Gene Mapping – Types, Methods, and Techniques

Gene mapping is finding and locating the precise location of genes on a chromosome or genome. It involves creating a map showing the relative locations of genes and other genetic markers throughout the length of chromosomes. Gene mapping was given by Thomas Hunt Morgan.

Gene mapping techniques include genetic linkage, physical, and comparative genomic mapping. It is an essential genetic tool for disease gene discovery, pharmacogenomics, crop improvement, and forensic genetics. In this article, we will look into the Gene Mapping definition, examples, types, methods, importance, and application of gene mapping.

What is Gene Mapping?

Gene Mapping Definition: Gene mapping or genome mapping is the process of determining the distance between genes and their location on the chromosome with the help of genetic markers and recombination probabilities.

Gene mapping is the process by which gene maps are created to give a diagrammatic representation of a list of genes and their location on the chromosome. A gene map gives the distance between the genes in the centimorgan (cM) unit. It is the method in which the location of a gene within a chromosome is specified, and the distance between two or more genes can be determined. It is a tool that utilizes genetic markers specific to an organism to know the location and distance between genes in a chromosome.

Genetic Markers

Genetic markers are particular DNA sequences used to identify the location of genes or other genomic regions. Gene markers are polymorphic DNA sequences generally associated with a specific trait in all organisms. Gene markers are usually targeted based on their polymorphic forms in different organisms.

Genetic markers can be variations in the DNA sequence, such as single nucleotide polymorphisms (SNPs), insertions, deletions, or repeats. These markers are typically inherited along with nearby genes, showing the linkage used to create genetic maps.

Gene Mapping Examples

One of the best gene mapping or genome mapping examples is Drosophila melanogaster genetic linkage map given by Thomas Hunt Morgan. This map showed that the distance between two genes was approximately equal to their recombination frequency. If two genes had a recombination frequency of 25% then their distance in the chromosome was approximately 25 cM.

Genes that are closer showed a higher recombination frequency are closer together while genes that have recombination frequency more than or equal to 50% are said to be independently assorted or non-linked.

Types of Gene Mapping

Based on the analysis technique of genetic markers, there are three types of gene mapping. These are:

Genetic Linkage Mapping

In this type of gene mapping, linkage analysis between two genes is done to predict the distance between them and their chromosome location. This method involves tracking the inheritance patterns of genetic markers, such as single nucleotide polymorphisms (SNPs) or microsatellites, within families to identify regions of chromosomes associated with specific traits or diseases.

Physical Gene Mapping

Physical gene mapping involves examining and sequencing DNA molecules to determine their precise nucleotide sequences and physical locations within a genome. Techniques such as fluorescence in situ hybridization (FISH) and next-generation sequencing (NGS) are commonly used to pinpoint the gene’s position in the chromosome.

Whole genomes can be sequenced, and the known gene can be located based on sequencing data, or chromosomes can be labeled with fluorescent probes complementary to the gene of interest and then visualized under fluorescent microscopes to determine the location of the gene on the chromosome.

Gene Mapping and Linkage Analysis

Linkage analysis is a technique to investigate the inheritance patterns of genes and genetic markers in and among families. Linkage analysis checks for co-inheritance of genetic markers and traits of interest to identify chromosomal areas likely to contain genes related to those genes.

Linkage analysis is based on the idea that genes that are next to each other in the same chromosome are inherited or linked during meiosis. This condition is referred to as Genetic linkage. Genetic mapping utilizes linkage analysis to determine the location of genes by analyzing their transmission pattern among individuals to understand whether genes are close (strongly linked) or far (not linked). LOD score is used to determine the strength of the linkage of genes.

