Hardy-Weinberg Flashcards
What is population genetics?
The study of how populations of a species change genetically over time leading the the species evolving
What are the five factors affecting gene frequency?
Natural Selection Sexual Selection Mutation Genetic Drift Gene Flow
What is natural selection and give an example?
Natural selection is the non-random passing of an allele that gives a greater fitness to the individual
Example - Ford (1953), Kettlewell (1955, 1961) Majerus (1998)
Industrial melanism - Changing environment suited melanic Biston betularia and so this gene became more frequent
- Ford; most stiking case of transient polymorphism
- Kettlewell 1955; comparison predation on morphs in polluted vs non-polluted areas
- Kettlewell 1961; first spotted in Manchester 1848 50 years later 95% of population was melanic
What is Sexual selection and give an example
Sexual selection is the passing of a trait that improves likelihood of finding a mate but provides no fitness advantage
Example - Andersson 1994
- Peacock (Pavo cristatus); growing of such an elaborate tail is detrimental to fitness but is desired by females
What is mutation and give an example?
Mutation is a random change in DNA, these changes may provide an advantage or a disadvantage and will subsequently be prolonged or removed by non-random natural selection
Lenski, 1991
- Showed that along random mutations in E.coli could lead to the evolution of new strains better suited to the environment they were cultured in
What is Genetic drift? What are the 2 mechanisms?
- Random fluctuations in the numbers of gene variants in a population
- random increase of decrease of alleles over time
- typically occurs in small populations where infrequently occuring alleles face a greater chance of being lost
- The Founder effect and the Bottleneck effect
What is the founder effect?
Occurs when a few individuals become isolated from a larger population
Different allele frequencies can be seen in smaller founder populations than those in the larger population
What is the bottleneck effect?
A sudden reduction in population size due to changing environment
Resulting gene pool may no longer be representative of the original gene pool
Small populations are further affected by genetic drift
Give an example of the bottleneck effect
Weber et al., 2000
Northern Elephant seal (Mirounga angustirostris)
- rebounded from 20-100 individuals to >175,000 today
- comparisons in historical mDNA to recent mDNA showed that the historical samples possessed additional genotypes to the modern mDNA
What is gene flow?
Changes in genotypes due to mixing with different populations (immigration/emmigration)
What is the Hardy-Weinberg equation?
p^2+2pq+q^2=1
p^2 = frequency of homozygous dominant
2pq = frequency of heterozygote
q^2 = frequency of homozygous recessive
What are the Hardy-Weinberg principles?
- Genetic variation in a population will remain constant from one generation to the next
- Describes a population that is not evolving: both allele and genotype frequencies in a population will remain constant
- If the population does not meet the criteria of the H-W principle it can be concluded that population is evolving
What is the Hardy-Weiberg equilibrium?
The H-W principle states that the frequencies of alleles and genotypes in a populatiion remain constant from one generation to the next
- Allele frequencies will not change in a given population where gametes contribute to the next generation randomly
- Mendelian inheritance preserves genetic variation in a population
- H-W equilibrium describes the constant frequency of alleles in such a gene pool
Give an example of the founder effect
Ramachandran et al., 2005
Humans out of Africa, serial founder effect resulting in dramatic genetic variation
What are the equations p2+2pq+q2=1 and p+q=1 used for?
p2+2pq+q2=1
- used to determine frequency of GENOTYPES in a population
- diploid population = (p+q) (p+q) = 1
- FOIL rule [p2+pq+pq+q2 =1], [p2+2pq+q2 = 1]
p+q=1
- used to determine the frequency of an allele in the population
