8 Natural Selection Flashcards
What is the basic idea of natural selection?
Better adapted individuals survive longer so leave more offspring
What conditions are necessary for selection?
1) Variation - in traits
2) Heritability - inheritance of variation
3) Competition & fitness - limited resources available so not all individuals able to survive and reproduce
What are the types of variation?
Continuous - e.g. body size
Discreet - e.g. 2 different colours
What is the gene frequency in Mendelian Inheritance?
0.5
Mendelian inheritance does not produce a directional change in gene frequency
What is ecological competition?
The consequence of limited amounts of resources e.g. food, water, shelter, mates for growth, survival and reproduction
Direct relationship between amount of resource captured and fitness
What is fitness?
A measure of the reproductive success of an individual
If an individual passes on copies of 100% of their genes, fitness = 1 (for diploid 2 offspring needed to achieve this)
What is an example of natural selection in wild populations?
Peppered moth
- Variation between individuals
- Some are better adapted, darker colours in urban areas and lighter colours in rural areas
- These more likely to survive and reproduce, passing on genes
- Reduction in frequency of less advantageous phenotypes
When does selection occur?
When genotypes differ in their ability to pass genes on to the next generation
Successful genotypes will increase the frequency of its genes
What is directional selection?
Selection generates a long-term change in a trait
- Pushes traits in one direction or another
What is stabilising selection?
Selection against extreme trait values
- Leads to reduction in range of trait values
What is disruptive selection?
Selection for multiple optimum trait values
