Part of Dna to Determine Where Family Is From

Genome mapping is used to identify and record the location of genes and the distances between genes on a chromosome. Genome mapping provided a critical starting bespeak for the Human Genome Project.

• A genomemap highlights the key 'landmarks' in an organism'south genome.
• A bit similar how the London tube map shows the unlike stops on a tube line to help yous get around the city, a genome map helps scientists to navigate their mode effectually the genome.
• The landmarks on a genome map may include curt Dna sequences, regulatory sites that plow genes on and off or the genes themselves.
• Genome mapping provided the basis for whole genome sequencing and the Human Genome Project.
• Sequenced Deoxyribonucleic acid fragments can be aligned to the genome map to aid with the assembly of the genome.
• Over time, as scientists acquire more about a detail genome, its map becomes more accurate and detailed. A genome map is not a final production, simply piece of work in progress.

Unlike types of genome mapping

• There are ii full general types of genome mapping called genetic mapping and physical mapping.
• Both types of genome mapping guide scientists towards the location of a factor (or section of Deoxyribonucleic acid) on a chromosome, withal, they rely on very unlike information.
  • Genetic mapping looks at how genetic information is shuffled between chromosomes or betwixt different regions in the same chromosome during meiosis (a type of cell division). A process called recombination or 'crossing over'.
  • Physical mapping looks at the concrete distance between known Dna sequences (including genes) by working out the number of base pairs (A-T, C-G) between them.

Illustration showing the difference between the 2 bones means of mapping a genome: genetic mapping and concrete mapping. Image credit: Genome Enquiry Limited.

Genetic mapping

Early genetic maps

• Alfred Sturtevant created the first genetic map of a chromosome from the fruit wing (Drosophila melanogaster) in 1913.
  • He adamant that genes were arranged on chromosomes in a linear fashion, like beads on a necklace, and that genes for specific traits are located in particular places.
  • He proposed that the frequency of 'crossing over' (recombination) betwixt two genes could help determine their location on a chromosome.
  • He realised that genes that were far autonomously on a chromosome are more likely to exist inherited separately simply considering in that location is a larger region over which recombination can occur.
  • In the same style, genes that are close to each other on the chromosome are more than likely to be inherited together.

Illustration showing crossing over of chromosomes during meiosis and how this affects the likelihood of genes being inherited together. Image credit: Genome Research Limited.

• By finding out how oftentimes various characteristics are inherited together it is possible to guess the altitude betwixt the genes. A map of where the genes are in human relationship to each other on the chromosomes can then be drawn. This is called a linkage map.
• Genes that are on the same chromosome are said to be 'linked' and the distance between these genes is called a 'linkage distance'. The smaller the distance the more probable two genes will be inherited together.
• The same concept of studying how traits are passed on was applied to develop the first man genome map.
• If ii (or more) characteristics were seen to be oft inherited together in a family, for example blonde hair and blueish eyes, it suggested that the genes for the two characteristics were close together on a particular chromosome.

Illustration showing a genetic map of the chromosomes from the fruit fly (Drosophila melanogaster). The names of the genes are shown to the correct of each chromosome. The numbers to the left of each chromosome represent the distance between these genes. Prototype credit: Genome Inquiry Limited.

Modern genetic maps

• With more recent genetic mapping techniques, the position of genes is worked out from finding the exact frequency of genetic recombination that has occurred.
• To produce a genetic map, researchers collect blood or tissue samples from members of a family, some of whom take a certain disease or feature.
• The researchers then isolate the Deoxyribonucleic acid from samples taken from each private and closely examine it to observe unique patterns in the DNA of those individuals with the disease/characteristic, that aren't present in the DNA of the individuals who don't accept the affliction/characteristic.
• These are referred to as markers and are extremely valuable for tracking inheritance of characteristics or diseases through several generations of a family.
• One type of Deoxyribonucleic acid marker, called a microsatellite, is found throughout the genome and consists of a specific repeated sequence of bases.
• If a particular gene is close to a Deoxyribonucleic acid marker on the chromosome, it is more probable that the gene and marker will stay together during the recombination procedure and are therefore more probable to exist passed down along the family unit line (inherited) together.
• In the same way, if a DNA mark and gene are oftentimes separated by the recombination procedure it suggests that they are far apart on the chromosome and are less likely to be inherited together.
• The more Deoxyribonucleic acid markers there are on a genetic map the more likely it is that one of them will exist located close to the disease or trait-associated gene.
• While genetic maps are good at giving you lot the bigger picture, they have express accuracy and therefore need to be supplemented with further information gained from other mapping techniques, such as physical mapping.

