A reference genome (also known as a reference assembly) is a digital nucleic acid sequence database, assembled by scientists as a representative example of the set of genes in one idealized individual organism of a species. As they are assembled from the sequencing of DNA from a number of individual donors, reference genomes do not accurately represent the set of genes of any single individual organism. Instead a reference provides a haploid mosaic of different DNA sequences from each donor. For example, the most recent human reference genome (assembly GRCh38/hg38) is derived from >60 genomic clone libraries. There are reference genomes for multiple species of viruses, bacteria, fungus, plants, and animals. Reference genomes are typically used as a guide on which new genomes are built, enabling them to be assembled much more quickly and cheaply than the initial Human Genome Project. Reference genomes can be accessed online at several locations, using dedicated browsers such as Ensembl or UCSC Genome Browser.
The length of a genome can be measured in multiple different ways.
A simple way to measure genome length is to count the number of base pairs in the assembly.
The golden path is an alternative measure of length that omits redundant regions such as haplotypes and pseudoautosomal regions. It is usually constructed by layering sequencing information over a physical map to combine scaffold information. It is a 'best estimate' of what the genome will look like and typically includes gaps, making it longer than the typical base pair assembly.
Reference genomes assembly requires reads overlapping, creating contigs, which are contiguous DNA regions of consensus sequences. If there are gaps between contigs, these can be filled by scaffolding, either by contigs amplification with PCR and sequencing or by Bacterial Artificial Chromosome (BAC) cloning. Filling these gaps is not always possible, in this case multiple scaffolds are created in a reference assembly.
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Ce cours présente les principes fondamentaux à l'œuvre dans les organismes vivants. Autant que possible, l'accent est mis sur les contributions de l'Informatique aux progrès des Sciences de la Vie.
This course covers various data analysis approaches associated with applications of DNA sequencing technologies, from genome sequencing to quantifying gene expression, transcription factor binding and
High-throughput methodologies broadly called Omics allow to characterize the complexity and dynamics of any biological system. This course will provide a general description of different methods relat
Whole genome sequencing (WGS), also known as full genome sequencing, complete genome sequencing, or entire genome sequencing, is the process of determining the entirety, or nearly the entirety, of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's chromosomal DNA as well as DNA contained in the mitochondria and, for plants, in the chloroplast. Whole genome sequencing has largely been used as a research tool, but was being introduced to clinics in 2014.
In genetics, shotgun sequencing is a method used for sequencing random DNA strands. It is named by analogy with the rapidly expanding, quasi-random shot grouping of a shotgun. The chain-termination method of DNA sequencing ("Sanger sequencing") can only be used for short DNA strands of 100 to 1000 base pairs. Due to this size limit, longer sequences are subdivided into smaller fragments that can be sequenced separately, and these sequences are assembled to give the overall sequence.
Ensembl genome database project is a scientific project at the European Bioinformatics Institute, which provides a centralized resource for geneticists, molecular biologists and other researchers studying the genomes of our own species and other vertebrates and model organisms. Ensembl is one of several well known genome browsers for the retrieval of genomic information. Similar databases and browsers are found at NCBI and the University of California, Santa Cruz (UCSC).
Growing evidence indicates that transposable elements (TEs) play important roles in evolution by providing genomes with coding and non-coding sequences. Identification of TE-derived functional elements, however, has relied on TE annotations in individual s ...
How chronic mutational processes and punctuated bursts of DNA damage drive evolution of the cancer genome is poorly understood. Here, we demonstrate a strategy to disentangle and quantify distinct mechanisms underlying genome evolution in single cells, dur ...
Nature Portfolio2024
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Vibrio cholerae has caused seven cholera pandemics in the past two centuries. The seventh and ongoing pandemic has been particularly severe on the African continent. Here, we report long read-based genome sequences of six V. cholerae strains isolated in th ...