Introduction
Gene mapping is an investigation method that allows determining genes’ loci on chromosomes and distances between them. As a result, a full genome map or a map of a particular chromosome can be obtained. Gene mapping started to develop at the beginning of the 20th century (Nimbalkar et al. 5). In the middle of the century, new molecular biology methods, in particular, DNA sequencing, appeared, and the efficiency of gene mapping significantly increased. This technique elucidates genes’ functions, regulatory mechanisms, heredity, and variability and provides significant genetic information for different studies (Kumar et al. 7). Nowadays, two different methods of gene mapping (genetic mapping and physical mapping) exist, and both of them are used in various genetic investigations, in particular, in biomedical and plant researches.
Types of Gene Mapping
All the inherited information is coded into genes. Genes consist of DNA or, in the case of some viruses, RNA. Genes are organized into chromosomes, and each one has a particular place on them. Gene mapping is the basis for generic investigations because it allows determining each gene’s position on a chromosome and its connection with other genes. Two different techniques of gene mapping are used in scientific researches: genetic mapping and physical mapping (Nimbalkar et al. 5).
Genetic Mapping
Genetic mapping is based on the linkage between genes that are located on the same chromosome. This method was used for the first time at the beginning of the 20th century for the fruit fly. It was popular and widely used before new molecular technologies appeared (Nimbalkar et al. 6). Results of genetic mapping are approximate. Another problem with this method is that it allows mapping just genes but not the noncoding DNA. However, it is known that the major part of the genome consists of noncoding DNA such as regulatory elements, repeat sequences, transposons, and others (Hartwell et al. 479). This problem is especially essential for mapping genomes of vertebrates, in particular, humans due to the high level of the noncoding DNA presence in the genome (Nimbalkar et al. 6).
For genetic mapping, data of numerous crosses should be analyzed to determine the frequency of recombination and to calculate the distance between two genes. If genes are located close to each other on the same chromosome, they could be linked. In this case, the assortment of these genes is not independent. However, this pair of genes could be separated after recombination. The frequency of recombination correlates positively with the distance between two genes in a pair. Therefore, if this index is significantly lower than 50%, it could be claimed that two genes are linked (Hartwell et al. 134). To create a complete chromosome map, recombination frequency should be estimated for each pair of genes. After that, an approximate position of each one and relations between them could be determined (Hartwell et al. 135).
Physical Mapping
In contradiction to genetic mapping, physical mapping determines the actual distance between two genes’ loci. This distance is measured in the base pair (b.p.). Several methods of physical gene mapping were developed recently. Restriction mapping is one of them. This method consists of the DNA molecule restriction, fragments separation, determination, and, finally, fragments combining. In this technology, restriction enzymes are used for DNA fragmentation. These enzymes cut the molecule in particular loci. After cutting, fragments of the DNA are separated and examined independently. Electrophoresis is commonly used for DNA fragments separation. The principle of electrophoresis is that fragments with different molecular weights move at a different speed in the electric field (Nimbalkar et al. 8–9).
The approach of fluorescent in situ hybridization (FISH) could also be used for the physical mapping of a particular gene. For this investigation, specific DNA probes should be constructed. These probes hybridize with target DNA fragments. After that, metaphase chromosomes should be dried and denaturized on microscope slides. Optical microscopic methods are used for probe detection and its place on chromosome determination. FISH is a widely used method of gene mapping that could provide data of any particular gene’s position. However, it is essential to know a sequence of a target gene to construct a complementary probe (Nimbalkar et al. 9–10).
Modern molecular biology methods allow obtaining complete and precise data according to the sequence of both coding and noncoding DNA (Staňková et al. 1523). DNA sequencing technology is the most promising for gene mapping. DNA sequencing is a method of the primary nucleotide structure of a DNA molecule determination. The Sanger chain termination method, which was developed in 1977, is used for this approach (Hartwell et al. 362). This method is based on the specific terms of DNA in vitro synthesis. As a result, numerous oligonucleotides, complemented to the initial DNA molecule fragments, are obtained. After that, polymerase chain reaction and electrophoresis are used to amplify, separate, and investigate these oligonucleotides (Nimbalkar et al. 10). In recent times, this technique was developed, and now it allows reading the whole genomes of different living objects, including humans (Hartwell et al. 363).
