Lecture2: Evolution and Natural Selection

List the requirements for evolution by natural selection to occur (i.e.

“Darwin’s three conditions”)

1.  A population has variation in a trait.

2. That variation is heritable.

3.  Some variants are better able to survive and reproduce than others (i.e. have higher fitness).

1. Does natural selection always result in the ideal phenotype?

Natural selection does not always result in the “ideal” phenotype. It Favors individuals with highest fitness relative to others in population

Natural Selection:

a non-random process of evolution that favors individuals that survive and reproduce

Fitness:

relative contribution of an individual to the  gene pool of the next generation

Fitness measure:

 (= relative reproductive success) relative number of offspring that survive and reproduce. fitness always measured relative to other individuals in same population

Mutations can be deleterious (what does this mean), beneficial (what does this mean), or have no effect (what does this mean)

Mutations can be deleterious (bad), beneficial (good), or have no effect (neutral). 

Adaptation:

 a favored trait that evolves through natural selection

Heritability (h²): def and equation

 is the proportion of total phenotypic  variation in a population due to genetic variation 

VsubG / VsubP

When h2 is close to 1

 then most phenotypic variance due to genetics; trait will not change much within lifetime of individual.

If h2 is near 0,

 then most phenotypic variation due to plasticity, so trait may change within lifetime of individual.

Phenotypic plasticity:

the ability of a single genotype to produce different phenotypes (observable traits) in response to varying environmental conditions

Is evolution and natural selection the same thing?

No! Natural selection can lead to evolution. Evolution ≠ Natural Selection! Evolution is change in the genetic makeup of a population over time. Natural selection is one mechanism by which evolution can occur.

What are the 5 evolutionary processes? 

1. Mutation

2. (Natural) Selection: a non-random process of evolution that favors individuals that survive and reproduce

3. Gene Flow: Migration of individuals or movement of gametes (e.g., pollen) between populations results in gene flow, which can change allele frequencies

4. Genetic Drift: random changes in allele frequencies from one generation to the next

5. Nonrandom mating: a reproductive scenario where individuals choose mates based on specific phenotypes or genotypes rather than pairing randomly, violating Hardy-Weinberg equilibrium

Gene flow:

Migration of individuals or movement of gametes (e.g., pollen) between populations results in gene flow, which can change allele frequencies

Genetic drift:

random changes in allele frequencies from one generation to the next

With no countering forces, any allele  is subject to fixation over time thorugh genetic drift (t/f)

true

Genetic drift tends to eliminate genetic variation. Unless counteracted, drift will result in fixation of a single alleles (t/f)

true

Are large population easily affected by genetic drift like small populations are?

No, Genetic drift doesn’t affect large populations as much.

Genetic drift can cause…

Harmful alleles may increase in frequency, or rare advantageous alleles may be lost (t/f)

true

 Population bottleneck

1. an environmental event results in survival of only a few individuals (ex. Oil spills, forest fires, hurricanes)

when a few individuals from a population colonize a new area and become isolated, genetic drift changes allele frequencies

Founder effect:

when a few individuals (very small population) from a population (large population) colonize a new area and become isolated, genetic drift changes allele frequencies 

(t/f) founder effect Causes loss of genetic diversity and intensifies genetic drift

true