Chapter 17, Problem 10STP

Summary Introduction

To assess:

The ways in which molecular clocks are more useful in investigating phylogeny than morphological characteristics.

Introduction:

Scientists believe that species sharing a common ancestor also share an evolutionary history. The evolutionary history of an organism is called its phylogeny. A system of classification that shows an evolutionary history of an organism is a phylogenetic classification and it reveals the evolutionary relationships of species.

Answer to Problem 10STP

Molecular clocks are more useful in investigating phylogeny than morphological characteristics as they are more reliable and accurate. Molecular clocks are used to compare DNA sequences or amino acid sequences of genes that are shared by different species. Using morphological characters to find out if the species are closely related or not and evolved from common ancestor is not very accurate.

Explanation of Solution

A molecular clock is a model that is used by systematics to compare DNA sequences from two different species to estimate how long the species have been evolving since they diverged from a common ancestor. Biologists use molecular clocks to compare DNA sequences or amino acid sequences of genes that are shared by different species. The differences between the genes indicate the presence of mutations. The more mutations that have accumulated, the more time has passed since divergence. Researchers try to compare genes that accumulate mutations at a relatively constant rate in a wide variety of organisms. For example the gene for cytochrome c, found to be present in mitochondrial DNA of most organisms, show similar rates of evolution in different organisms.

Characters are inherited features that vary among species. They can be morphological or biochemical. Based on shared characters, scientists construct patterns of descent or phylogenies.Shared morphological characters suggest that the species are closely related and evolved from common ancestor. However analogous characters do not indicate close phylogeny.