Difference Between Genetic and Physical Mapping

The Human Genome Project (HGP) had as one of its key objectives the creation of new, improved, and more affordable methods for discovering new genes and comprehending their function. Genetic mapping is one of these tools. Linkage mapping, another name for genetic mapping, can provide solid proof that a condition passed from parent to the kid is connected to one or more genes.

When a gene is mapped, it is possible to determine which chromosome it is located on and with what accuracy. Genetic mapping has been successfully used to pinpoint the gene for relatively uncommon, single-gene hereditary disorders, including cystic fibrosis and Duchenne muscular dystrophy. Researchers have also used genomic mapping to find the various genes that are thought to play a role in the emergence of disease.

An estimate of the physical separation between particular recognised DNA sequences on a chromosome is provided by physical mapping. The number of base pairs separating these recognised DNA sequences on a chromosome is used to express their separation. For physical mapping, a variety of techniques are employed. These consist of - Restriction mapping (fingerprint mapping and optical mapping), mapping using fluorescent in situ hybridisation (FISH), and mapping using a sequence tagged site (STS).

Types of Gene Mapping

Genetic Mapping

To determine the relative location of genes on a chromosome, genetic mapping is utilised. So as to determine the relative distance and inheritance pattern, recombination and linkage studies are used. The method of mapping starts with the collection and DNA isolation of samples from close relatives. These DNAs are carefully examined to get the polymorphisms that act as our genetic markers. The mapping provides a prediction of whether or not the genes will recombine. Centimorgans, named for the scientist Thomas Hunt Morgan, are made to measure distance.

What is Genetic Map?

A genetic map, also known as a linkage map, demonstrates the relative positions of genetic markers indicating the locations of genomic variants on a chromosome. A genetic map is based on the idea of genetic linkage, which states that the likelihood that two markers on a chromosome will be inherited together increases the closer they are to one another. It is possible to determine the relative positioning and order of genetic markers along a chromosome by looking at inheritance patterns.

Genetic Mapping Techniques

Recombination events are used by genetic mapping tools to calculate the separation between genetic markers. RFLP, or Random Fragment Length Polymorphism, studies the variations in homologous DNA sequences to identify the distance between two markers.

With the help of restriction enzymes, the DNA segment is broken up into restriction fragments that are cleaved at particular restriction sites. Using gel electrophoresis, these fragments are divided based on the length of the segments. The use of two or more RFLP loci is required for genetic mapping. Using Southern blotting, the parental and recombinant fragments are distinguished, and their frequency is noted.

Physical Mapping

In terms of nucleotides, physical mapping offers the precise physical separation between genetic markers. Different methods, like restriction mapping, fluorscence in situ hybridisation mapping, or sequencing tag site mapping, can be used to accomplish this. In the restriction mapping technique, the DNA sequences are cut using restriction enzymes, then the fragments are separated by electrophoresis. The DNA is analysed, and maps are created using the migration pattern.

Physical Mapping of Genome

A graphical representation of the physical positions of landmarks or markers (such as genes, variations, and other interesting DNA sequences) within a chromosome or genome is known as a physical map in the field of genomics. One kind of physical map is a genome’s full sequence.

Difference Between Genetic and Physical Mapping

Physical maps support actual physical distances determined by the number of base pairs, whereas genetic maps support genetic linkage information. This is often the main distinction between genetic and physical mapping. The two key components of genetic mapping are genetic markers and the size of the mapping population. However, physical mapping necessitates either physical shattering of the genome or restriction digestion to fragment the genome. Furthermore, physical maps are a more realistic picture of the genome than genetic maps, which regularly provide insights into the nature of certain chromosomal regions.

Uses of Gene Mapping

• Genetic mapping It is a map of our genome that is found on chromosomes, as the name would imply.

• Describes the order of genes or other markers and the spacing between them on each chromosome.

• Scientists separate DNA, test it for diseases and traits, and then use DNA markers to pinpoint the gene that is responsible for each trait.

• The relative positions of particular DNA markers along the chromosome are displayed on genetic linkage maps.

• Physical maps These maps, as opposed to linkage maps, may pinpoint the precise location of a gene’s location on a chromosome. Various methods 1 Somatic cell hybridisation 2 Radiation hybridisation 3 Fish (Fluorescent In Situ Hybridization).

Interesting Facts

• In order to use the genes or characters on the chromosome in genetic studies, genetic maps are made.

• Alfred H. Sturtevant mapped the relative positions of a number of genes on a chromosome in 1913, helping to create the groundwork for modern Biology.

Important Questions

1. What is the short gun method?

Ans: Short gun method is the method of sequencing in which DNA is digested into small fragments, which are then sequenced separately. The overlaps between the sequences are used to fill the gaps. This method removes errors and fills the gaps so that the genome sequence is accurate.

2. What is Sanger's method of sequencing?

Ans: Sanger sequencing is a chain termination method for sequencing 100 to 1000 bp. It involves three basic steps namely:

• Chain termination PCR.

• Separation of fragments by electrophoresis.

• Gel analysis to determine the DNA sequence.

Key Features

• Physical and genetic mapping are continuing research projects that will go further in the future. Physical mapping provides the specifics, while genetic mapping only provides a chromosome’s general shape. To investigate the chromosomes, information from both maps is integrated.

• In the Indian Ocean, India has begun genome mapping. To better comprehend the biochemistry of the ocean and how it responds to nutrient stress, pollution, and climate change, the nation is conducting a first-of-its-kind study initiative.

• The frequency of a chromosomal crossing between two loci (or genes) during meiosis is known as recombination frequency. A genetic linkage map is made using recombination frequency, a measure of genetic connection.