29Sept16 – Working through rock pocket mouse activities

List of Activities from Index Page:


Natural Selection and Evolution of Rock Pocket Mouse Populations. (HMMI Biointeractive activity – analyzing data and answering questions)

Color Variation Over Time in Rock Pocket Mouse Populations  (more in same vein – analyzing data and answering questions)

Allele and Phenotype Frequencies in Rock Pocket Mouse Populations – an introduction to Hardy Weinberg

What we did/More information

We started with the two rock pocket mouse activities. First one: Natural Selection and Evolution of Rock Pocket Mouse Populations.

— There’s a short excerpt from Smithsonian (here’s the link to the entire article: http://www.smithsonianmag.com/science-nature/evolution-in-black-and-white-50053448/?no-ist). There’s also a short film that shows two scientists who have been working with these mice in New Mexico for years now – it is only 10 minutes, so well worth watching (direct link: http://media.hhmi.org/biointeractive/interactivevideo/pocketmousequiz/).
— We filled in the amino acids for the different mice populations; we’ll learn lots more about all of this later on in genetics.
— There are also some great questions to answer. Jack answered orally, but will be writing most of these down. The answers might seem simple and obvious, but it is about learning how to use the language of biology when discussing selection, fitness, and so on. The Teacher’s handout has the “answers” so you can check your answers (link to HMMI page: http://www.hhmi.org/biointeractive/natural-selection-and-evolution-rock-pocket-mouse-populations). Question #5 actually confused us, since we weren’t sure exactly what they were looking for.

The question is: If two of the lava flows in New Mexico were near each other and included spans of rocky outcrops between them, what would be a possible mechanism, other than new mutations, to drive the decrease in the light coat-color gene frequency and the increase in the dark coat-color gene frequency in these rock pocket mouse populations? Explain your answer.

— There would be breeding between all the populations, right? Once the mutation has happened, natural selection would keep the frequency of the dark fur gene higher in the mice living on the lava, and vice versa for the light mice on the sand. But that seemed too simple.

The “official” answer is: Gene flow (migration) could be the mechanism in the described scenario. If the lava flows were indeed close to one another, rock pocket mice may be able to migrate from one population to another. Also, if spans of rocky outcrops are between the lava flows, then these habitats would provide suitable locations for migrating dark mice to “hide” in during the migration in order to avoid predators. Gene flow may introduce beneficial alleles into different populations experiencing similar selective pressures.

And that is when we realized we needed to pay more attention to question #4: the other mechanisms. This was a good time for Jack to pull out his textbook, but another alternative that is an excellent source of information on evolution is the Berkeley Paleontology’s website on evolution: http://evolution.berkeley.edu/evolibrary/home.php        Here are some good starting points:

— You should work towards understanding all of the terms on this page: http://evolution.berkeley.edu/evolibrary/article/evo_14
–The starting definition of evolution:
Biological evolution, simply put, is descent with modification. This definition encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history of life.

Second activity: Color Variation Over Time in Rock Pocket Mouse Populations 

–This activity had you look through some pictures depicting rock pocket mice in two locations over time (mixed up). We counted our mice and then put the illustrations in order. One thing that bothered us is that the first picture showing location B BEFORE the lava flow has one dark mouse. This indicates the dark mutation was already present in the population. We don’t think there would have been any selection pressure to keep a dark fur mutation around for there to be any dark mice before the lava flow.
– – If you’d like to see some “official” answers, again, look at the teacher’s handout (see http://www.hhmi.org/biointeractive/color-variation-over-time-rock-pocket-mouse-populations

 

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