PopulationGeneticsNotes updated 11-29-2015 - Population...

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Updated 11-29-2015 Population Genetics Is an extension of Mendel's ideas to the study of genetics at the population level. Population genetics seeks to understand: 1. HOWinherited traits are distributed in diverse groups of people, or groups of a particular species. 2. WHYthe statistics that apply to genetic conditions may change over time. Consider the following example: The very slow frequency changes over time of the rare recessively inherited disease phenylketonuria, PKU, expected when treated individuals live long enough to reproduce. Consider another example: The recessive allele which confers sickle-cell anemia in humans in the homozygous state "...is maintained through selective advantage of the heterozygotes, which are somewhat resistant to the protozoan (Plasmodium falciparum) that causes malaria if transmitted into the bloodstream by an Anopheles mosquito." [Redei, 1982] Ask questions: 1. How much responsibility should any generation accept for the genetic material that it transmits to the next generation? 2. How much harm is produced when medical science allows individuals with genetic disorders to live well enough and long enough to reproduce? 3. At what cost to society? 4. How does this affect our approach or point of view in the search to find new/better treatments or "cures" for genetically determined diseases? 5. What is the probability that a gene responsible for a genetic disorder is altered over time such that it confers a normal genotype or the environment changes such that those who inherit it have a genetic advantage relative to the rest of the population? It is through population genetics that we can examine these types of questions and make predictions on the genetic make-up of future generations. Population: A collection, or group, of interbreeding individuals from a single species.Frequency: The term used to describe the proportion of a certain type within a population.Genotype frequency: The proportion of a population that is a particular genotype. Expressed as a percentage or decimal fraction. If the possible genotypes for a single locus in a population, of diploid individuals in a two allele system, are: AAAaaaThen the frequency of each genotype would be expressed as: freq(AA) freq(Aa) freq(aaPhenotype frequency: The proportion of a population that is a particular phenotype. Expressed as a percentage or decimal fraction. Consider the following: Case #1 If Gene A is a two-allele system, and each genotype in a population corresponds to a different phenotype, then Genotype frequency = Phenotype frequency Genotypes Phenotypes Genotype Frequency = Phenotype Frequency AA red freq(AA) Aa pink freq(Aa) aa white freq(aa) 1 )
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Understanding Basic Statistics
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Chapter 5 / Exercise 3
Understanding Basic Statistics
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Updated 11-29-2015 2

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