**4. Relationship between markers and use practices**

The markers presented are some similarities between themselves regarding the level of polymorphism, random distribution in the genome stability, gene expression among others. The comparison between them is presented in Table 2 adapted from Ferreira & Grattapaglia (1995).


Table 2. Comparative analysis for some characteristics of molecular markers.

The molecular markers reported so far in the chapter became important tools in the genetic improvement of plants. The following is a brief account made of the possible uses for these markers.

Construction of genetic maps: The Mendelian segregation observed in molecular markers, allows them to be used to construct genetic maps of connection and enable the location of genes within the chromosomes. QTLs mapping;

Characterization of genetic variability: the polymorphism generated from DNA and observed in the form of bands, allows us to study and confirm the genetic variability among plants;

Monitoring of genes: Genes may be screened in breeding programs that use the technique of backcrossing. Some applications of molecular markers linked to breeding programs can be facilitated through the use of this tool. In programs of backcross markers can maximize the efficiency of programs by increasing the probability of conversion of individuals and

Molecular Markers: Assisted Selection in Soybeans 173

Variations in the sequences are the result of mutations and SNPs are mutations that have spread over generations and may occur either in coding regions as in non-coding genomes. They are classified as non-synonymous when they occur in coding regions and can result in an amino acid substitution in the protein sequence. Classification as synonymous SNPs is given the changes that occur in non-coding region. These markers can be used in genotyping and as a new strategy for identification of polymorphism in species with low

Molecular markers are very important in structural and functional genomics of animal species, plants and microorganisms. The marker developed by Hu & Vick (2003) was named Region Amplification Polymorphism Target (TRAP). It's is a fast and efficient using bioinformatics tools and data from EST's to generate polymorphic markers around targeted candidate gene sequences based on PCR. It is considered a dominant marker, which

The polymorphism is generated from a combination of a fixed primer designed from an EST sequence of interest, and an arbitrary primer. Recent studies have reported the use of TRAP markers to access genetic diversity in sugarcane and identification of possible candidate genes for cold tolerance and metabolic pathway involved in sucrose (Alwala et al., 2006). The technique is extremely simply practice involving the extraction of genomic DNA and a

Möller (2010) evaluated 286 F2 plants from crosses of IAC-100 and CD-215 in order to identify markers linked to genes conferring resistance to sucking bugs of soybean seeds. For the marker TRAP, 11 primer combinations fixed / arbitrary generated 230 brands, and 31 (13.48%) polymorphic, an average of 2.82 marks per polymorphic combination. Despite the lower number of different polymorphic by combining the percentage of polymorphism

Finally the marker Nucleotide Binding Site (NBS) which has been successfully used in potato, tomato, lettuce, barley (Van der Linden et al., 2004), allowing the identification of areas of resistance genes highly conserved between species. The technique consists of amplification of specific regions using degenerate primers homologous to conserved

The visualization of fragments generated by molecular markers, is usually performed using gel electrophoresis, which can hinder the precise correlation between the bands and allelic variations. Technological developments put at the disposal of researchers, hybridization methods such as microarrays. The high cost restricts their use in most laboratories. Alternatively, we developed a methodology called: Diversity Arrays Technology (DArT),

The technique is based on the construction of panels of diversity and hybridization microarray. Its use allows the visualization of the presence or absence of specific fragments

Molecular markers have facilitated the studies of genetics, taxonomy and evolution of plants delivering breakthrough in scientific knowledge. New possibilities of genetic manipulation

The selection methods were largely enhanced by the use of molecular markers, and the success of marker-assisted selection depends on the degree of association between him and

which allows analysis of genomic representations without the need for sequencing.

combines the ease of the RAPD markers with polymorphism of AFLP markers.

obtained with the marker TRAP (0.13) was higher than for AFLP (0.10).

sequences of resistance genes (R-genes).

emerged, directly benefiting the plant breeding.

degree of polymorphism.

PCR reaction.

in the genome.

**6. Conclusion** 

reducing the time required to obtain an acceptable recovery of the recurrent parent (Borém & Miranda, 2005). The proportion of recurrent parent obtained in the first backcross generation, after selection of a marker in each of the chromosomes of tomato, roughly equals the proportion in three backcross generations in the absence of selection (Tankskey & Rick, 1980);

Genetic characterization: Description of a plant gene in their DNA. Molecular methods allow the varietal characterization with high discrimination power. Several studies have shown the quality of information on the molecular identification of germplasm (Lee et al.,1989; Smith & Smith, 1991).

Marker-assisted selection: The possibility of identifying genes of interest, to be strongly linked to molecular markers allows the selection can be made indirectly. In cases where gene expression occurs only in the final phase of the cycle of the species, such as the lipoxygenase in soybeans, the possibility of indirect selection through molecular markers becomes attractive (Borém & Miranda, 2005). The same authors reported useful for screening individuals who have two or more genes whose expression produces similar phenotypes, as is the case of pyramiding genes conferring resistance to a pathogen.

Great prospects for the area of molecular markers have been discussed. The potential usefulness of these techniques will be achieved, for example, through indirect selection based on markers: when the desired character has low heritability or present difficult evaluation, in situations where there are undesirable genetic correlations between traits, and especially the practice of early selection in crops perennials. The isolation, cloning and manipulation of individual genes that control quantitative traits of economic importance is a goal, theoretically attainable.
