natural selection

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Darwin’s theory of Natural Selection

theory that states competition for limited resources results in differential survival

Fitness

________ is measured by reproductive success

phenotypic variations

natural selection acts upon this; significantly increase or decrease fitness of organisms in particular environments

selective pressures

what happens when environmental conditions change and are applied to populations

Fluctuation of botic & abiotic environments

affects the rate and direction of evolution, and so different genetic variation can be selected in each generation

Artificial Selection / selective breeding

people choosing which traits they liked and breeding those organisms; concludes that species could change over time.

populations

evolve over time

heritable traits

Natural selection can only increase or decrease ______ ____ that vary in a population 

descent with modification

helpful adaptations (inherited traits that increase survival & reproduction) will increase in the species, and the non-helpful traits will decrease, leading to change in populations over generations

mutation and sexual reproduction

Genetic diversity in a population comes from 2 main mechanisms

mutations

ultimate sources of new alleles, or new genetic variation, which provides phenotypes on which natural selection acts; can increase, decrease, or have no effect on fitness

sexual reproduction

provides unique combinations of alleles through crossing over, independent assortment, and fertilization 

duplication of genes

can take on new function by further mutation, which likely played a major role in evolution

prokaryotes

Mutations in _________ are slow, but they reproduce rapidly, allowing mutations to accumulate rapidly

viruses

Mutation rates are faster in ______ because their RNA can’t be repaired by host cells and they also reproduce quickly

Population genetics

measures change in a population’s allele frequencies over time

gene pool

all of the alleles in a population

Hardy-Weinberg equilibrium

a stable non-evolving state

evolving

if a phenotype is favored by natural selection, allele frequencies can change, which means the population is

evolved

if there has been a change in allele frequencies in the population over generations, by definition of microevolution, the population has

alleles, genotypes

If a population is in Hardy-Weinberg equilibrium, the frequency of _____ and ______ in that population will stay the same over generations

no mutations, random mating, no gene flow, very large population, and no natural selection

In order for a population to be at Hardy-Weinberg equilibrium, a non-evolving state, all 5 conditions must be met:

genetic drift

random change in the frequency of allele due to a chance event; can occur in any population, even very large populations, but it has a stronger effect on small populations

bottleneck effect

in a large portion of the genome being wiped out and the allele frequency is determined by the survivors, which may be very different from the pre-disaster population

The founder effect

where a small portion of the population leaves & starts a new population in a new location; the founding individuals may not represent the full genetic diversity of the original population

adaptive evolution

increases the frequency of the helpful alleles from one generation to the next

Stabilizing Selection

eliminates the extreme ends of a trait and favors the average expression of a trait

Directional Selection

When an extreme version of a trait is more fit and selected

Disruptive Selection

A population gets split into 2 groups and removes individuals with average traits

Sexual Selection

the ability to attract a mate