Evolutionary conservation refers to genes, proteins, or biological processes that have remained similar across different species over millions of years. These shared elements point to a common origin and an important function for the conserved element. The persistence of these biological components suggests they perform a function so fundamental to life that changing them is disadvantageous.
When a particular biological feature is preserved across vast evolutionary distances, such as between bacteria and mammals, it signals that this feature is indispensable. The study of these conserved elements provides a window into the most basic requirements for life. It highlights the shared ancestry and the fundamental building blocks that have supported life’s diversity.
The Driving Force Behind Conservation
The primary mechanism responsible for maintaining these sequences is a process known as purifying selection, or negative selection. This evolutionary force removes new, detrimental mutations from a population’s gene pool. When a gene or protein performs a function basic to survival and reproduction, most changes to its sequence are likely to be harmful, impairing its function and reducing the organism’s fitness.
Organisms carrying these harmful mutations are less likely to survive and pass on their genes, so the mutations are purged from the population, preserving the original sequence. The strength of this purifying selection is directly related to the importance of the gene or protein. The more integral a component is to an organism’s life, the stronger the selective pressure will be to keep it unchanged.
Examples of Highly Conserved Elements
Among the most striking examples are genes that orchestrate development. The Hox genes, for instance, determine the basic body plan of an embryo along the head-to-tail axis, ensuring that limbs and organs develop in the correct places. These genes are found in a wide array of animals, from fruit flies to humans, and their function has been maintained for over 500 million years.
Certain proteins for basic cellular operations also show high levels of conservation. Histones are proteins that package and order DNA into nucleosomes, and the structure of histone H3 in a pea and a cow differs by only two amino acids despite diverging over a billion years ago. Another example is cytochrome c, a protein for generating cellular energy, which is nearly identical between humans and chimpanzees.
Entire biological pathways can be conserved. Glycolysis, the metabolic pathway that converts glucose into pyruvate to release energy, is one such process. This sequence of reactions is found in nearly all organisms, from simple bacteria to complex mammals. Its near-universal presence indicates it was an early and important innovation for energy metabolism.
Identifying Conserved Sequences
Scientists identify conserved regions through comparative genomics, which involves comparing the complete genetic blueprints, or genomes, of different species. By examining genomes side-by-side, researchers can pinpoint sequences of DNA or protein maintained across evolutionary time. This process relies on computational methods to analyze the vast amounts of data involved.
A core technique is sequence alignment, which arranges the DNA or protein sequences of two or more species to identify regions of similarity from shared ancestry. The alignment highlights similarities that can indicate a shared functional or structural role. The degree of sequence similarity often correlates with the evolutionary distance between the species.
Scientists use powerful bioinformatics tools for these comparisons, with one of the most widely used being BLAST (Basic Local Alignment Search Tool). BLAST allows researchers to search entire databases of genetic information to find sequences similar to a query sequence. This tool can reveal deep evolutionary relationships and identify conserved domains within proteins.
The Role of Conservation in Scientific Discovery
The study of conserved elements is important for scientific research, particularly in the use of model organisms. Because fundamental biological processes are shared, scientists can investigate organisms like yeast (Saccharomyces cerevisiae), fruit flies (Drosophila melanogaster), and mice (Mus musculus) to gain insights into human biology. These organisms are easier to study in a lab due to their short generation times and established research techniques.
This approach is useful in understanding human diseases. Many genes implicated in conditions such as cancer, diabetes, and neurodegenerative disorders are conserved between humans and these model organisms. For example, studying the genes that regulate cell division in yeast has provided a deep understanding of the cell cycle, and disruptions in this cycle are a hallmark of cancer. This allows researchers to investigate the molecular mechanisms of a disease in a simpler system before applying that knowledge to human health.