TS5: Evolution Flashcards
Which is more important: genetic stability or genetic plasticity? [Give key points for both arguments]
Stability:
- DNA repair
- Accurate cell division
- Passing genes to offspring
[Altruistic behaviour]
Plasticity:
- Adapt to new environments
- Survival
What is a hypermutator allele, and why might this impact the theory behind molecular clocks?
A hypermutator allele is a genetic mutation that increases the rate at which mutations occur in an organism’s DNA e.g., hitting the fidelity of DNA replication.
This means cells have increased genetic variation due to the hitchhiker hypermutator allele, and so the rate of spontaneous mutation will not be constant throughout the population.
What are the 4 key points in Darwin’s theory of evolution?
- Descent with modification
- Random variation
- Struggle to survival (selection pressure)
- Survival of the fittest
How did Darwin come up with the idea of descent with modification?
Whilst looking at pigeons, he realised there’s a tendency for offspring to resemble their parents, but not be identical to them. E.g., all pigeon variations descended from the common rock dove.
Define evolution.
Species changing over time.
[NB: there’s no reference to a mechanism of how this is achieved]
Define natural selection.
The differential survival and/or reproduction of classes of entities that differ in one or more characteristics, and this difference cannot be due to chance.
Describe the problem of inheritance.
Darwin’s theory of natural selection seemed to go against Mendel’s theory of inheritance: Darwin’s proposed small changes as the source of variation for natural selection, but Mendel argued inheritance was binary, based on the laws of dominance and recessivity.
We now know that genetic variation can produce apparently blended inheritance and continuous, small variation due to multigene traits.
State the Hardy-Weinberg equation and its 4 key assumptions.
Why is it still important today, despite these assumptions?
p^2 + 2pq + q^2 = 1
where p is the frequency of the dominant allele, and q is the frequency of the recessive allele.
Assumptions:
1. Infinite population size
2. No mutations or migration
3. Mating is random
4. No natural selection (all genotypes have an equal chance of survival and reproductive success)
It shows that recessive alleles can be maintained in a population.
Define the ‘fundamental theorem’ of natural selection.
Give the equation that describes this.
Changes in the average level of fitness in a population can be predicted by looking at the amount of genetic variation that contributes to fitness, assuming that the environment remains stable.
This genetic variation is typically referred to as the “additive genetic component of fitness,” and it refers to the genetic variation that is passed down from parents to offspring and that contributes to differences in fitness between individuals.
dM/dt= W –E – M/C
What was Malthus’ theory, and how did it inspire Darwin?
Economist Thomas Malthus explained that while population growth was exponential, resource growth was linear.
This inspired the competition for resources behind Darwin’s theory.
What is the Modern Synthesis? What are the 4 key pillars that it’s based on?
Also known as Neo-Darwinian synthesis, is a scientific theory that integrated Darwin’s and Mendel’s ideas of evolution and inheritance.
It’s based on 4 key pillars:
1. Natural selection is the primary mechanism for evolution of species.
2. Evolution occurs through changes in gene frequencies in populations over time.
3. Genetic drift causes evolution in small populations.
4. Speciation occurs through accumulation of genetic differences between populations over time.
Define major allele frequency (MAF).
The frequency at which the most common allele occurs in a population.
What is Hamilton’s law? Give the equation related to this theory.
Explains that altruistic behaviour can evolve by natural selection if the cost to the individual is outweighed by the benefit of a close relative.
rb > c
r = relatedness of the individual to the relative
b = benefit to the recipient
c = cost to the actor (individual)
What is inclusive fitness?
A measure of an individual’s overall reproductive success, including both their own direct reproductive success and the reproductive success of their close genetic relatives.
Describe the neutral theory of evolution.
Suggests that most evolutionary changes at the molecular level are due to random genetic drift rather than natural selection.
Most mutations have little or no effect on fitness, becoming fixed by random genetic drift.
- Rate of evolution is determined by the rate of mutations occurring, not the rate of selection.
Define genetic drift.
The random fluctuation of gene frequencies over time due to chance events such as reproduction and death.
Define fixation (in reference to an allele).
When all individuals within a population have that allele, it has become fixed.
State the formula that describes fixation within neutral evolution i.e., heterozygosity at time t, and give its implications.
Ht = H0 x (1-1/2N)^t
where H0 is the starting heterozygosity.
- As t gets bigger, the eventual result is that Ht = 0, so the probability of fixation is equal to initial frequency…
- BUT, the large the population size N, the longer the time that is will take for 1. to occur.
