Molecular Biology and Biodiversity

Molecular biology is primarily concerned with the study of the structure, function, and comparative composition of the molecules of inheritance DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). All organisms have RNA in some form, while only some bacteria lack DNA. In general, the information stored in DNA is "translated" by RNA to govern the construction of protein molecules vital to the differentiation, growth, and maintenance of an organism's body. In eukaryotic organisms (those with a cell nucleus—which includes all organisms except bacteria), DNA is found in the chromosomes of the cell nucleus and also in the cellular organelles outside the nucleus that are concerned with energy production— for example, the mitochondria of animals and the plastids of plants.

Molecular data are being used to identify patterns of genetic diversity among endangered and threatened species. Moreover, very little is known about the genealogical (that is, evolutionary) relationships of a large number of species. Researchers use DNA sequence data to unravel the evolutionary relationships of species. Analyses of this tremendous amount

A researcher works in a molecular biology lab at the California Institute of Technology. Molecular data can be used to identify patterns of genetic diversity among endangered and threatened species, which could lead to a better understanding of evolution, geographic distribution, and other life characteristics. (Vince Streano/Corbis)

A researcher works in a molecular biology lab at the California Institute of Technology. Molecular data can be used to identify patterns of genetic diversity among endangered and threatened species, which could lead to a better understanding of evolution, geographic distribution, and other life characteristics. (Vince Streano/Corbis)

of data will allow us to better understand evolution, ecology, behavior, geographic distribution, and other life characteristics.

Research performed in the molecular biology laboratories has shown that a large number of species have low genetic variation caused by a reduced population size. Thus they are very prone to succumb to global climatic change and environmental degradation. To optimize the chances of species conservation, population size must be maximized, because a large number of individuals have a greater diversity of phenotypes, on account of their genetic variability, than does a smaller group. Thus the most important parameter is the inheritable variation within and between populations of organisms that resides in the variations of the sequence of the four base-pairs (adenine, thymine, guanine, and cytosine in DNA, and adenine, uracil, guanine, and cytosine in RNA), which, as components of the nucleic acids, constitute the genetic material. It is important to determine to what extent reduction of these populations has affected variability.

To understand how such changes could influence the origin of species, researchers are using protein electrophoresis and DNA sequencing to discover and catalogue existing species and to elucidate their evolutionary relationships. Only a small fraction (often less than 1 percent) of the genetic material of higher organisms is phenotypically expressed in the form and function of each cell of an organism; the purpose of the remaining DNA and the significance of any variation within it is still unclear. Genes that control funda mental biochemical processes are strongly conserved across different taxa and generally show little variation, although such variation that does exist may exert a strong effect on the viability of the organism. The opposite is true for other genes, An interesting example is the astonishing amount of molecular variation in the mammalian immune system, which is based on a small number of inherited genes.

New genetic variation arises in individuals by mutations (base substitution, deletion, duplication) in their genes and chromosomes. In organisms with sexual reproduction, mutations can spread through the population by recombination. Other kinds of genetic diversity can be identified at all levels of organization, including the amount of DNA per cell, and chromosome structure and number.

This pool of genetic variation present within an interbreeding population is constrained by selection. The ability to survive results in changes of the frequency of genes among this pool, and this is equivalent to evolution of the population. The significance of genetic variation is thus clear: it enables both natural evolutionary change and artificial selective breeding to occur.

With the aid of mitochondrial DNA (the DNA found outside the cell nucleus in the organelles called mitochondria), polymerase chain reaction techniques, and microsatellite DNA analysis, molecular geneticists and biologists try to determine what characterizes a species and to quantify how close or distant, genetically, species are. Furthermore, these techniques will help to determine whether the DNA within individuals of the same species is adequately diverse to survive drastic environmental changes.

—Amalia Porta

See also: Conservation Biology; Evolution; Evolutionary Genetics; Five Kingdoms of Nature; Natural Selection

Bibliography

Hodder, K. 2001. "What in Earth? Analysing Soil Bacterial Communities." Biologist 48, no. 1:27-29; Ran-jard L., F. Poly, and S. Nazaret. 2000. "Monitoring Complex Bacterial Communities Using Culture-Independent Molecular Techniques: Application to Soil Environment." Research in Microbiology 151, no. 3:167-177; Theron, J. and T. E. Cloete. 2000. "Molecular Techniques for Determining Microbial Diversity and Community Structure in Natural Environments." Critical Reviews in Microbiology 26, no. 1: 37-57.

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