Physical mapping

• Physical mapping gives an estimation of the (physical) distance betwixt specific known Dna sequences on a chromosome.
• The distance between these known DNA sequences on a chromosome is expressed as the number of base pairs between them.
• In that location are a several different techniques used for physical mapping. These include:
  • Restriction mapping (fingerprint mapping and optical mapping)
  • Fluorescent in situ hybridisation (FISH) mapping
  • Sequence tagged site (STS) mapping.

Restriction mapping

• This uses specific restriction enzymes to cutting an unknown segment of DNA at curt, known base sequences called brake sites.
• Brake enzymes always cut DNA at a specific sequence of Dna (restriction site). For example, the restriction enzyme EcoRI (taken from Escherichia coli) always cuts at the sequence GAATTC/CTTAAG. Therefore if we use EcoRI to cut the DNA we know that the DNA sequence either side of the cut will be AATT (see effigy below).
• A restriction map shows all the locations of that particular restriction site (GAATTC) throughout the genome.
• A physical map is generated past adjustment the different restriction maps forth the chromosomes.
• There a 2 specific types of restriction mapping – optical and fingerprint.

Analogy showing the restriction site for the restriction enzyme EcoRI. Brake enzymes always cut DNA at a specific sequence of DNA. Image credit: Genome Inquiry Limited.

Fingerprint mapping

• In fingerprint mapping the genome is cleaved into fragments which are and so copied in bacteria cells.
• The DNA copies (clones) are then cutting past brake enzymes and the lengths of the resulting fragments are estimated using a lab method called electrophoresis.
• Electrophoresis separates the fragments of Deoxyribonucleic acid co-ordinate to size resulting in a distinct banding pattern.

Illustration showing how a Dna fingerprint is created by electrophoresis. Image credit: Genome Research Limited.

• The fingerprint map is constructed by comparison the patterns from all the fragments of Dna to find areas of similarity. Those with similar patterns are so grouped together to form a map.
• Fingerprint mapping formed the footing to the sequencing of the man, mouse, zebrafish and pig genomes.

Illustration showing how Deoxyribonucleic acid fingerprints tin can be compared to produce a genome map. Epitome credit: Genome Research Limited.

Optical mapping

• Optical mapping uses single molecules of Deoxyribonucleic acid that are stretched and held in place on a slide.
• Restriction enzymes are added to cut the DNA at specific points leaving gaps behind.
• The fragments are then stained with dye and the gaps are visualised nether a fluorescence microscope.
• The intensity of the fluorescence is used to construct an optical map of single molecules.
• These can then be combined and overlapped to give a global overview of the genome and aid with assembling a sequenced genome.

Illustration showing the procedure of optical mapping. Image credit: Genome Research Express.

Fluorescent in situ hybridisation (FISH) mapping

• This uses fluorescent probes to detect the location of DNA sequences on chromosomes.
• First, the probes are prepared. These are short sequences of single-stranded DNA, that match the Deoxyribonucleic acid sequence that the scientist wants to find.
• The probes are then labelled with fluorescent dye before beingness mixed with the chromosome Dna so that it tin demark to a complementary strand of Dna on the chromosome.
• The fluorescent tag allows the scientist to come across the location of the DNA sequence on the chromosome.

Illustration showing how FISH can exist used to produce a genetic map. The photograph on the left shows Chromosome 17 from four British peppered moths with fluorescent probes indicating the physical positions of specific genes. The illustration on the right shows the relative positions of the genes on the chromosome. Image credit: Adjusted from The American Association for the Advancement of Science (DOI: x.1126/science.1203043)

Sequence-tagged site (STS) mapping

• This technique maps the positions of short Deoxyribonucleic acid sequences (between 200-500 base pairs in length) that are easily recognisable and simply occur once in the genome. These curt Dna sequences are chosen sequence-tagged sites (STSs).
• To map a set of STSs a collection of overlapping DNA fragments from a single chromosome or the entire genome is required.
• To do this, the genome is starting time broken upwardly into fragments.
• The fragments are then replicated upward to 10 times in bacterial cells to create a library of DNA clones.
• The polymerase chain reaction (PCR) is and so used to determine which fragments incorporate STSs. Special primers are designed to bind either side of the STS to ensure that merely that part of the DNA is copied.
• If two DNA fragments are found to contain the same STS then they must correspond overlapping parts of the genome.
• If ane Dna fragment contains two different STSs then those two STSs must be nigh to each other in the genome.

Analogy showing the process of STS mapping. Image credit: Genome Research Limited.

This page was last updated on 2021-07-21

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Source: https://www.yourgenome.org/facts/how-do-you-map-a-genome

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