Variation, Natural Selection and Evolution Flashcards
What is (roughly) the theory of evolution?
This is the theory that, over long periods of time, species change as they become adapted to changes in the world around them.
Outline how the process of natural selection works.
- ) Organisms produce large numbers of genetically diverse individuals - more than could possibly survive.
- ) Selective agents in the environment act on this population, selecting for the individuals best suited for survival in that particular environment.
- ) Those best adapted a specific environment survive to reproduction and can thereby pass on their genes to the next generation.
Why is variation important in natural selection?
Without variation between individuals in a population i.e if all members of a population were clones of one another; Natural selection could not take place as there would be nothing to differentiate between those best suited to survive and those least suited to survive. So if a new selective agent emerged the entire population would be wiped out.
What are the two types of variation?
Environmental and genetic.
What is environmental variation?
This refers to differences between individuals which are not inherited.
Give some examples of environmental variation.
Adult weight/height due to differences in food supply
Leaf size due to differences in light level
Stunted Plant growth due to limited access to minerals in the soil.
Scurvy due to Lack of vitamin C
What is genetic variation?
Genetic variation refers to differences between individuals resulting from:
Mutation - which introduces new genes into populations
Meiosis - which shuffles existing genes to produce new, unique combinations.
What type of variation does Natural selection work upon?
Only upon genetic variation. it cannot work upon environmental variation because such differences are not inherited.
What are the two types of genetic variation?
Discontinuous variation and continuous variation.
What are discontinuous variables?
These are features which can only take two forms i.e an either/or situation.
Give some examples of discontinuous variables.
Being able to roll your tongue or not
Height in pea plants.
having attached eat lobes or detached ones.
What is discontinuous variation a result of?
This is a result of just one pair of alleles controlling one feature.
What are continuous variables
These are features which can take on a wide range of forms.
Give an example of a continuous variable.
Height/Weight in humans.
How is continuous variation distributed in most cases for most organisms.
Along a smooth symmetrical curve called a normal distribution.
What is continuous variation a result of?
This type of variation results from many pairs of alleles having an effect on one feature.
What is a selective agent (agencies plural)
This is anything in the environment that acts to select or deselect an individual for survival and, in the end, breeding success.
What are the two types of selective agent?
Density dependent factors
Density independent factors.
What kind of competition is most severe and why?
The most severe form of competition occurs between individuals of the same species - intraspecific competition. This is because members of the same species share almost all features in common and therefore compete for almost all the same things.
What is evolution the result of?
Natural selection working upon genetic variation.
What is the species genome?
This is all the possible alleles for one species in all regions of the world.
What is a population genome?
This is all the alleles present in a population
What is allelic (gene) frequency?
This is the number of times a particular allele occurs any genepool
What effect does natural selection have on the allelic frequency?
Natural selection causes changes in the allelic frequency for all alleles in the species genome. This causes some alleles to become more common and others to become less common and some to disappear forever.
For a allele to be selected for, what must it provide?
An adaptive advantage. i.e the phenotype resulting from this allele must give some advantage which results, in the end, a better chance of surviving to reproduction/
What is genetic drift?
This is the idea that during a species’ time as a small population the species gene pool drifts randomly about because chance events have a much greater effect on the species gene-pool. If this small population gets lucky and the population now booms, the species will now contain genes that have no adaptive advantage
What is speciation?
This is the emergence of new species from ancestral ones.
When does speciation occur and why?
This occurs when a sub-set of the population somehow becomes isolated from the rest for a very long time. This results in speciation because when two populations of a species are separated, genetic variations in one population can no longer be passed on to the other.
What are the types of isolation mechanisms?
Temporal (time) isolation
Geographical isolation
Behavioral isolation
Morphological Isolation
What keeps a species confined to its ecological niche?
Interspecific competition.
What is adaptive radiation?
A new niche becomes available for other species to exploit via species extinction. When a mass extinction event takes place (or a new land mass is formed) the survivors of said event undergo an explosion of evolution and speciation.