Gene Mapping Significance
It is difficult to overestimate the importance of the gene mapping technique. Nowadays, gene maps of different important for humanity living objects were created. Gene mapping is used in biomedical studies, agricultural investigations, microbiology, anthropology, paleobiology (in particular, paleoanthropology), evolutionary researches, and many others fields (Hartwell et al. 363). Specific databases with results of different species genome sequences were created. Free access is provided for these data. Thus, scientists worldwide could use these data for further investigations (Kumar et al. 8).
The Gene mapping technique is essential for biomedical studies, in particular, for detecting genes that are responsible for complex diseases (Nimbalkar et al. 5). Recently, numerous genetic biomedical studies were performed. New molecular biology methods development provides an opportunity to understand the genetic basis for normal and pathological human states. Significant results in this area were obtained during the Human Genome Project and related studies. This project was finished in 2003, and a complete map of all human genes was created (Kumar et al. 7).
Besides, gene mapping could be used to understand the molecular mechanisms of a particular disease. To achieve this goal, sequence products and proteins of a normal and pathological gene should be compared (Nimbalkar et al. 5). Pharmacogenomics is another essential area of biomedical researches. It appeared and was developed during the recent decades after the Human Genome Project accomplishment. Pharmacogenomics is focused on the individual reaction to the medications use. This reaction depends on the human genome because genes are responsible for all metabolic paths. In the future, it might allow the determination of the individual drugs’ composition and concentration (Nimbalkar et al. 12–13).
Another highly important area of gene mapping use is agricultural plant investigations. Gene mapping provides the essential data according to the genes with the high economic importance sequence, localization, and linkage. In particular, crop genes, which are responsible for the high productivity and disease and negative climatic conditions resistance, were detected (Nimbalkar et al 13). This technique is used for plant pathogenic organisms’ investigations. Genes, which are responsible for different diseases, were identified and studied (Staňková et al. 1523). Another area of gene mapping using is the gene-modified organisms (GMO) construction. This relatively new biotechnological field started to develop in the 1970s. Nowadays, GMO agriculture is widely used all over the world due to its economic benefits (Martin et al. 3).
Conclusion
Gene mapping started to develop in the 20th century. At the beginning of the century, the method of genetic mapping was used to determine the relative distance between a pair of genes. This approach was important for genetic development and biomedical and plant studies. However, it has several limitations, in particular, results of gene mapping are approximate, and this technique allows mapping just the coding DNA sequences. Another method of gene mapping is physical mapping. This approach provides data according to the physical distance between small DNA sequences on the DNA molecule. Different molecular biology techniques are used for physical mapping: restriction mapping, fluorescence in situ hybridization, and DNA sequencing. The last one is the most significant and developed in recent decades. DNA sequencing provides data on the nucleotide sequence of a DNA or RNA molecule. It was used in different investigations, including the Human Genome Project. Gene mapping is widely applied in researches. It provides essential data, in particular, for biomedical and agricultural plant investigations.
Works Cited
Hartwell, Leland H., et al. Genetics: From Genes to Genomes. 5th ed., McGraw-Hill Higher Education, 2014.
Kumar, Satish, et al. “The Human Genome Project: Where Are We Now and Where Are We Going?” Genome Mapping and Genomics in Human and Non-Human Primates. Vol. 5, edited by Duggirala, Ravindranath, et al., Springer, 2015, pp. 7-31.
Martin, Hannah M., et al. “Analysis of GMO Food Products Companies: Financial Risks and Opportunities in the Global Agriculture Industry.” African Journal of Economic and Sustainable Development, vol. 6, no. 1, 2017, pp. 1-17.
Nimbalkar, Vikram, et al. “Gene Mapping: Basics, Techniques and Significance.” International Journal of Clinical and Biomedical Research, vol. 1, no. 1, 2015, pp. 5–14.
Staňková, Helena, et al. “BioNano Genome Mapping of Individual Chromosomes Supports Physical Mapping and Sequence Assembly in Complex Plant Genomes.” Plant biotechnology journal, vol. 14, 2015, pp. 1523-1531.