Non-Adaptive Evolution Flashcards
What are the 3 forces of Non-adaptive Evolution
Mutation - changes to DNA, particularly those in the germ line
Gene Flow - migration of individuals and, thus, alleles in and out of a population
Genetic Drift - chance fluctuations of allele frequencies between generations
What is Non-adaptive evolution
Evolutionary changes can arise without generating adaptations
Specifically there are 3 forces
What can mutations do the Allele frequencies
Germ line mutations can essentially instantaneously change population allele frequencies:
- creating more gene copies of existing alleles (Altering p, q)
- Altogether new alleles (p, q, r)
How can Gene flow affect Allele Frequencies
Population allele frequencies can change due to individuals entering or leaving a population
ex:
If you had a population of mice living on Vancouver Island with a high frequency of alleles leading to dark fur.
If a small number of mice were accidentally introduced to Texada Island (which was absent of mice).
Changes are that a subsample of the population will not have the same allele frequencies as on Vancouver Island.
Even under random mating, after generations, it could be that population size on Texada grows with a much large representation of white fur phenotypes than on Vancouver Island.
However this difference may be simply the result of genetic drift and an example of the ‘founder effect’
What does genetic drift do
One way to think about genetic drift is that it typically results in random increases/decreases of gene copies (changes in p and q) in the next generation.
what can genetic drift lead to in some cases regarding diversity
In some cases, alleles can be removed altogether (p=0) resulting in fixation (q=1) regardless of their phenotypic/fitness effect
Alleles can be lost permanently and the evolutionary possibilities for that population/lineage are forever altered
what are the four main points of genetic drift
- generates random changes in allele frequencies across generations
- Relative impact/importance is dependent on population size (more influential in small populations or sever bottlenecks)
- Tends to reduce genetic variation in populations (an allele can be permanently lost)
- Can generate non-adaptive evolutionary change (even non-beneficial alleles can become fixed)
what are the 2 definitions of evolution
- Evolution is the change in the average value of a genetically based characteristic over time
- Evolution is the change in allele frequency over time
what is the founder affect
If a small group of animals colonize a new habitat and are isolated to a degree, their allele frequencies are unlikely to be identical to their original population.
since a subsample of a population is unlikely to have exactly the same phenotype, genotype, or allele frequencies as the whole population.
The founder affect is when a small group colonize and found a new population (often with different allele frequencies)
how can genetic drift operate with neutral mutations
Random changes can accumulate and differences are proportional to time elapsed.
Some mutations are neutral; others have negligible effects on the proteins they code.
Some of these molecular genetic characters are used in building phylogenies, and ‘molecular clocks’ precisely because they evolved largely due to genetic drift (evolution proportional to time)
how does population size influence genetic drift
Relative impact/importance is dependent on population size (smaller = more impact)
Smaller populations experience more genetic drift. Happens due to severe “bottlenecks” or a population established by few founders. Less individuals results in less diversity
explain fixation and when its more likely to happen soon
Chance of permanent loss of alleles in a population of sample of any finite size.
The probability of fixation of an allele is simply its starting frequency
The expected time until fixation (due to chance) is inversely proportional to allele frequency
In theory all populations should hit fixation at some point. Smaller populations tend to hit it faster, populations with an allele with high frequency tend to hit it faster
how can genetic drift leading to negative adaptations
Can generate non-adaptive evolutionary change (alleles can become fixed: p or q = 1.0)
This means that even alleles that are selectively favoured can be lost due to chance. (Many beneficial mutations never spread)
what is the effect of genetic drift in a lineage, and across lineages
Genetic drift (plus new mutations) alone can generate a considerable amount of trait evolution.
But over multiple lineages the average affect is 0
On average genetic drift has no effect on mean phenotypes, but expect lineages do differ. (among lineage variance, proportional to time elapsed)
what can genetic drift be used to generate
Although genetic drift is not a good general explanation for the evolution of diversity genetic drift is often used to generate the biological null expectation.
