Study Guide

Mechanisms of Evolution - Common Mistakes

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Common Mistakes

Charles Darwin and the Origin of the Species

  1. Remember that a genotype represents an organism's genes, while a phenotype is a physical characteristic.
  2. Multiple genes can affect one phenotype (polygenic). Multiple alleles can exist for one gene.

The Gene Pool

The Hardy-Weinberg equation uses allele frequencies (the likelihood a gamete will have a specific allele) to calculate the percent of genotypes (two alleles in the diploid) in the population. When does Hardy-Weinberg principle apply? Well, only when there is no evolution. Therefore, using this equation to assess allele frequency tells us if a mechanism of evolution is acting on the population.


Just remember that although mutations are thought of as malicious and evil, they often do nothing. Sometimes, they give a cool advantage to an individual. It all depends on where the mutation is located and whether it changes an important protein. That said, we're not suggesting you skip the sunscreen. Or crawl through a sewer.

Gene Flow and Genetic Drift

The bottleneck effect—envision an old school coke bottle. It has a small neck. If you were to fill it with marbles, shake it up, and turn it upside down, only a few marbles can escape at a time. Maybe only the amount of marbles that make it out within two seconds are the ones that survive. It's the same idea with a population, just without the marbles. With the founder effect, think of a new population being "founded" from just a few marbles.

Sexual Selection

Intrasexual vs. Intersexual: Intra comes from the latin for inside/within. This is sexual selection within the same sex (like male vs. male). Inter for the latin for among. This is sexual selection among a species (like male vs. female).

Natural Selection

You can use the names of the selection to help visualize what the second-generation graph would look like. Stabilizing selection will stabilize the graph and keep a similar shape. Directional selection will push the bell curve in one direction or another. Disruptive selection will totally disrupt the bell curve, creating a new bimodal shape.


Allopatric comes from the root words for "other" and "homeland," while sympatric comes from the root words for "same" and "homeland." This helps describe the main difference between them. Allopatric speciation occurs when one population is in one place and a second population is in another. Sympatric speciation occurs even when the two diverged species live in the same location.

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