The Human Genome Project aimed to produce four types of map: physical, genetic, DNA sequence and gene. Physical and genetic maps provide essential anchor points and frameworks to align DNA sequences and assign genes. A high-resolution physical map based on the analysis of overlapping DNA clones represents the actual distance in DNA base pairs between genetic markers and other landmarks. However, the ultimate physical map is the DNA sequence itself. Low-resolution physical maps are generated from techniques such as somatic cell hybridisation and fluorescence in situ hybridisation; these methods are also applicable for assigning genes to chromosomes.
There are two approaches to genome sequencing: whole genome shotgun sequencing (WGS) and the more labour-intensive hierarchical shotgun sequencing (HS). In simple organisms such as bacteria and viruses, where the chromosomes are haploid and very little repeat sequence occurs, or for sequencing individual human genes, WGS works well. In contrast, for eukaryotic genomes, where repeat sequences often abound, including the human genome (>50% repeats), and there is considerable heterozygosity, it has been argued that HS offers advantages over WGS, and this was the approach adopted by the publicly funded International Human Genome Sequencing Consortium.
There are two approaches to genome sequencing: whole genome shotgun sequencing (WGS) and the more labour-intensive hierarchical shotgun sequencing (HS). In simple organisms such as bacteria and viruses, where the chromosomes are haploid and very little repeat sequence occurs, or for sequencing individual human genes, WGS works well. In contrast, for eukaryotic genomes, where repeat sequences often abound, including the human genome (>50% repeats), and there is considerable heterozygosity, it has been argued that HS offers advantages over WGS, and this was the approach adopted by the publicly funded International Human Genome Sequencing Consortium.
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