EvolutionPrinciples160

EvolutionPrinciples160 - Principles of Evolution - 1 We...

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Principles of Evolution - 1 We have seen in this course that recombination, segregation of alleles, and independent assortment of homologous chromosomes during meiosis results in the variation that occurs among individuals in populations. We have seen, too, that mutation is a source of increasing variation within populations. Each individual's phenotype depends on how the alleles he or she inherits interact in gene expression. Some inheritance patterns, such as multiple alleles of a single gene, and the continuous variation resulting from polygenic inheritance, are observed only within the framework of population genetics. We have also learned that the frequency of a gene (or specifically, an allele) affects its appearance in populations. For example, in human blood types, B is a co-dominant allele, though not common within most populations, so that O and A phenotypes are much more abundant. In the next few lectures we will look at variations that appear within populations with reference to the way an individual "contributes" to the population's genetic mix or gene pool, and how this gene pool is changed from generation to generation, which is the study of evolutionary biology. As an introduction, let's begin with a working biological definition of evolution, to avoid the confusion and misconceptions that sometimes surround this term. Evolution is biologically defined as the change in the frequency of a gene's (or allele's) appearance in a population's gene pool from generation to generation (through time). More simply, evolution is inheritable change in organisms over time. Note the following components to evolution: The importance of genetics - the frequency of a gene's appearance The importance of time - in generations The importance of populations - the aggregate of individuals It will also help to define what a species is: A species is a population of organisms that is naturally capable of interbreeding among themselves, but does not interbreed with other populations of different species. If interbreeding occurs, the offspring are infertile or less viable in some way. As with most of what we study today in biology, the field of evolutionary biology has interesting beginnings.
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Principles of Evolution - 2 Throughout recorded history, humans have been trying to find natural explanations for our observations of events around us, including explanations for the vast diversity of organisms that inhabit this earth with us. Humans of all cultures have always tried to group, or classify organisms, in attempts to clarify what has been observed. One of the concerns in classification was to determine what comprised a unique group of organisms, what we now call a species, a question still debated to some extent today. In earlier centuries, most considered visual characteristics for defining groups or species; today, we mostly use reproductive isolation as the major determinant of a species. In the 1700's Linneaus developed the classification system in use today - binomial nomenclature. Each species is given a
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EvolutionPrinciples160 - Principles of Evolution - 1 We...

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