Natural Selection I Flashcards
Lesson 9
What is the Hardy-Weinberg Principle?
p^2 : 2pq : q^2
How does loci achieve Hardy-Weinberg Equilibrium?
When the genotypes at a locus have the frequencies predicted by the H-W principle.
What are the assumptions of the Hardy-Weinberg Principle?
- there is no mutation
- Mating among individuals is random (or inbreeding)
- The population is infinitely large (or random genetic drift)
- Individuals are not moved into or out of the population (or gene flow/migration)
- All individuals have equal probabilities of survival and of reproduction (or natural selection)
What is sorting?
beneficial alleles are favored by natural selection, whereas deleterious ones are removed
Is the outcome of natural selection random?
No, because of the idea of sorting
How are adaptive evolutions formed?
natural selection consistently increases the frequencies of alleles that provide reproductive advantages
(continuous process b/c environment can change)
What are adaptations?
traits that have evolved through the mechanism of natural selection
What is the relationship between allele frequency and strength of selection?
Changes in allele frequency are proportional to strength of selection
What does natural selection do?
Increases the frequencies of alleles that enhance survival and reproduction
What are the three modes of natural selection?
directional selection: favors individuals at one end of the phenotypic range
disruptive selection: favors individuals at both extremes of the phenotypic range
stabilizing selection: favors intermediate variants and acts against extreme phenotypes
How does directional selection changes the average value of the trait?
Causes a change in the mean value of a character in a population that is higher/lower than its current mean value
(ex: small seed environment; beak length)
How does disruptive selection increases variation in the trait?
Disruptive selection increases variation by favoring extreme phenotypic values, even if the mean of the distribution doesn’t change
(ex: large + small seeds and beak size)
How does stabilizing selection REDUCE variation in the trait?
Stabilizing selection decreases variation and stabilizes the mean of a trait in population around a particular, usually optimal, value
(ex: neonatal deaths and birth rates)
What is fitness?
The contribution an individual makes to the gene pool of the next generation
What is relative fitness?
contribution of a genotype to the next generation, compared with contributions of alternative genotypes for the same locus.
The relative fitness (W) of the most fit genotype in a population is 1.
