1. Processes of Evolution
AS – (3.5)

2. Processes of evolution
Biological evolution = genetic change in a population from one gen. to another.

3. Processes of evolution
Biological evolution = genetic change in a population from one gen. to another.
Species – a group of organisms that interbreed to produce fertile offspring.

4. Processes of evolution
Biological evolution = genetic change in a population from one gen. to another.
Species – a group of organisms that interbreed to produce fertile offspring.
Speciation – formation of a new species, the result of reproductive isolation.

5. Processes of evolution
Biological evolution = genetic change in a population from one gen. to another.
Species – a group of organisms that interbreed to produce fertile offspring.
Speciation – formation of a new species, the result of reproductive isolation.
Population – members of a species that live in the same geographical area.

6. Processes of evolution
Biological evolution = genetic change in a population from one gen. to another.
Species – a group of organisms that interbreed to produce fertile offspring.
Speciation – formation of a new species, the result of reproductive isolation.
Population – members of a species that live in the same geographical area.
Gene pool – total number of alleles that occur in a population. Changes in the allele freq. show that evolution is occurring.

7. Processes of evolution
Freq. of an allele in a gene pool = occurance of that allele in the gene pool total number of alleles in that gene pool

8. Demes
Deme – a local population that has no or limited gene flow with members of other populations.

9. Demes
Deme – a local population that has no or limited gene flow with members of other populations.
Local natural selection means that phenotypic features (what they look like) of one deme will vary from the next.

10. Demes
Deme – a local population that has no or limited gene flow with members of other populations.
Local natural selection means that phenotypic features (what they look like) of one deme will vary from the next.
When a species has a lot of space, variation may occur along a gradient from one point of the range to another point = cline.
(diagram from pg 205)

11. Demes
Deme – a local population that has no or limited gene flow with members of other populations.
Local natural selection means that phenotypic features (what they look like) of one deme will vary from the next.
When a species has a lot of space, variation may occur along a gradient from one point of the range to another point = cline.
Clinal variation can be linked to either:
environ. differences – cline is purely phenotypic
Due to genetic differences resulting from selection

12. Ring species
A special case of cline where the 2 ends meet to form a loop.

13. Ring species
A special case of cline where the 2 ends meet to form a loop.

14. Gene Flow
Migrate – move between populations and interbreed = introducing new alleles into the populations.

15. Gene Flow
Migrate – move between populations and interbreed = introducing new alleles into the populations.
This is gene flow – an important source of genetic variation where natural selection can act upon.

16. Gene Flow
Migrate – move between populations and interbreed = introducing new alleles into the populations.
This is gene flow – an important source of genetic variation where natural selection can act upon.
Immigration – moving into a population
Emigration – moving out of a population

17. Gene Flow can…
Increase genetic differences between populations – significant if a barrier isolates populations once migration has happened so no further gene flow can occur.

18. Gene Flow can…
Increase genetic differences between populations – significant if a barrier isolates populations once migration has happened so no further gene flow can occur.
Decrease the genetic differences – if migration is regular and involves large numbers, genetic differences between populations can be reduced by gene flow.

19. Gene Flow can…
Increase genetic differences between populations – significant if a barrier isolates populations once migration has happened so no further gene flow can occur.
Decrease the genetic differences – if migration is regular and involves large numbers, genetic differences between populations can be reduced by gene flow.
Gene flow may advantage one population by new beneficial alleles, but it can also harm another due to problems associated with hybridisation.

20. Gene Flow can…
Increase genetic differences between populations – significant if a barrier isolates populations once migration has happened so no further gene flow can occur.
Decrease the genetic differences – if migration is regular and involves large numbers, genetic differences between populations can be reduced by gene flow.
Gene flow may advantage one population by new beneficial alleles, but it can also harm another due to problems associated with hybridisation.
EG – Pied and black stilts. Pied are critically endangered because black due to predators but also hybridisation with eachother.

21. Genetic drift
A change in allele freq. due to the affect of chance over generations.

22. Genetic drift
A change in allele freq. due to the affect of chance over generations.
Occurs in small populations and with alleles not greatly affected by selection.

23. Founder effect
When a small number of animals/plants are dispersed to somewhere away from similar species, they only carry a small number of the genes of that gene pool.

24. Founder effect
When a small number of animals/plants are dispersed to somewhere away from similar species, they only carry a small number of the genes of that gene pool.
The alleles of the colonisers are only a sample of the parent gene pool.

25. Founder effect
When a small number of animals/plants are dispersed to somewhere away from similar species, they only carry a small number of the genes of that gene pool.
The alleles of the colonisers are only a sample of the parent gene pool.
It is a matter of chance which alleles are present in the gene pool. However, over a long period of time, mutation will gradually increase diversity.

26. Bottleneck effect
Occurs when a large population is suddenly reduced in size – result of either a catastrophic event (fire, flood etc) or human impact.

27. Bottleneck effect
Occurs when a large population is suddenly reduced in size – result of either a catastrophic event (fire, flood etc) or human impact.
May randomly affect allele freq. and/or remove alleles so when the population recovers, allele freq’s may not be representative of the original population.

28. Bottleneck effect
Occurs when a large population is suddenly reduced in size – result of either a catastrophic event (fire, flood etc) or human impact.
May randomly affect allele freq. and/or remove alleles so when the population recovers, allele freq’s may not be representative of the original population.
Lack of diversity in small populations increase the likelihood of extinction due to a change in environment.