This week in AP-Bio, we continued to practice using the Hardy-Weinberg equations and we continued to work with cladograms. I am not really sure how much new stuff we covered this week, it seemed like it was all stuff that we started last week, only more in depth.
We covered how to properly make cladograms, which so far has been pretty straight forward, but will most likely get very difficult down the road. The first thing that I do when making a cladogram is find the two organisms that are the least related genetically. If you find the two that are least related, you can start the cladogram with one of those organisms (the least evolved or least complicated should be at the bottom) and the other should be at the top (the most evolved, often most traits acquired). From there, I would work bottom up. Find the organism most related to the one at the bottom, the one that is most related genetically will be the next organism on the graph. This continues until it reaches the top. If this is done properly, you should be able to write the traits below as they are acquired, and most of the time, that trait will continue through the rest of the organisms on the cladogram.
At first, it was hard for me to understand how this all worked. When I was watching the video for the Bio homework last week, they mentioned how you can rotate parts of the tree at each common ancestor and it will still give the same results. My issue with understanding how that works is that I thought how close the organisms were to each other at the top showed how related they are, but that is not exactly true. When comparing organisms the first place to look should not be at the organism itself, but at the most common shared ancestors of the organisms. For example if you look at the cladogram above, you will see that the organisms are ordered: Sharks, ray finned fish, amphibians, primates, rodents and rabbits, crocodiles, birds. Based on the fact that you can rotate the tree at ancestors, you could rotate it so that birds were the organism closest to amphibians, so it may not always be primates in that spot.
In class we covered a common mistake made by students. The idea of drift got passed around as “the chance of genes being passed on.” Many students (including myself) were under the impression that drift was like a human stepping on a group of green bugs, and because of that, only the brown bugs would pass along their genes. We concluded therefore that drift was completely random, but that’s not really true.
We covered a topic in class that was made interesting thanks to the silver fox. We covered selective breeding, we learned about it through a screwed up Russian guy named Belyaev. He was a man who wanted to pretty much take the sport out of hunting and make it easy slaughter instead. What was happening at this time was people would kill the foxes and sell the fur (which is pretty cool fur not going to lie), but this man was tired of the foxes biting and attacking the people who were hunting them. So instead of making bite proof pads or something, he decided to just breed the fight out of them. To do this he took the nicest/most curious foxes and bred those together while just killing the mean ones. We found that this did work, the breeds later on were way nicer then the original ones, but something that was not predicted happened. The foxes began to develop new traits such as shorter tails, floppy ears, and change in color pattern. What Belyaev found was that the trait for niceness, was linked to many other traits as well, by altering one trait, he altered many. This gives us an idea of why dogs came to look so different from wolves, and why there is such a huge variety, it’s because when you breed for one trait, you often alter many.