Speciation and Evolution
Speciation: this is the process by which new species arise.
The clips below are a short 5-6 minute explanation of Darwin and Lamark's theories
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Genetic Drift
Genetic drift just is the random change in alleles due to chance.
Due to chance some alleles are lost from a population which will change the genetic makeup of the population. Over a period of time this can result in the loss of some alleles. If only one allele remains in the population, then all the individuals in the population will have that allele and the allele is said to be "fixed" in the population.
When a population is small the effect of genetic drift can be have a much bigger part to play in the speciation process.
Below is a link to a 3 min clip to explain:
Founder Effect
In the Founder effect there is a small population because only a small number of individuals have moved out of an area and have entered into a new location or habitat.
The particular combination of alleles this small group has is slightly different from the combinations of alleles that the original population has.
The small population has less genetic diversity as well.
Founder effect is a case of genetic drift in which rare alleles, or combinations of alleles, occur in higher frequency in a small population which was isolated from the general population.
For example, dwarfism is much higher in a Pennsylvania Amish community compared to the original population of people emigrating from Germany to this area.
Founder effect is evident when organisms move to a new place/island.
The Founder effect is very significant in NZ evolutionary history.
The particular combination of alleles this small group has is slightly different from the combinations of alleles that the original population has.
The small population has less genetic diversity as well.
Founder effect is a case of genetic drift in which rare alleles, or combinations of alleles, occur in higher frequency in a small population which was isolated from the general population.
For example, dwarfism is much higher in a Pennsylvania Amish community compared to the original population of people emigrating from Germany to this area.
Founder effect is evident when organisms move to a new place/island.
The Founder effect is very significant in NZ evolutionary history.
Bottleneck effect
In the case of bottlenecks, the small population size is due to a large number of the parent population being killed off. They may have all been wiped out by a disease, a flood, an earthquake etc.
So in this case, like the Founder effect, the surviving population has a different combination of alleles compared to the parent population. Genetic drift has a larger effect on this small population.
So in this case, like the Founder effect, the surviving population has a different combination of alleles compared to the parent population. Genetic drift has a larger effect on this small population.
The Process of Speciation
How do new species develop from their ancestors?
Genetic variation must exist AND there must be selection pressure. So the environment will act to select for certain alleles.
Over time and generations there will be an increase in isolation of the gene pools. The organisms will no longer mate; there will be reduced gene flow between the populations
Over more and more time/generations the genetic differences will continue to increase and there will be more and more isolation from each other.
As the groups become more and more separated genetically they progress from being one population to 2 populations, then to variants, races and subspecies. Finally they become separate species and can no longer mate and reliably produce viable offspring.
Genetic variation must exist AND there must be selection pressure. So the environment will act to select for certain alleles.
Over time and generations there will be an increase in isolation of the gene pools. The organisms will no longer mate; there will be reduced gene flow between the populations
Over more and more time/generations the genetic differences will continue to increase and there will be more and more isolation from each other.
As the groups become more and more separated genetically they progress from being one population to 2 populations, then to variants, races and subspecies. Finally they become separate species and can no longer mate and reliably produce viable offspring.
This link is to another page which goes into detail on Selection Pressure, what it is and how it works.
This app is a simulation of natural selection in the classically flawed report on the peppered moth in England:
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This clip is a fantastic example of natural selection: the Pocket Mouse; one of my favs!!!
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And then there was...... ISOLATION
“Isolation” basically means that two groups of organisms can’t mate and make offspring anymore. Their gene pools are isolated. There is no gene flow between them. When this happens, speciation has happened or is in the process of happening.
Evidence for Evolution
Two clips here - Khan Academy the quick short version on the left and the longer 45 min version on the right.
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Pass Biology on Speciation:
New Zealand: our own research into evolving enzymes, evolution at the molecular level: