AQA AS Biology Unit 2: Genetic Diversity

AQA AS Biology Unit 2: notes on genetic diversity 

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Genetic Diversity
DNA determines the considerable variety of proteins that make up each organism.
Therefore similarities and differences between organisms may be defined in terms of
variation in DNA.
Gene - a section of DNA that codes for one or more polypeptides.
Genetic Diversity Within a Species Genetic Diversity Within Different Species
DNA varies very little DNA varies greatly
Same genes different alleles Different genes
The more related a species is, the more DNA they share.
Genetic diversity within a species is caused by differences in alleles.
It is the combination of alleles an organism possesses that makes species and individuals
within a species different from one another.
The greater number of different alleles that all members of a species possess the greater
the genetic diversity of that species.
The greater the genetic diversity, the more likely that a species will be able to adapt to
some environmental change.
This is because it will have a wider range of alleles and therefore a wider range of
Genetic diversity is reduced when a species has fewer different alleles.
Genetic diversity within a population is increased by:
Mutations in DNA ­ forming new alleles
Different alleles being introduced into a population

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Factors Influencing Genetic Diversity
Selective Breeding
Selective breeding is known as artificial selection.
It involves identifying individuals with the desired characteristics and using them to parent
the next generation.
Offspring that do not exhibit the desired characteristics are killed, or at least prevented from
In this way allele for unwanted characteristics are bred out of the population.
The variety of alleles in the population is deliberately restricted to a small number of desired
alleles.…read more

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The Founder Effect
The founder effect occurs when just a few individuals from a population colonise a new
These few individuals will carry with them only a small fraction of the alleles of the
population as a whole.
These alleles may not be representative of the larger population from which they came.
The founder effect is often seen when new volcanic islands rise out of the sea.…read more

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Genetic Bottlenecks
A genetic bottleneck is an event that causes a big reduction in a population.
Sometimes the reason for this drop is a chance event, such as a volcanic eruption or
interface by man.
The few survivors will possess a much smaller variety of alleles than the original population.
This means the genetic diversity will be less.
As these few individuals breed and become re-established, the genetic diversity of the new
population will remain restricted.
This effect can be illustrated by elephant seals.…read more

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Ethics of Selective Breeding in Domesticated
Almost all scientific progress has both benefits and risks.
Scientists carry out research into various techniques of selective breeding from which they
can report on the benefits and risks of each.
Interested parties, such as government agencies, farmers, food producers, supermarkets
and shopkeepers, and organisations such as animal welfare groups, can then debate the
issues surrounding these reports.…read more

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Ethical Implications
Is selective breeding interfering with nature?
Do other species have rights?
Should the development of new varieties be allowed to take place naturally, as it has
successfully done for millions of years?
Do domesticated animals have value in themselves or only in terms of usefulness to
Should we accept a lower standard of living in return for natural rather than artificial
breeding of animals?
What features should be selected for and who decides?
Is selective breeding of pets equally acceptable as selecting…read more

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Selective Breeding in Cattle
The breeding of farm animals, such as cattle, has never been a random affair.
Farmers have chosen the most suitable domesticated animals and plants to parent the next
Selective breeding is therefore not new but traditional forms of selective breeding are slow
and imprecise.
As consumers we want a reliable supply of a wide range of foods at minimum cost.…read more


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