Lecture 6 Flashcards
(25 cards)
Ronald Fisher
main focus: selection
- Evolution is mainly driven by natural selection acting on small genetic variations.
Sewall Wright
main focus: drift + selection
- Genetic drift and population structure (e.g., small populations) play a big role in evolution.
Motoo Kimura
main focus: neutral evolution
- Most mutations are neutral (do not affect fitness) and evolve by genetic drift rather than selection.
Tomoko Ohta
main focus: nearly-neutral theory
- Some mutations are slightly beneficial or harmful, meaning both drift and selection influence evolution.
what was the main debate between Fisher & Wright and Kimura & Ohta
- Fisher vs. Wright: Fisher emphasized natural selection, while Wright believed drift played a role, especially in small populations.
- Kimura & Ohta: Challenged the idea that natural selection is always the main driver, proposing that many mutations spread randomly.
What is population genetics?
The study of how alleles are distributed in populations and what causes changes in allele frequencies over time.
What is the Hardy-Weinberg theorem?
A null hypothesis for evolution, stating that allele frequencies remain constant unless acted upon by forces like selection, mutation, or drift.
How does population genetics explain genetic variation?
It studies the maintenance of genetic variation across different times and locations.
What is balancing selection?
A type of natural selection that maintains harmful alleles in a population, like lethal alleles that persist due to heterozygote advantage.
What is a cline in population genetics?
A gradual change in allele frequencies across an environmental gradient (e.g., fur color changes with temperature).
How many alleles does a diploid individual carry at each locus?
two - one for each parent
What does it mean to be homozygous at a locus?
Both alleles are the same (e.g., A₁A₁ or A₂A₂).
What does it mean to be heterozygous at a locus?
The two alleles are different (e.g., A₁A₂).
What does the Hardy-Weinberg Theorem (HWE) state?
If there is no selection, migration, or mutation, allele frequencies remain constant from one generation to the next.
What is the first prediction of HWE?
Allele frequencies remain constant over generations if no evolutionary forces act on the population.
What is the second prediction of HWE?
Genotype frequencies follow the equation:
Nc
the number you count or census
What is 𝐻𝑒, 𝑝, and 𝑞 in Population Genetics?
𝐻𝑒 - expected heterozygosity
p - frequency of the dominant allele
q- frequency of the recessive allele
𝐻𝑒 = 2pq
population bottleneck
occurs when a population’s size is drastically reduced due to an event like a natural disaster, disease, or human activity. This leads to loss of genetic diversity and can impact evolution.
what are the effects of a bottleneck:
- Reduced Genetic Variation – Many alleles are lost, making the population less adaptable to environmental changes.
- Genetic Drift Becomes Stronger – Random changes in allele frequencies have a bigger effect in small populations.
- Inbreeding Increases – With fewer individuals, mating occurs among relatives, leading to harmful recessive traits.
what is Ne
the effective population size
- its the size of an ideal population that would undergo the same amount of genetic drift as the population under consideration
How does population size affect heterozygosity?
Smaller populations lose heterozygosity faster due to genetic drift, reducing genetic variation.
what is Nc
Nc is the census population size, meaning the actual number of individuals in a population that you count
How does inbreeding affect offspring?
It increases the chance that offspring inherit two copies of the same deleterious allele, leading to harmful effects.
