# Weekly Response #3

This week in AP Bio, we covered a bunch of things. Starting with the punnett square created by Reginald Punnett, which is pretty much the foundation of the Hardy-Weinberg law. We have been using the punnett square since 8th grade so that was never a problem, but what the punnett square is really helpful with is seeing how and why the Hardy-Weinberg equation works.

In the Hardy-Weinberg equation, p is dominant and q is recessive. The first part of the equation (p^2) comes from the upper left box, where we can see the two dominant traits have come together to be homozygous dominant. The 2pq in the equation comes from the two boxes where one dominant and one recessive allele have come together to be heterozygous dominant. Lastly, the q^2 in the equation comes from the two recessive alleles coming together to be homozygous recessive. What we see here on the punnet square is called the genotype (the actual genetic makeup), what we would actually see is known as the phenotype. When looking at a punnett square, to visualize the phenotype you just have to know that the dominant trait is the one that will always show, the only time that we would see the recessive trait appear is when there is no dominant trait so it has to be homozygous recessive (only in the q^2). At first glance, the Hardy-Weinberg equation is pretty intimidating, but once you know how it works and can visualize it , it becomes pretty easy.

Another thing that we started learning about this week was phylogenetic trees, we didn’t cover it much in class but we did learn about it through a packet and an online presentation. My main take from this so far is that the trees are used to show how closely related organisms are, the closer they are to each other on the line, the more closely related they are. These trees can also show a common ancestor, at the root shows the most recent common ancestor for the organisms above it.

These trees can be helpful to show what organisms are and aren’t related to other organisms as well as how closely related the organisms actually are. Most of this is done by the alignment of DNA sequences making it extremely accurate.  DNA doesn’t lie, for example: In the small clip we watched for homework, we could see that the hippopotamus is more closely related to a whale than it is to a pig. Based off of simple anatomical features, most people would not have guessed that, but based off of the DNA, we could see that they were very closely related, despite showing hardly anything obvious in common.

One other thing that we covered was mutation, most of evolution occurs by mutations, often mutations that are beneficial to the organism in it’s environment. The two main types of mutation are SNP’s and Indels. An SNP is when one DNA base pair changes to another.

The mutations known as indels are insertions and deletions in the genetic code. Both of these mutations can be picked up pretty easily by computers.