Unit 2 AQA Biology - Variation

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What does it mean?
Variation means the differences between living things.
Investigating Variation
Sampling involved taking a selection of individuals from the target population (the population
being investigated). These individuals will represent the population as a whole.
Problems with Sampling:
Sampling Bias: The selection process may be biased. The investigators may be making
unrepresentative choices, either deliberately or unwittingly. Would you measure the daisies
next to cow pat?
Chance: Even is sampling bias is avoided, the individuals chosen, by pure chance, may not
be representative. The 50 daisies you measure may just happen to be the tallest!
Causes of variation:
Mutations: change in base sequence of DNA, however the sudden changes in DNA and
chromosomes may or may not be passed on to the next generation
Meiosis: independent segregation and crossing over and recombination.
Fusion of gametes (fertilisation): fertilisation is a random process
Environmental factors: things such as light intensity, nitrogen, carbon dioxide or things
like diet, exercise and upbringing
Twin studies:
Identical or monozygotic twins have exactly the same genotype so any differences
between them are likely to be due to environment, in other words, their upbringing.
Identical twins reared apart are especially interesting to geneticists.
Non identical twins or dizygotic twins reared together have different genes but
largely the same environment. Any difference between these twins is largely genetic.
It is difficult to draw valid conclusions from twin studies in humans because there are
so few subjects to study. To make the results more reliable we would need random
sampling from a large number of individuals, but there just aren't that many. When
the group being studied is so small chance plays a big part in contributing to
differences between samples.

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Types of variation
Variation exists in tow basic forms:
1. Variation between different species is interspecific variation
2. Variation between members of the same species is intraspecific variation
Intraspecific variation can be either continuous or discontinuous.
Features fall into one category or another like blood group.
Controlled by a single gene or very few (single alleles that you
either have or do not)
Low environmental influence
Can take on any variable i.e. height, shoe size, intelligence.…read more


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