Genomics I - Genomics I: Analysis of DNA Introduction The...

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1 Genomics I: Analysis of DNA Introduction The total genetic composition of an organism is its genome. Genomics is the molecular analysis of the entire genome of a species. The first complete sequence of a genome was obtained in 1995 by Venter and Smith. The genome of the bacterium Hemophilus influenzae is composed of a single circular chromosome 1.83 million base pairs (bp) in length containing approximately 1,743 genes (Figure 20.1). The first complete eukaryotic genome that was sequenced was Saccharomyces cerevisiae. It contains 16 linear chromosomes with a combined length of about 12.1 million bp and approximately 6,300 genes. Functional genomics studies the interaction of the components of the genome to produce the traits of the organism. Proteomics studies the interactions of all cellular proteins to produce the characteristics of particular cell types and the traits of complete organisms. Cytogenetic and Linkage Mapping General information. Mapping refers to the experimental process of determining the relative locations of genes or other segments of DNA along individual chromosomes. There are three ways to determine the organization of DNA regions. Cytogenetic mapping (cytological mapping) relies on the localization of gene sequences within chromosomes that are viewed using a microscope. Linkage mapping (genetic mapping) uses the frequency of recombination between different genes to determine their relative spacing and order along a chromosome. Physical mapping uses DNA cloning techniques to determine the location of and distance between genes and other DNA regions in nucleotide base pairs. A genetic map is a chart that describes the relative locations of genes and other DNA segments along a chromosome.
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2 The term locus (pl., loci) refers to the site within a genetic map where a specific gene or other DNA segment is found. Figure 20.2 compares genetic maps produced by the three mapping methods showing the loci for two X-linked genes in Drosophila melanogaster . A goal of cytogenetic mapping is to determine the location of genes along an intact chromosome. Eukaryotic chromosomes may be distinguished by their size, centromeric location, and banding patterns. By treating chromosomal preparations with particular dyes, a discrete banding pattern is obtained for each chromosome. The banding pattern can be used to describe specific regions along a chromosome. Cytogenetic mapping attempts to locate particular genes relative to the banding pattern of a chromosome. For example, the human gene that is defective in people with cystic fibrosis, the gene that encodes the transmembrane regulator, is located on chromosome 7 at a specific site in the q 3 region. In Situ
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Genomics I - Genomics I: Analysis of DNA Introduction The...

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