Genetic Viological Markers, Cytological Markers And Biochemical Markerss?

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The traditional genetic analysis within populations by morphological markers, cytological markers and biochemical markers has not been very efficient when the selection objective involves several characteristics with unfavorable genetic correlation (Schwerin et al., 1995). These complications might include interactions between genes in the same locus (dominance) or in different loci (epitasis) or between specific genes and the environment (genotype by environment interactions) (Drinkwater et al., 1991). Also, the important phenotypic traits like rate of survival are expressed very late in the life to serve as useful criteria of selection (Dodds et al., 1996). To overcome this phenotype based genetic markers problem led to the …show more content…

A molecular marker may be a short DNA sequence such as a sequence surrounding a single base-pair change like single nucleotide polymorphism (SNP) or a long one like minisatellites (Jeffreys et al., 1985) and microsatellites (Jarne and Lagoda, 1996). That leads to the development of a new type of marker that is single nucleotide polymorphism (SNP) (He et al., 2003). However, AFLP markers are devoid of dense marker maps, so still used for QTL mapping and genetic diversity studies in species (Nicholas, 1997; Van Haeringen et al., 2001). With time the RFLPs was replaced by microsatellites for building genetic maps in human and animal species. Factor responsible for development of microsatellites are firstly, at a single microsatellite locus large number of alleles are found thereby, developing a high heterozygosity values enabling to reduce the number of reference families to be used for building the map and secondly, the possibility to perform genotypes by simple PCR followed by allele sizing on polyacrylamide gels (Dinesh et al., 1995). Some points should be taken into consideration when using molecular markers for genetic studies. As for molecular biologists the genotyping procedure should be simple and cheap in order to generate the vast amount of genotyping data as often necessary. From the statistician's angle some characteristics are most important like the dominance relationships, information content, neutrality, map positions or genetic

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