Variation in a Population and Mechanisms of Evolution

Flashcards covering the variation in populations, types of natural selection, mechanisms of evolution, and patterns of speciation based on lecture notes.

What are the three main types of selection pressures identified in the lecture?

Directional Selection, Disruptive Selection, and Stabilizing Selection.

In the beetle population example, why did the brown trait become more common?

Because green beetles were eaten by birds and survived to reproduce less often than brown beetles, the brown coloration provided a reproductive advantage based on heredity.

List four factors that influence Differential Reproductive Success (DRS).

Competition, Limited resources, Producing more offspring than can survive, Environmental factors, Viability, Fecundity, and Genetic Variation.

Define Directional Selection.

A process of natural selection in which a single phenotype at one extreme of the phenotypic range is favored, causing the trait distribution to shift toward that extreme.

What is Disruptive Selection and what can it lead to?

A process of natural selection that favors individuals at both extremes of a phenotypic range; it can cause differences that lead to new species ($SPECIATION$).

Define Stabilizing Selection.

A process of natural selection that favors genotypic combinations producing an intermediate phenotype, reduces phenotypic variation, and maintains the status quo.

Provide examples for Directional Selection.

Neck of Giraffe, antibiotic resistance of bacteria, moth color ($melanin$), and camouflage/mimicry.

Provide examples for Stabilizing Selection.

Bird clutch size, human birth weight, and human height.

What are the primary mechanisms of evolution described in the notes?

Natural Selection, Mutations, Gene flow, Genetic drift, Artificial selection, and Non-random mating.

What is Gene Flow?

The movement of genetic information (traits) between populations, allowing new genetic information to enter the gene pool.

What is Genetic Drift and what population size does it primarily affect?

The change in frequency of an existing gene due to random chance, which mainly affects small populations and is often caused by natural disasters.

Contrast Divergent and Convergent evolution in terms of structures.

Divergent evolution leads to descendants with homologous structures from a common ancestor, while Convergent evolution involves analogous structures in species with different ancestors but similar ecological roles.

What is Parallel Evolution?

The independent evolution of similar traits in species that once shared a similar ancestor and are exposed to similar selection pressures but are geographically isolated.

Define Coevolution and give a common example.

Coevolution is when two or more species reciprocally affect each other's evolution, such as in predator/prey relationships.

Define Allopatric Speciation and name one geographic barrier mentioned.

Speciation that results when two populations become isolated by a geographic barrier, such as rivers changing course, mountains forming, or continental drift.

What are sympatric species?

Closely related but reproductively isolated species living in the same or similar geographic range.

What is Parapatric Speciation?

Speciation occurring when two subpopulations evolve reproductive isolation due to habitat differences within a population range, with no specific extrinsic geographic barrier.

How does Sympatric Speciation most commonly occur in plants?

Through $polyploidy$, which is when offspring have more than the normal number of chromosomes due to the failure of chromosomes to separate during meiosis.

Define Parthenogenesis.

Reproduction from an ovum without fertilisation in animals, which can lead to a decrease in genetic variability and rapid divergence of characteristics.

What is Character Displacement?

A form of sympatric speciation where selection pressure for resource partitioning results in different gene pools, as seen in the Galapagos finches.