From previous chapters, students have already obtained the sequences of the genes and proteins related to their aoi. In order to obtain more information about these genes/proteins, such as their evolutionary relationships, it is useful to obtain the gene/protein sequences of related genes/proteins. This is important because the conserved regions of homologs are closely related to the structure and function of the molecules. To determine if genes are homologous, we need to determine if their sequences are more similar then we would expect them to be by chance. When we compare two sequences, we measure how similar/different the sequences are. Our conclusions about whether the genes/proteins are homologous are drawn based on hypothesis testing. We propose the null hypothesis that these sequences are random vs the alternative hypothesis that these sequences are related. Therefore, it is important the statistical background of sequence comparison. Normal distributions are often used in statistical analyses, however, for sequence comparison, it follows an extreme value distribution (EVD), which we will learn in this lab.