Biological evolution, simply put, "is change through time" says Robert Jansen, UT professor and chair of Integrative Biology.
Variation among organisms in nature is clear, Jansen said. Changes that occur in an environment cause some of these organisms to be better suited to the change than other organisms because of this variation. The traits that allow some organisms to better adapt will persist through time via those better adapted organisms.
The more poorly adapted organisms will not survive, and, as a result, their traits will be lost. This process that causes evolution to occur is called natural selection.
The material that allows traits to be passed on from one generation to the next is deoxyribonucleic acid, or DNA.
Jansen's research at UT concentrates on the evolution of DNA that is contained in the chloroplasts of plant cells. Chloroplasts are the part of a plant cell where light energy is converted into chemical energy the plant can use to grow and survive. The DNA in chloroplasts is unique, Jansen said, because it is only inherited from the female plant. This is different from the DNA located in the nucleus, another place where DNA is found cells, which is inherited from both parents.
By carefully analyzing the DNA, Jansen can determine the sequence in which the fundamental units of DNA occur. It is this sequence of the DNA in all parts of the cell that ultimately determines which traits an organism will have.
This sequence is normally passed from one generation to the next without change. Sometimes, however, the DNA sequence can change for a variety of reasons, such as damage from UV light. A change in the sequence is called a mutation, Jansen said, and mutation is the source of variation. If a variation can be passed to the next generation, it causes evolution to occur.
By recording the sequence of DNA from a plant, Jansen said he can determine some of the traits that plant possesses. By looking at different recorded sequences of DNA from different plants, he can compare the similarities of traits. These comparisons are made by loading the recorded DNA sequences into powerful computer programs that can resolve how different two plants are from each other. Jansen noted that many of these programs used to make comparisons, called algorithms, are created at UT. The closer the similarities in DNA sequences, the more closely two organisms are related. Using a large data pool, Jansen can create a phylogenetic tree that shows how closely two organisms are related to one another and can show relatively how far in the past two organisms began to differ from one another.
The research Jansen performs on the evolution of chloroplast DNA has many direct practical and important applications. Pharmaceutical companies can use these phylogenetic trees to discover plants of medicinal importance based on the closeness of their relation to established medicinal plants, Jansen said. These trees can also be used to find close wild relatives of domesticated food crops to help protect against pestilence.
The information Jansen gathers concerning the nature of chloroplast DNA helps lead to environmentally safer, genetically engineered crops. Recall that chloroplast DNA can only be passed on from the female plant, the plant that produces the seeds; therefore, genetically modified DNA cannot be passed on by pollen from a genetically engineered crop to a closely related and receptive wild crop.
This greatly reduces, if not completely eliminates, the likelihood of contamination of wild plant populations, Jansen said.
Another researcher on campus also utilizes evolutionary theory and creates phylogenetic trees to determine the relatedness of a very different type of plant.
Edward Theriot, director of The Texas Natural Science Center and a professor of integrative biology, studies the evolution of diatoms. These single-celled plants are anywhere from two micrometers to millimeters in length and coat themselves in a thin layer of silicon, Theriot said. Diatoms are used in many everyday products, including wall paint and water filters. Diatoms are even used like liquid sandpaper in toothpaste to clean teeth. Diatoms are also amazingly sensitive indicators of the acidity of water, Theriot said, and they can thus be used as an indicator of the level of pollution in a water-based ecosystem.
Theriot pointed out that "evolution is no more or less a theory than the theory of gravity." He added that "a theory is some concept or idea that has been examined and tested through time, such that it has been very well-corroborated and also has predictive power."
Whereas a hypothesis is "a prediction that has not yet undergone very much examination or testing," Theriot said. Using the predictive power of evolutionary theory, Theriot hypothesized that a diatom, which only occurs in Yellowstone Lake, actually evolved in the lake.
He also hypothesized from which ancestral diatom it evolved. Theriot was later able to prove his proposed evolutionary pathway to be correct by comparing his prediction to the fossil record from Yellowstone Lake that is uniquely complete.
Further information on evolution and how it affects all organisms may be found at the Texas Memorial Museum in an exhibit called "Exploring Evolution" on the fourth floor managed by Christina Cid and Sarah Grice.
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