"Genetic Linkage Mapping in Fungi"

 

  Linkage map is a representation of the genome that shows the relative position and distance between the markers or genes along chromosomes. Linkage mapping is a basic tool for genomic research.¹ The relative distance in a linkage map is a  function of crossover frequency between pair of markers or genes in a diploid mapping population. This basis is extensively used in the development of linkage map in plants and animals but this cannot be used in fungi. In fungi, existence of haplo - diplontic life cycle and formation of haploid spores in fruiting bodies is a way to determine the recombination frequency and development of the linkage map.

            In fungi, tetrad analysis is a reliable procedure to construct the linkage maps. Tetrad analysis may be ordered (Neurospora, Sordaria) or unordered (Yeast, Chlamydomonas). Ordered tetrad analysis is used to calculate the distance between the gene and centromere and  is used to map loci with respect to centromere. In unordered tetrad analysis,the recombination fraction and distance between genes is accounted by considering frequency of non parentl ditypes and tetrad ascus type.¹

            The use of DNA markers in development of linkage maps has gained the importance in the past few decades.the 2:2 segregation of DNA markers in tetrad are considered for the construction of linkage map and QTL analysis.² Bioinformatics tools have provided a good scope for development of linkage maps using the softwares which makes the job easy. Some of the softwares used are MAPMAKER V 3.0, MAPRF, Joinmap, MSTMAP, THREaD Mapper, DGMAP, AntMap, Map manager QTX, MAP CHART 2.1.²

            Many studies have been carried out in which linkage map is used for identification of useful genes. Spores of edible mushroom Pleurotus pulmonarius causes respiratory disorders in humans and deposition of spores on mushroom also reduces marketing value. Hence an attempt was made to map mutant gene causing sporelessnes using AFLP markers. The two AFLP markers closely linked to sporeless mutant gene were found useful in developing sporeless strains.³

            To conclude, construction of genetic linkage maps in fungi constitutes a milestone to initiate forward genetics or map- based cloning studies. Renewal of this old genetic tool integrated with most recent technologies will help to understand the complex traits and also identify the useful genes associated with specific traits or phenotypes in future.²

 

REFERENCES

¹ PRANAV, K. AND USHA, M. 2022,  Life Sci. : Fund.  Pract.(8^th ed.). Pathfinder

²FOULONGNE ORIOL, M. 2012, Genetic linkage mapping in fungi: current state, applications, and future trends. Appl. Microbiol.  Biot. 95(4):891-904.

³OKUDA, Y., MURAKAMI, S. AND MATSUMOTO, T. 2009, A genetic linkage map of Pleurotus pulmonarius based on AFLP markers, and localization of the gene region for the sporeless mutation. Genome, 52(5): 438-446.