Common Descent has become a conceptual backbone for biology. The idea has supporting evidence in comparative anatomy, embryology, biogeography and now molecular biology. Modern research techniques now allow biologists to compare the DNA that codes for certain proteins in order to make predictions about the relatedness of the organisms.

Genes are made of DNA and are inherited from parent to offspring. Some DNA sequences code for mRNA, which in turn, codes for the amino acid sequence of proteins. Cytochrome C is a protein involved in using energy in the cell and is found in most, if not all. known eukaryotes ( an organism whose cells contain a nucleus and other structures (organelles) enclosed within membranes). Over time, random mutations in the DNA sequence occurs, changing the amino acid sequence of Cytochrome C. Cells without usable Cytochrome C are unlikely to survive.

We manually counted the differences between the sequences ( please make way for human error) of animals, humans and yeast. We counted the differences in amino acid sequences because changes in DNA lead to changes in RNA, which lead to differences in the protein amino acid sequences. Fewer DNA mutations occur in shorter time sequences. This means that more differences in amino acid sequences of Cytochrome C means that the two compared species have a distant common ancestor. Likewise, the less differences in amino acid sequences of Cytochrome C means that the two compared species have a closer common ancestor. Closely

There are other things we can use to determine how organisms are closely related to each other:

1. Vestigial Structures
2. Embryology
3. Paleontological Evidence

Rachel Putri Utomo
Block F, Honors Biology
Mr. Kevin Quick
Academic Year 2013-2014