Download fact file: genetic diversity

Genetic diversity
How it all begins:
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It’s the differences in DNA that leads to the vast genetic diversity.
Genetic diversity is the variation between genes within specie.
A gene is a section of a DNA that contains coded information for making polypeptides. All
members of the same species have same genes. However it’s just the allele that differs.
Therefore the combination of the different alleles results individuals to be different from
others also known as random fertilisation.
In the process of meiosis and mitosis crossing over of the chromatids allows the exchange
alleles therefore increasing genetic diversity.
Mutation also may cause variation. Mutation is a change in the structure of the DNA; this is
because the base sequences have altered having a knock on effect the on sequence of
polypeptide chains, which means there will be a change in characteristics.
The greater the number of differences the greater the genetic diversity, therefore the specie
will be more likely to adapt to some environmental changes. If these new characteristics
give a selective advantage they will be passed onto the next generation.
Factors that affect Genetic diversity…
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Genetic diversity can also be reduced when specie has fewer different alleles. The 3 main
factors are selective breeding, genetic bottleneck, founder effect and inbreeding.
Selective Breeding
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This is the process where individuals with desired characteristics are used to parent the next
generation.
Selective breeding is commonly carried out in order to produce high yielding breeds of
domesticated animals and plants. This is also called artificial selection.
Eventually by breeding the animals or plants with the desired characteristic’s alleles the
alleles that contain the unwanted characteristics are bred out.
Therefore the variation decreases and the population will eventually only consist of the
desired characteristics.
Examples :
1) In plants such as wheat the factor that considers the ‘desired characteristics’ are having
large grains with a high gluten content, short stems and resistance to disease by
crossbreeding wheat plans with disease resistance.
Figure 1 shows the difference between selective breeding and natural growth.
2) Some chickens have been selectively bred to lay lots of eggs, most are still kept in cages.
Broiler chickens have been bred for meat. They grow twice as quickly and are usually
slaughtered at six weeks old. Most meat chickens are kept intensively in large sheds.
Figure 2 show how the chickens are selectively bred and artificially
induced to yield high egg production
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As efficient as it sounds selective breeding has its cons.
In this case:
PROS
You can get a higher yield of eggs therefore
more can be sold and more profit can be made
for the farmer
It allows us to meet our demands for cheap
plentiful food.
Consistent quality and amount of food supply
CONS
The chickens are kept in a high intensive area,
this will encourage the rate of spread of diseases
and it’s not health at all for the chickens
physically.
Farmers will be under extra pressure due to the
highly competitive market which will encourage
more selective breeding.
Can result in genetic diseases caused by
recessive alleles, therefore the inbreeding will
result in a smaller gene pool, genetic variation
decreases.
Ethical issues involved in the selection of domesticated animals.
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Selective breeding is seen in some way as interfering with nature and compromising the
rights of the animals.
Selective breeding in pets equally as important as selective breeding animals for food.
Balancing the increase in yield with animal welfare; there has to be a point where the
selective breeding of a particular feature before it disables the animals.
Producing genetically uniform livestock’s could result in alleles in being lost which may
possibly beneficial for the animals or even the humans
Founder effect
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A few indivuals might choose to colonise an isolated area; they will move from the original
population to a remote area.
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Figure 3 shows the movement from the original population to the new isolated area
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However the frequency of the alleles may be different from the original population.
Eventually the rare alleles which are recessive are lost reducing genetic diversity.
However a mutation might occur within the new population. If they have a selective
advantage they will be passed onto the next generation.
Figure 4 the new population with different frequency of alleles
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Example :
The fugates of Kentucky
Small founding population on the mountain community. 2 of the founders were carriers for
the proteins that cause blue skin. As they reproduced eventually everyone had blue skin;
they have the phenotype of a blue skin.
Figure 5 Blue skin
Genetic bottlenecking
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This is when ecological events may reduce population dramatically due to catastrophic
events like earthquakes, tsunami or human hunting.
The people have no choice of survival; however those that do survive do not act as an exact
representative either, causing the allele frequency to vary.
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Figure 6 Genetic bottleneck
Example:
Northern elephant seal
After the hunting by mankind during the 1900 only 20 were left on the Mexico coast.
However they did increase over years however there genetic diversity was low compared to
the southern elephant seal.
Figure 7 elephant seal
Figure 8 A graph to show the population size over time
It’s easy to get confused with the both factors:
SIMILARITIES
Both are followed by a genetic drift which results
in the change in the allele frequency.
Variation is lost in both.
Both consists of inbreeding and the formation of
a new population
DIFFERENCES
In the bottleneck situation the people do not
have a choice whether they want to be part of a
new population however in founder effect the
people have a choice.
Bottleneck situation is caused by a catastrophic
event where as founder effect is just a matter of
choice.