Topic 1C: Evolution

Topic 1C: Evolution

1. Microevolution: genetic changes within a population

   • competitive interactions within the population are key to natural selection and to overall microevolution of the population, as ability to compete for resources can influence fitness and reproductive success

2. Macroevolution: changes that occur to a species on a larger scale over a longer period of time

   • Speciation
     • allopatric: members of the same species evolve differently from each other after geographic isolation, to point they cannot mate with each other (the definition of a species)
     • sympatric: nongeographic barriers prevent 2 members of the same species from mating with each other, resulting in a new species
     • when mechanisms preventing interbreeding fail, this may result in hybrid species
       • prezygotic isolation: prevent fertilization between the gametes of members of two different species
         • temporal isolation: the 2 species have different breeding seasons or times
         • ecological isolation: the 2 species may live in different habitats
         • behavioral isolation: noncompatible mating behaviors
         • gametic isolation: copulation occurs, but the gametes are not able to fertilize each other
         • reproductive isolation: noncompatible reproductive structures
       • postzygotic isolation: mechanisms that occur after fertilization to prevent interbreeding
         • Hybrid inviability: zygote is not able to develop
         • Hybrid sterility: hybrid offspring is unable to reproduce
         • Hybrid breakdown: hybrid is able to reproduce, but 2nd generation is infertile
       • by definition, a species is made up of individuals that can reproduce fertile, viable offspring. This is why hybrids are considered infertile, because either they or their offspring are infertile or not viable; otherwise they would form a new species and not be called hybrids.
     • events that may impact genetic diversity of a species: inbreeding (mating of closely related members of the species, decreases the genetic diversity in the population, and increases the frequency of harmful diseases), outbreeding (increases genetic diversity, opposite of inbreeding, increases reproductive fitness), and genetic drift.

3. Mechanisms of Evolution:

   • mutations (new alleles can provide new advantages that maybe selected for, or disadvantages that are selected against)
   • natural selection: explains the increase in frequency of favorable alleles from one generation to the next. Differential reproductive success (certain individuals reproduce more than others, resulting in their traits being "selected for" and resulting in increase in those alleles in the population
     • evolutionary fitness (measure of reproductive success and contribution of alleles in the next generation) is key to natural selection. Individuals who are more fit are more evolutionarily successful because their genetic traits are passed to the next generation, thus increasing the frequency of specific alleles in the gene pool.
       • adaptation: genetic changes in the population as a result of changes in selective pressures; can lead to increased or decreased fitness/change in who or what is considered "fit"
     • disruptive selection: a type of selection where both of the extreme phenotypes are selected for and the intermediate is selected against. Over time, this can lead to the development of 2 distinct species
     • stabilizing selection: favoring the alleles that produce an intermediate phenotype. Ex: human birth weights
     • directional selection: a type of selection where 1 extreme phenotype is preferred and the other phenotypes are selected against. Ex: abx resistance in bacteria; over time the entire population ends up with the same allele, until selective pressures (the abx) change
     • artificial selection: particular alleles are purposely selected for based on nonrandom mating; traits that are artificially selected for are not necessarily the result of the most fit alleles. Ex: dog breeding
     • 3 guiding principles: variation (individuals in the population will have different traits), inheritance (traits will be passed on from generation to generation), and competition (due to limited resources, only a certain amount of offspring will be able to survive and those will be the ones with traits suited to the environment).
     • group selection: the idea that natural selection can act on groups, selecting some over others, resulting in traits that our advantageous in groups.
     • alleles, in their increase in the gene pool, can be a measure of evolutionary success
   • Gene flow: migration of individuals in a population, results in changes gene pool as alleles enter or leave the population. Can also be the flow of genes from one species to another (Ex: one species of a deer mates easily with another, leading to formation of hybrids in the population)
   • Genetic Drift: changes to the allelic frequencies within a population due to chance, generally negligible in large populations, but major consequences possible in smaller populations
     • Bottleneck: form of drift where catastrophe wipes out a portion of the population, resulting in the remaining portion of population not being representative of the prior
     • Founder Effect: a small number of individuals leave a larger population and form their own small population where inbreeding is necessary. The new population only has the diversity brought to it by the founding members
     • describes the change in frequency of alleles due to events that influence reproduction in the population; generally occurs in the absence of selection pressures, and with random sampling.

4. Symbiotic relationships between species: two species exist together for extended periods of time

   • Parasitic: one species benefits, the other is harmed
   • Commensal: one species benefits, the other is unaffected
   • Mutualistic: both species benefit from the association

5. Hardy-Weinberg Equation

   • used to calculate allelic frequencies within a population that meets certain criteria; this is the theoretical, actual populations usually do not meet these conditions
     • 1} large population (no genetic drift)
     • 2} no migration/gene flow
     • 3} random mating
     • 4} no mutations
     • 5} no natural selection
   • p^2 + 2pq + q^2 = 1
   • p + q = 1
   • assumes genotype and allele frequencies do not change over generations. Equilibrium is achieved when gene frequencies do not change over time (i.e., the population does not evolve).

6. Convergent Evolution: a type of evolution where 2 populations in similar environments and under the same selective pressures evolve in a similar manner. Ex: analogous structures (ex: fish in the Arctic vs fish in Antarctica developing the same glycoproteins to protect their tissues in the cold; the fish are on opposite sides of the world and are genetically different from each other, yet have these similar structures d/t similar evolutionary pressures)

7. Divergent Evolution: a type of evolution where individuals in the population evolve differently from each other. Over time, they may become different species. Ex: homologous structures (vertebrate arms are of the same origin, but have different forms and functions)

8. Parallel/Co- Evolution: a type of evolution where the evolution of one species can affect the evolution of the other species. Ex: predation patterns of birds impacting the evolution of butterflies, and how some of the butterflies will be poisonous while others will just mimic the colors of the poisonous ones

9. gene pool: the sum of all the alleles in the population that can combine to pass on genes to the next generation.

10. molecular clock: genetic drift, abiotic factors (change in environment, fossils, etc), and rate of mutation can be used to determine a timeline of when a species diverged.

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