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Summary notes on Genetic Diversity and Adaptation - AQA A Level
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Genetic diversity and adaptation – AQA A Level Biology Summary NotesGenetic diversity
- Total number of different alleles of genes in a population
Population
- Group of individuals of the same species that live in the same place and can interbreed
Note: larger populations tend to have greater genetic diversity
Gene pool
- All the alleles of all the genes in a population at a given time
Allele frequency
- How often an allele appears in the gene pool
Genetic diversity is a factor enabling natural selection to occur
Because it increases the likelihood that should an environmental change occur, some individuals will
be well adapted to the environment
Natural selection
1. Gene pool of population contains wide variety of alleles
2. Many random mutations within gene pool are harmful. However random mutations may
result in in new alleles of a gene that benefit the possessor
3. This may advantage some individuals over others in the population as they are better
adapted
4. These individuals are better able to survive a selection pressure and have increased
reproductive success
5. Individuals that survive go to reproduce successfully and advantageous alleles are inherited
by next generation
6. As a result, over many generations, the new allele increased in frequency in the population
Natural selection results in species that are better adapted to their environment
Adaptations
1. Anatomical – adaptations affecting physical features (eg fur thickness in arctic foxes)
2. Physiological changes – changes in functioning mechanisms of an organism (eg the ability for
kangaroo rats to oxidise fat rather than carbohydrate to produce extra water)
3. Behavioural – changes to behaviours (eg autumn migration of swallows from UK to Africa)
Selection
- Process by which organisms that are better adapted to their environment tend to survive
and breed
Stabilising selection
- If environment stays stable, individual with the phenotype closest to the mean/average is
favoured – their alleles are passed on
- Eliminates phenotypes at extremes as those are selected against
, - Example: human birth weights
However, if there is a BIG environmental change, there may be no phenotype suited to the new
conditions, in which case the population would die out
Disruptive selection
- Favours two separate extreme phenotypes
Directional selection
- Selection favours individuals that are at the extreme of the population
- This changes the characteristic of the population
- Example: evolution of wide-spread antibiotic resistance in bacteria (antibiotics are drugs that
kill bacteria)
1. Frequent use of antibiotic creates selection pressure
2. Bacteria with a mutation conferring resistance to that antibiotic have selective advantage
over others
3. These bacteria survive and reproduce more than other types and pass on advantageous
allele conferring resistance to their offspring
4. Frequency of advantageous allele (and therefore resistant bacteria) increases in subsequent
generations
5. Process repeats over many generations
Points to note:
- Bacteria develop resistance to any individual antibiotic in isolation to any other antibiotic. Eg
a bacterium may be resistant to penicillin (one antibiotic) but susceptible to tetracycline
(another antibiotic)
- Mutations are random – antibiotics do not cause mutations
RP6: Use of aseptic techniques to investigate the effect of anti microbial substances on microbial
growth
Method:
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