Types of Gene Mapping Techniques

Various methods are used to map genes. The techniques of gene mapping are:

• RFLP (Restriction Fragment Length Polymorphism): RFLP is a genetic marker that analyses gene variants caused by variations in DNA sequences recognized by restriction enzymes, thus giving different lengths of fragments in digestion. Differences in DNA sequences between individuals are determined by analyzing the resulting fragment sizes.
• SNP (Single Nucleotide Polymorphism): SNP is a common genetic variation characterized by a single nucleotide mutation in the DNA sequence. SNPs occur frequently in the human genomes and are often used to map genes.
• GWAS (Genome-Wide Association Study): GWAS involves scanning the whole genomes of individuals to identify genetic variants associated with specific traits or diseases. This technique typically analyzes hundreds of thousands to millions of genetic markers across the genome to identify associations between genes, their positions, and variants.
• FISH (Fluorescence in Situ Hybridization): FISH is a cytogenetic technique that visualizes and maps the positions of specific DNA sequences on chromosomes. Labeled DNA probes with fluorescent dyes are hybridized into specific DNA sequences in cells or tissue samples to determine the position of genes on chromosomes.
• Next-Generation Sequencing (NGS): NGS is a high-throughput DNA sequencing method that enables the quick and cost-effective sequencing of many DNA fragments. This technology has many applications, including whole-genome sequencing, gene mapping, exome sequencing, transcriptome analysis, and metagenomics.

Importance of Gene Mapping

Genome mapping is an important genetic tool that has various important uses such as:

• It can identify genes that are near to each other and therefore understand their recombination frequency and mode of transmission.
• It can be used to study the genes associated with a specific trait like eye colour in Drosophila.
• It is used to study genes associated with diseases.
• It is used to crate whole genome maps to understand the position and location of all genes in an organisms.

Applications of Gene Mapping

Gene mapping or genome mapping is a promising and developing field of study with several applications today:

• Disease Gene Mapping: Gene mapping can identify genetic variants associated with various diseases, including cancer, cardiovascular disorders, and neurodegenerative conditions.
• Pharmacogenomics: Knowing the position of a defective or disease-causing gene allows the development of targeted, personalized medications, known as pharmacogenomics.
• Crop Improvement: In agriculture, gene mapping is utilized to identify genes responsible for desirable crop traits, such as disease resistance, yield potential, and nutritional quality. This knowledge aids in developing genetically modified (GM) crops with enhanced characteristics and yields.
• Forensic Genetics: Gene mapping techniques are employed in forensic genetics to analyze DNA evidence and identify individuals in criminal investigations, paternity testing, and mass disaster victim identification.

Conclusion – Gene Mapping

Overall, gene mapping or genome mapping is the technique in which the location and distance of and between genes are located on the chromosome. It can be done by physical or linkage mapping and has multiple applications in health, criminology, pharmacogenetics, plant improvement, and disease.

FAQs on Gene Mapping

How does Gene Mapping Work?

Gene mapping involves identifying gene locations on chromosomes using methods such as linkage analysis, physical mapping, and sequencing, which helps in the study of genetic traits and diseases.

Give an Overview of Gene Mapping.

Gene mapping refers to the techniques used to determine the location of genes on a chromosome and can be done by physical linkage mapping and genetic linkage mapping.

What are the Techniques used in Gene Mapping?

Various techniques are used in gene mapping, like gene marker analysis of RFLPs, SNPs, GWAS, FISH, and genome sequencing.

What are the Limitations of Gene Mapping?

The limitation of gene mapping is the handling of large amounts of data and the unknown function of many genes in an organism, making it difficult to be mapped.

What is the Difference Between Gene Mapping and Gene Sequencing?

Gene mapping is the method of understanding the location of genes, while gene sequencing is the process in which the sequence of amino acids is determined on a chromosome.

What is Gene Maping in Bacteria ?

Gene mapping in bacteria involves identifying and locating genes on the bacterial chromosome, helping in understanding gene function and genetic relationships within bacterial populations.

Name the Two Types of Gene Mapping.

The two types of gene mapping are Genetic Mapping, which identifies the relative positions of genes on a chromosome, and Physical Mapping, which determines the actual physical distances between genes on a chromosome.

What is DNA Mapping?

DNA mapping is the process of determining the exact sequence of nucleotides in a DNA molecule which provides information about the genetic makeup of an organism, including the location of genes, regulatory elements, and variations within the DNA sequence.

What is the Difference Between Gene Mapping and DNA Sequencing?

Gene mapping involves identifying the locations of genes on chromosomes and determining their relative positions, while DNA sequencing involves determining the exact sequence of nucleotides in a DNA molecule.

What are the Different Types of Genome Mapping?

Different types of genome mapping include genetic mapping, which locates genes on chromosomes, physical mapping, which measures the distances between genes, and comparative mapping, which compares genomes across species.