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EVOLUTION AND BIODIVERSITY BIODIVERSITY is the variety of living species on earth. Approximately 1.5 million of the earth's species have been cataloged and described in a scientific paper (i.e., given a scientific name, and been physically described in a refereed journal). A biologist who names and classifies living things is known as a TAXONOMIST. A biologist who studies the evolutionary relationships between living organisms is a BIOSYSTEMATIST. (Most biosystematists are also taxonomists.) Holotype: the very first specimen of a species ever collected and scientifically described. It is on this specimen that the entire species' description is based. Paratypes: the unlucky conspecifics popped into the same jar as the holotype, but they get second billing. (A conspecific is a member of the same species. For example, all the Homo sapiens in this classroom are conspecifics. Just How Much Diversity are We Talking About Here? V Edward O. Wilson (eminent natural historian and philosopher) has estimated that there may be anywhere from 5 - 50 million species on earth. Others have suggested there may be far more. Species: a population or series of populations within which free gene flow occurs under natural conditions. (i.e. - a group of similar organisms which can interbreed to produce fertile, viable offspring under natural conditions). At last estimate, the average mammal (including a human) is estimated to have anywhere from 30,000 - 60,000 genes. The number of genes in organisms may vary from about 1000 (in bacteria) to more than 400,000 (in some ferns and flowering plants) How much information is held in the average organism's genome? Let's consider an average organism with 100,000 genes... The DNA of a single mammal cell, laid end to end and stretched out, would be about 1m long. (20 Angstroms in diameter) If you were to magnify this strand to the diameter of a common wrapping string (about 0.5mm), this would measure 960 km. At this magnification, there are about 50 nucleotides per cm. The full information therein, if translated into 10 pt. font and printed, would fill all 15 editions of the Encyclopedia Brittanica published since 1768! (About 20-30 volumes per edition!). Multiply this by all the individual members of a species, and then by potentially 50 million species, and you get an idea of the immeasurably vast genetic library that the earth has generated over the 3.5 billion years that life has inhabited it.
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Of what value is all this genetic information? First consider... INBREEDING (mating between closely related individuals who share many alleles of their genes--some of them harmful, recessive mutant forms) is likely to result in offspring that are homozygous for recessive alleles. Many recessive alleles (e.g., hemophilia, Sickle Cell Anemia, Tay Sachs disease etc. in humans) are deleterious, and even if they are not lethal, they may confer a selective disadvantage on the organism expressing the recessive trait.
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