pop_genet - Population Genetics Evolution by Natural...

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Population Genetics
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Evolution by Natural Selection Unlike Mendel, Charles Darwin made a big splash when his defining work, "On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life" (which we refer to as “The Origin of Species”) published in 1859. Darwin set forth a scientific theory that described how one species could give rise to another species, given sufficient time. It was heavily attacked at the time (and continuing to this day) by people who thought that it contradicted their religious beliefs. Nevertheless, the basic theory has survived and flourished, and today it is one of the main pillars of biological theory.
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Fitness A fundamental concept in evolutionary theory is “fitness”, which can defined as the ability to survive and reproduce. Reproduction is key: to be evolutionarily fit, an organism must pass its genes on to future generations. Basic idea behind evolution by natural selection: the more fit individuals contribute more to future generations than less fit individuals. Thus, the genes found in more fit individuals ultimately take over the population. Natural selection requires 3 basic conditions: 1. there must be inherited traits. 2. there must be variation in these traits among members of the species. 3. some inherited traits must affect fitness
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Genetics of Populations Darwin didn’t understand how inheritance worked--Mendel’s work was still in the future. It wasn’t until the 1930’s when Mendelian genetics was incorporated into evolutionary theory, in what is called the “Neo-Darwinian synthesis”. Translated into Mendelian terms, the basis for natural selection is that alleles that increase fitness will increase in frequency in a population. Thus, the main object of study in evolutionary genetics is the frequency of alleles within a population. A “population” is a group of organisms of the same species that reproduce with each other. There is only one human population: we all interbreed. The “gene pool” is the collection of all the alleles present within a population. We are mostly going to look at frequencies of a single gene, but population geneticists generally examine many different genes simultaneously.
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Allele and Genotype Frequencies Each diploid individual in the population has 2 copies of each gene. The allele frequency is the proportion of all the genes in the population that are a particular allele. The genotype frequency of the proportion of a population that is a particular genotype. For example: consider the MN blood group. In a certain population there are 60 MM individuals, 120 MN individuals, and 20 NN individuals, a total of 200 people. The genotype frequency of MM is 60/200 = 0.3.
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This note was uploaded on 12/24/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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pop_genet - Population Genetics Evolution by Natural...

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