Introductory Chapter: Assessment and Conservation of Genetic Diversity in Plant Species

2.1. Storage proteins

One important output of post-transcription and translation processes is the protein, which represents the genetic DNA as well as the structural and enzymatic material of an organism’s cells [2]. Genetic divergence is found to have impacts on proteins. For example, seed proteins that are of essential roles in species are tolerant to environmental occurrences. Recent approaches have employed several technologies to identify the characteristics of various plant cultivars and genotypes [2]. One quickly and precisely technology utilized for such purpose is electrophoresis. The genetic divergence was assessed within Lathyrus sativus through accurate electrophoretic analysis of its seed storage proteins [2, 7], suggesting its fundamental role in evaluating the relationship between taxonomy and genetics at and below the species level [2].

2.2. Isozyme markers

Isozymes, also called isoenzymes, are proteins exhibiting same catalytic and quantitative function as the enzyme but, meanwhile, they differ in their molecular forms [2]. Various alleles within a single locus are encoded by structural genes to give the allozyme, an allelic variant of the enzyme. Biological analysis of isozymes reveals significant importance, including the assessment of genetic divergence as well as phylogenetic and taxonomic relationships [2]. It also helps to investigate population genetics and developmental biology as well as to conserve the genetic resources of plants [8, 9].

3.1. Restriction fragment length polymorphism (RFLP)

RFLP is a dominant marker that involves breakages of DNA bonds at specific nucleotides by the action of enzymes called restriction endonucleases [8, 10], followed by size fractionation of digested fragments by electrophoresis technique, suggesting for these markers a key role in setting up genetic mapping as well as evaluating genetic diversity and phylogenetic relationships. RFLP markers could be a possible option to identify the characteristics of individuals, to estimate segregational analysis of progenitors as well as to evaluate genetic variation and phylogenetic relationships in the germplasms of lettuce plants, but these techniques proven to be expensive, technically complicated, and away from optimal performance [10]. Therefore, research is needed to develop low cost and more efficient molecular genetic technologies to inhibit or even limit the technical obstacles related to RFLP technique and to study the properties of genetic difference within plants [10].

3.2. Random amplified polymorphic DNA (RAPD)

RAPD, a PCR-based technique or (AP-PCR), involves the use of arbitrary short primers [8, 10] in a PCR reaction to amplify random sequences from DNA template. RAPD has proven to be a multipurpose technique utilized for constructing genetic map [11, 12], utilization in breeding approaches [13], identification of resistant genes and hybrid origin [14], and for assessing plant genetic variance by characterizing differences between populations of the similar germplasm resources [11, 12].

3.3. Amplified fragment length polymorphism (AFLP)

AFLP is a highly reproducible marker that utilizes PCR technique to amplify DNA fragments [8, 10]. It is a DNA fingerprinting-based technique that includes digestion of DNA into small fragments with the help of restriction enzymes. These fragments are ligated by adaptors complementary to their restriction sites followed by selective amplification of the newly formed subset by PCR technique [10]. Autoradiographic and fluorescence technologies are then utilized to visualize the amplified fragments on polyacrylamide gels. AFLP is proven its successful participation in identifying the characteristics of genetic diversity and relationships of plant species [8, 10, 15, 16, 17, 18, 19, 20].

3.4. Microsatellites (SSRs)

Microsatellites are repetitive sequences of nitrogen bases within DNA. These repeats may be mono-, di-, tri-, tetra-, or penta-nucleotides found in eukaryotic nuclear genome [8, 10]. Microsatellites are genetically different. Therefore, they are employed in estimating genetic divergence and recognizing the relationships between plant genotypes [10, 21].

In conclusion, morphological, cytological, biochemical, and molecular markers proved useful in assessing genetic diversity levels in different plant species [22, 23, 24, 25, 26, 27, 28, 29, 30].