes the results reliable.
Natural Selection
Natural selection is organisms with characteristics best suited to their environment are
more likely to survive, reproduce and pass on their useful characteristics via their genes,
survival of the fittest.
1) There is a phenotype variation in a population due to mutations.
2) Those best adapted to the environment will be more likely to survive.
3) And successfully reproduce.
, 4) And pass on their genes for the useful characteristic to the next generation.
There is a phenotype variation in a population due to mutation which means the giraffe has
a longer neck. The giraffe is best suited to its environment because it can reach the higher
leaves and is therefore more likely to survive. This giraffe will successfully reproduce. This
passes their gene for the useful long neck characteristic to the next generation.
Evolution
Evolution is the theory that all things living on Earth today evolved from similar life forms
over millions of years.
Charles Darwin
Charles Darwin is famous for the Theory of Evolution and Natural Selection (survival of the
fittest). He dedicated his life to studying plants and animals and believed that the desires of
animals have nothing to do with how they evolve. He said that organisms, even of the same
species, are different in some ways, and over time those creatures which are adaptable,
survive, while those that do not adapt to changing conditions, such as climatic and
environmental change, do not live to breed and pass on their genes.
He concluded that there was a variation of physical and behavioural features within a
species. Organisms which had features that helped them to adapt to their environment and
circumstances had a better chance of survival than individuals who lacked these features.
These adaptable organisms survived to breed and produce offspring which generally
inherited the “successful” feature of their parents. He called this process “natural selection”.
Darwin knew that organisms evolved and changed from generation to generation, but didn’t
know how these traits were passed on. Only after more was understood about genetics, was
this explained. Darwin also suggested that each species evolves of time and adapts to the
environment in which they live. Thus, the same species living in different environments will
evolve differently and become more and more differentiated over time. He believed that all
species of life on Earth are interrelated and have a common ancestor.
One piece of evidence that helped Darwin develop his theory of natural selection was the
evolution of different beak shapes in the different finch species on the Galapagos Islands.
The explanation of the evolution of the different beak shapes helped convince other
scientists about the theory. Different animals are adapted and suited to different
environments. When Darwin visited the Galapagos Islands, he saw that finches with
different beaks lived on different islands that had different food sources.
There is a phenotype variation in the finch population due to a mutation which means the
finches have different shaped beaks. The finch is best suited to its environment because it
can eat the specific food on the island which enables them to survive. This finch will be more
likely to reproduce and pass on the useful gene. Gradually every finch on the island would
be born with the adapted beak.
His theory was slow to be accepted:
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