Selection and Speciation
- Created by: Anon
- Created on: 23-02-15 16:07
View mindmap
- Selection and Speciation
- Selection
- A condition of the Hardy-Weinburg principle is that 'there is no selection'
- This is highly unlikely to be the case in the real world because some individuals have more reproductive success than others
- Differences in reproductive success affects the allele frequency in the population
- 1.All organisms produce more offspring than can be supported by the environment, causing competition
- 2. In the gene pool there are already many different alleles
- 3. Some alleles may cause an individual to be better suited to the environment, making them more likely to survive
- 4. Individuals with the advantageous allele will then grow faster and be more likely to live longer and pass on that allele
- 5. Over many generations the number of those with the advantageous allele will increase, whereas the frequency of the disadvantageous allele will decrease
- Types of selection
- Directional selection
- Directional selection favours individuals that differ from the mean of the population
- If conditions in the environment change some individuals will have a phenotype that is to the left or right of the mean, making them more likely to survive
- The mean of the population will move in the direction of these individuals over time
- Stabilising selection
- Stabilising selection favours the average individual and so preserves the characteristics of the population
- If environmental conditions remain stable the individuals with phenotypes closest to the mean will be more likely to survive and reproduce
- Stabilising selection tends to eliminate phenotypes at the extremes
- Directional selection
- A condition of the Hardy-Weinburg principle is that 'there is no selection'
- Speciation
- Speciation is the evolution of one species from another species
- Individuals in a single population breed with each other and form a single gene pool
- However, the population may become separated and therefore the flow of genes will cease
- Populations are usually separated by geography, in geographical isolation
- Things such as mountains and oceans cause geographical isolation
- The two populations may then experience different conditions in their separate environments
- Different alleles will be favourable in each of the different conditions and so different phenotypes will be more likely to survive and breed
- Over many millions of years the two populations may become so different that they are unable to interbreed to create fertile offspring. A new species has been formed
- Selection
Comments
No comments have yet been made