Task 3 Flashcards
What are the two important principles from Malthus’ ‘An Essay on the Principles of Population’?
- Populations could potentially grow exponentially, but in practice cannot do so, thus they must be limited by incomplete survival and/ or reproduction
- Exponential population growth: population increase at an ever-increasing rate -> populations in nature aren’t like this
How is reproductive success defined?
the number of viable descendants produced
What is the fitness of an allele?
The number of copies in the next generation that a copy in this generation leaves -> where there are 2 alleles in competition with one another, their relative fitness determines how proportions change over time
What is the link between natural selection and alleles?
Natural selection changes allele frequencies, increasing the frequency of those alleles with high fitness: The fitness of the allele is the weighted average of the relative productive success of the different phenotypes
What are the different modes of selection?
- Purifying
- Stabilizing
- Directional
- Disruptive
What is purifying selection?
When an allele that does something useful is fixed at a locus. Whenever a mutation arises at that locus, it has lower fitness and is weeded out -> these mutations are called deleterious.
It is an extreme form of stabilizing selection
What is stabilizing selection?
When the current population average of a trait is also the optimum from a fitness point of view. Individuals lower or higher on the trait have reduced fitness.
What is directional selection?
Directional selection is operating whenever the optimum value of the characteristic from a fitness point of view differs from the average value in the current population. Phenotypes that are different from average thus enjoy fitness advantage
What is disruptive selection?
Happens when two extremes of a phenotype are favored relative to the intermediate type from the original population.
What is sustained selection?
Selection, which can delete population variation, driving heritability of the characteristic down towards zero
What is the mutation-selection balance?
Where selection is very strong and sustained,genetic variation can be used up and heritability is zero
What five mechanisms that sustain genetic variation?
- Heterozygote Advantage
- Frequency-Dependent Selection
- Force of Mutation
- Inconsistent Selection
- Sexually Antagonistic Selection
What is the Heterozygote Advantage?
Individuals with one copy of a particular allele have higher fitness that individuals with either 2 or no copies
What is an example of the Heterozygote Advantage?
Sickle-cell disease:
Homozygotes (ss) have abnormalities in their blood cells that cause health problems
Heterozygotes (Ss) have some abnormalities, but not to the extent that they cause health problems
-> for both they are less advantageous for environments with malaria
What is Frequency-Dependent Selection?
A phenotype is associated with relatively high fitness when it is rare, but relatively low fitness when it is common. The result is that the type stabilizes at am intermediate frequency.
How does sexually antagonistic selection sustain genetic variation?
The optimal phenotype may not be the same for males and females. An allele that increases height may be optimal to increase fitness among men, but not in women. Thus we will alway have variation.
What is the idea of the adaptationist hypotheses?
If some feature or behavior is commonly found in a type of organism, then it is probably an efficient design solution to some problem that an organism has faced. If it were not, then alleles building that feature would have been out competed by alternatives that build a different feature.
What is an ultimate explanation?
The explanation of how a particular how a particular design increased ancestral fitness.
-> Why
What is a proximate explanation?
Explanation of the genetic mechanisms that led to the formation of a characteristic.
-> How
What are the four reasons for us to assume that current things are not optimal designs?
- Time Lags
- Selective Regimes
- Genetic Correlations
- Shape of the Adaptive Landscape
What are the three main ways to test adaptive hypotheses?
- Reverse Engineering and optimality models
- Experimental Manipulation and Experiments of Nature
- Comparative Evidence
What are the reverse engineering and optimality models?
Carefully examining how something works and trying to come up with ideas about what function would have led it to be designed that way
What is the Bateman principle?
Male reproductive success increases with each additional partner mated to a greater extebt than is true for females
