IB31Lecture+3+Outline+Sp08 - IB 31, Sp. 2008 Jan. 29, 2008...

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IB 31, Sp. 2008 Jan. 29, 2008 Caldwell, Evolution and Natural Selection I Central to almost every aspect of Modern Biology is Evolution based on the concept of Natural Selection, as formulated by Darwin and Wallace, and substantiated and modified by later scientists. To understand modern behavioral biology, it is essential that you understand these processes. This will be old hat for some of you, but it is so important to understanding behavior that I want to make sure that the class starts on a solid foundation. Therefore, if you have had this before, please bare with me. If you are having difficulty with evolutionary concepts, try logging onto our UC Berkeley website, Understanding Evolution: http://evolution.berkeley.edu/evolibrary/home.php. I. EVOLUTION, as we now understand it, is a change in the genetic composition of a population. (For our purposes, a population is a group of potentially interbreeding individuals.) Usually, the changes we are concerned with are in the relative frequencies of particular forms of a gene. Different forms of a gene are called ALLELES. For example, in humans, a particular gene may be one of many involved in the production of the skin pigment melanin. The normal genetic instructions at this locus promote melanin production. This is called the “normal” allele. A defective set of genetic instructions at this same locus might block pigment production and produce albinism. If you inherited two copies of this allele, you would be an albino. (Remember from your basic biology, we have two sets of genetic instructions carried on pairs of autosomal chromosomes. Each chromosome of a pair has one copy (allele) of a particular gene found at a particular location on that chromosome.) One normal allele is sufficient to produce melanin. Typically, the frequency of albino alleles is very rare in human populations - much less than 1%, and there are very few albinos. In fact, there may be some selection against this condition due to UV exposure causing skin and eye cancer. However, if for some reason albinos in a population were favored and were more likely to reproduce, the allelic frequency of the albinism form of the gene would increase (Cuna Indians of the San Blas – moon children), there would be more albinos and we would say that the population had evolved - there was a change in gene frequency! Evolution can also occur when there are changes in the structure of chromosomes and the arrangement of genes on them, affecting how genes are expressed and inherited or how genes are switched on and off, but for our purposes, we will be primarily concerned with changes in gene frequencies. II. Lets look at one well-documented case of evolution - a rare instance where we have been able to observe the process in action - INDUSTRIAL MELANISM. This is a classic example used in many text books, but I want to concentrate on how we deduce the mechanisms underlying evolutionary change. A.
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This note was uploaded on 04/02/2008 for the course IB 31 taught by Professor Caldwell during the Spring '08 term at University of California, Berkeley.

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IB31Lecture+3+Outline+Sp08 - IB 31, Sp. 2008 Jan. 29, 2008...

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