Chapter 23 - Distances in Biology

Abstract

This chapter focuses on the concepts of distances in biology. The distances are mainly used in biology in order to reconstruct the evolutionary history of organisms in the form of phylogenetic trees. In the classical approach, those distances were based on the comparative morphology and physiology. The modern molecular biology compares DNA/protein sequences between organisms. DNA is a sequence of nucleotides (or nuclei acids) A, T, G, and C, and it can be seen as a word over this alphabet of 4 letters. The nucleotides A, G (short for adenine a guanine) are called purines, while T, C (short for thymine and cytosine) are called pyrimidines (in RNA, it is uracil U instead of T). Two strands of DNA are held together (in the form of a double helix) by weak hydrogen bonds between corresponding nucleotides (necessarily, a purine and a pyrimidine) in the strands alignment. Those pairs are called base pairs. The chapter further elaborates concepts related to genetic distances for gene-frequency data, distances for DNA data, distances for protein data, and other biological distances.