Population_Genetics_revised_-_sec._3

Population_Genetics_revised_-_sec._3 - Population Genetics...

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Population Genetics Purpose of the lab exercises: Introduction to the Hardy-Weinberg theory Understanding the assumptions underlying the H-W theory An interactive demonstration of the theory “in action”, and observations on the effects of violating the assumptions
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Hierarchies of Biological Order Life can be viewed as organized on a series of levels, with each higher level having emergent properties compared to the level below it.
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Hierarchies of Biological Order The study of genetics can be confusing to students, because it is explored on a number of different levels of organization. For example, in the lab on mitosis and meiosis, you studied genetics at the organelle and “ cellular levels. Continued
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Hierarchies of Biological Order In the lab on Mendelian genetics, you were making observations at the “ organism ” level. The lab on molecular biology was concerned with genetics at the molecular level of organization.
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Hierarchies of Biological Order In today’s lab, you will be studying genetics at the level of the population . A population can be defined as a group of individuals of one species that live in a particular geographic area.
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Genes, Alleles, and Chromosomes Before discussing the Hardy-Weinberg theory of population genetics, let’s review the relationship among genes, alleles, and chromosomes. In diploid organisms, chromosomes in somatic cells occur in pairs, called homologous chromosomes.
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A gene is a discrete unit of heredity consisting of a specific nucleotide sequence in the DNA. Each member of the homologous pair has genes at the same loci. The alternative forms of a gene are called “ alleles ”. The 2 alleles of a pair may be the same, or they may be different. Genes, Alleles, and Chromosomes
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Genes, Alleles, and Chromosomes As a result of meiosis, gametes (eggs & sperm) contain only ONE member of the pair of homologous chromosomes. Therefore, for any given gene, a parent contributes only ONE allele. Meiosis
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Let’s assume we have a gene for which there are 2 alleles: a A Genes, Alleles, and Chromosomes A diploid individual can have one of three possible allele combinations: A A A a a a Homozygous Homozygous Heterozygous
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In a cross between 2 heterozygous individuals, the gametes of the parents, as well as the genotypes and expected ratios of progeny, are represented in the figure to the left. Be sure you understand this figure, as we’ll come back to it again later. Chance Segregation of Alleles and Fertilization Aa Aa A A a a A A A A a a a a
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Next let’s consider allele frequencies . The frequency of an allele is the proportion it represents of the total number of alleles in the population. Allele frequencies are represented in decimal form, between 0 and 1.0.
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Population_Genetics_revised_-_sec._3 - Population Genetics...

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