Round-up: Darwin, Evolution and More!

This past unit has been a busy one for the AP Bio Team, as we covered chapters on Darwin, evolutionary theories, and even some math that goes along with the evolution of populations. We started off by covering the various theories of evolution and Darwin’s contributions that claimed organisms change and adapt, like the finches he researched. We watched various clips that discussed the Galapagos Islands and Darwin’s observations on the islands. There were also a couple of in-class discussions about these theories and Darwin’s journey around the world. These class discussions brought up a lot of good points about the way evolution was viewed has changed a lot over time and that Darwin’s journey was a pivotal change for how we view evolution. After various classes of watching videos and discussion, we moved on to the evolution of populations and the Hardy Weinberg equation.

Darwin's finches

We first discussed the ideas that populations have variations of alleles, or different versions of a gene, the frequency of these alleles can be determined and that allele frequencies change due to various factors such as natural selection, genetic drift and gene flow. Allele frequencies can be calculated using the Hardy Weinberg equation:
p² + 2pq + q² = 1
Initially this equation doesn’t look too inviting, however it is quite simple. “p²” stands for the frequency of homozygous dominant alleles in the population, “2pq” is the frequency of heterozygous alleles and you can probably guess that “q²” stands for the frequency of homozygous recessive alleles. This equation can be used to predict and describe what alleles and their frequency are in the population. 

Along with learning about the Hardy Weinberg equation, we discussed the five conditions that must be met for a population to stay the same and have no alterations in frequencies. These five conditions are:
Large population, random mating, no mutations, no movement, no natural selection

As you can probably assume, these conditions are not met in real life, however, it just shows the environment needed to have no changes in population. Also, as a class, we conducted a lab that involved the class “randomly mating,” using cards with “A” and “a” as different alleles, for five "generations," or rounds of mating, under various conditions. We counted how many people had each type of allele at the end and then calculated the before and after allele frequencies to practice using the Hardy Weinberg equation. It was a very fun and interactive lab that was enjoyed by everyone. 

After reviewing Hardy Weinberg, we then moved on to a virtual lab that looked at the evolution of Stickleback fishes. Each student went through the lab online, looking at how scientists identify differences in a Stickleback population by looking at the pelvic spines of living fish from various lakes and various fossils of Stickleback fish. These spines are present in some Stickleback populations, while other populations have very few individuals with a spine. This lab showed how the presence of the Stickleback spine in certain areas decreased over time due to their environment. Which means this lab demonstrated how an organism can adapt and change, or evolve, over time to suit the environment better. The Stickleback lab also introduced the idea of Chi-Square analysis, which is a statistical test done to determine the likelihood that the data is accurate and reliable. This statistical analysis is difficult to explain, but very useful in labs and experiments once understood.

Stickleback fish with and without pelvic spines 

Overall, this unit was very interesting, as it looked at the broader picture of life and evolution. The various in class activities and labs we did helped our understanding and I’m looking forward to see what we’re learning next! Thanks for reading!

Works Cited:
Gould, John. Darwin's Finches. Digital image. Wikimedia. Wikimedia, 27 Feb. 2012. Web. 15 Feb. 2015. <http://commons.wikimedia.org/wiki/File:Darwin%27s_finches_by_Gould.jpg>.

Shapiro. Convergent Pelvic Loss. Digital image. Shapiro Laboratory. University of Utah, n.d. Web. 15 Feb. 2015. <http://biologylabs.utah.edu/shapiro/Shapiro_Lab/Research.html>.