Classical Genetics and Evolution
Question 1: Compare and contrast macroevolution and microevolution.
Answer 1: Macroevolution may be defined as the major phenotypic changes that occur over long periods of time and that finally result in a new taxonomic level above species. Macroevolutionary affects include major changes in anatomy and physiology and basic changes in body design. An example of such a change is the evolution of stomata and cell guards in plants that allowed them to regulate gas exchange. In animals, an example would be the evolution of the reptilian foreleg into the wing of a bird. In general, macroevolution causes major changes in the appearance and functions of plants and animals and results in new taxonomic levels of a high order.By contrast, microevolution works on a much smaller scale. Microevolution refers to small-scale changes in gene frequencies that generate new species, rather than a higher taxonomic order.
There are lots of good resources about Evolution that you can find available.
Question 2: Define fossil and discuss the problems of using them as a tool in tracing evolution.
Answer 2: Fossils are the hardened body parts of plants and animals which remain after an organism dies. They include bone, shells, and impressions made in soft sediment. Fossil evidence may be used to track some lines of descent very well, but many lineages are difficult to trace using fossils. Fossil evidence is an incomplete record of the earth’s evolution of life, but it provides a great deal of information that can be useful in the study of evolution.Problems with fossils as a tool in tracing evolution are the following:1. The majority of organisms that ever lived left no fossils.2. Only a tiny percentage of organisms with hard parts would have been preserved as fossils.3. Fossils that did form were often altered or destroyed by geologic changes of the earth or by chemical reactions which dissolved them.Although fossils provide a window into the process of evolution, they provide only a partial picture at best.
Question 3: Define radioisotope dating and discuss its use.
Answer 3: The most accurate method of determining the age of fossils is radioisotope dating. In this method, radioactive isotopes are used as biological clocks for measuring time. To use radioisotopes effectively in fossil dating, the scientist must know the isotope’s half-life: the amount of time it takes for one half of the isotope to decay. The scientist must first determine how much of the isotope was originally present in the fossil and then how much of the isotope is left. When all these factors are known, a scientist can calculate the age of the fossil with about 98 percent accuracy. The older the fossil, the longer the half-life of the isotope must be to accurately date the fossil. Uranium-235, with a half-life of 713 million years, or uranium-238, with a half-life of 4.5 billion years, are both very useful in dating more ancient fossils. Isotopes with shorter half-lives may be used to date relatively recent fossils.
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