Population genetics lecture notes

Population genetics lecture notes - Population genetics...

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Population genetics Population genetics is a field that could be viewed as the extension of Mendelian genetics to the population level, rather than a consideration of the gene segregation within a cross or family. While a single diploid individual can have at most two alleles for some gene, in a population there can be numerous alleles at various frequencies. In population genetics, descriptions can be made of the frequencies of various genotypes and alleles in populations, and/or the levels of genetic variation can be determined. A population is a collection of organisms of a single species the individuals of which interact with each other in some way. So, a species will typically be broken up into a number of populations. Population genetics includes both empirical and theoretical studies. It provides the mechanics or mathematics underlying the evolutionary process, and it emerged in the 1920's. The main founders include RA Fisher, JBS Haldane, and Sewall Wright. The increasing availability of DNA sequence data, faster computers, and mathematics, have continued to fuel this field. Population genetics is also relevant in applied fields including agriculture, medical genetics including the genetics of various human diseases, and in the evolution of bacterial resistance to antibiotics, and the evolution of virulence in pathogens. Questions in population genetics: 1. What are the levels of genetic variation in populations? 2. How do different mating patterns affect genotype and allele frequencies? 3. What forces are responsible for changes in allele frequencies or the genetic composition of populations? In otherwords, what are the roles of mutation, migration, genetic drift and natural selection in populations. Genetic variation Genetic variation is critically important from both theoretical and applied perspectives. In the absence of genetic variation, evolution cannot occur. Likewise, in order to improve crop plants or animals for breeding purposes there must be genetic variation present. One of the first tasks in population genetics is the measurement of variation within populations. The easy way to approach this is to make use of single genes that are co- dominant (or show additive inheritance or incomplete dominance) where there is a one to one correspondence between the genotype and phenotype (for quantitative or polygenic traits, other approaches are necessary).
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Among the first loci used to assess levels of variation in human populations were various blood group loci, including the ABO blood group system and the MN blood group polypmorphism. MN blood group polymorphisms So let's consider an example involving the MN blood group polymorphism. The gene has two codominant alleles in populations, M and N. And with a simple blood test one can determine the the genotype of individuals as MM, MN or NN. So let's imagine you have the following sample of from a population
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Population genetics lecture notes - Population genetics...

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