TASK 3 Flashcards
Selection
Natural selection
- individuals that have certain inherited traits tend to survive & reproduce at higher rates –> spread traits that are responsible for it (adaptions)
- population level
- amplify/diminish only traits that differ in individuals of that population
- context dependent
= Heritability + variation + competition (selection)
Reproductive success
- passing genes to the next generation –> they can pass on those genes
- number of offspring produced by an individual + probable reproductive success of those offspring
- mate choice: important factor in this success
Fitness of alleles
- weighted average of the relative productive success of the different phenotypes
- either a genotype or a phenotype
Adaptive evolutionary change
- Evolutionary changes that are adaptive to the given environment
- Such changes increase survival and / or reproduction and are produced by natural selection
Purifying selection
- selective removal of alleles that are deleterious
- can result in stabilizing selection through the purging of deleterious variations that arise
Stabilizing selection
- population mean stabilizes on a particular non-extreme trait value
Directional selection
- an extreme phenotype is favoured over other phenotypes –> allele frequency shifts over time in the direction of that phenotype
Disruptive selection
= diversifying selection
- describes changes in population genetics in which extreme values for a trait are favoured over intermediate values
- variance of the trait increases –> the population is divided into two distinct groups
Mutation-selection balance
- Equilibrium in the number of deleterious alleles in a population
- mutation introduces genetic variation into population while selection reduces it
- level of genetic diversity depends on the relative strength of the two
- -> the more heritable a gene + the more selective pressure the faster selection & evolution
Mechanisms of Maintenance
- -> persistence of variation = why selection may not always eliminate variation
- Heterozygote advantage
- Negative frequency-dependent selection
- Force of mutation
- Inconsistent selection
- Sexuallity antagonistic selection
Heterozygote advantage
- heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype
- often due to overdominance (single locus)
Negative frequency-dependent selection
Frequency-dependent selection = fitness of a phenotype depends on how common it is in the population
- negative: fitness of a phenotype decreases as it becomes more common (fitness high when rare)
- -> The trait is only advantageous as long as it is the minority
- Surprise as advantage (left-handers in interactive sports)
Inconsistent selection
- environment changes fast over a short period of time –> selection that begun must be reversed
- selective optimum moves around from time to time/ place to place (e.g. year of draught)
Sexuallity antagonistic selection
- optimal phenotype for a male is not the same optimum for a female
- -> some alleles that improve fitness of males harm that of females & vice versa
Adaptationist stance
- If some feature or behaviour is commonly found in an organism –> probably an efficient design solution to some problem that that organism has faced
- If it were not, then the alleles building that feature would have been out-competed by alternatives that built a different feature
Phenotypic gambit
= forming adaptationist hypothesis directly about the phenotype
- -> without needing to know what the genetic or developmental mechanisms that produce the phenotype are
- validity of this can not be taken for granted
Ultimate explanation
- WHY that particular design increased ancestral fitness
- evolutionary reason
- ultimate explanation of a characteristic that increased compared to others
Proximate explanation
- HOW: which genetical or developmental mechanisms led to the formation of that characteristic in individual organisms
- underlying mechanisms (e.g. different genes, proteins etc.)