Restriction Fragment Length Polymorphism (RFLP) Analysis
The genetic variability at a particular locus (gene) due to even minor base changes can alter the pattern of restriction enzyme digestion fragments that can be generated. Pathogenic alterations to the genotypic can be due to deletions or insertions within the gene being analyzed or even single nucleotide substitutions that can create or delete a restriction enzyme recognition site. RFLP analysis takes advantage of this and utilizes Southern blotting of restriction enzyme digested genomic DNA to detect familial patterns of the fragments of a given gene, detectable by screening the Southern blot with a probe corresponding to the gene of interest. A classic example of a disease detectable by RFLP is sickle cell anemia.
Sickle cell anemia results (at the level of the gene) from a single nucleotide change (A --> T) at codon 6 within the b-globin gene. This alteration leads to a glu ----> val amino acid substitution, while at the same time abolishing a MstII restriction site. As a result a b-globin gene probe can be used to detect the different MstII restriction fragments. It should be recalled that there are two copies of each gene in all human cells, therefore, RFLP analysis detects both copies: the affected alelle and the unaffected allele.
Size variability in detectable fragments within a family pedigree indicate differences in the pattern of restriction sites within and around the gene being analyzed. RFLP patterns are inherited and segregate in Mendelian fashion thus, allowing their use in genotyping such as in cases of paternity dispute or in criminal investigations.
Another form of DNA polymorphism detectable by classical RFLP mapping results from the inherited variations in the number of tandemly repeated DNA sequence elements that are from 2 to 60 bp in length. The number of repeats is also variable from 2 to 40 copies. These elements are termed variable number tandem repeats (VNTRs). When restriction enzyme digestion cuts DNA flanking the VNTRs, the lengths of the resultant fragments will be variable depending upon the number of repeats at a given locus. Many different VNTR loci have been identified and are extremely useful for DNA fingerprint analysis such as in forensic and paternity identity cases.
Restriction Fragment Length Polymorphism (RFLP) AnalysisThe genetic variability at a particular locus (gene) due to even minor base changes can alter the pattern of restriction enzyme digestion fragments that can be generated. Pathogenic alterations to the genotypic can be due to deletions or insertions within the gene being analyzed or even single nucleotide substitutions that can create or delete a restriction enzyme recognition site. RFLP analysis takes advantage of this and utilizes Southern blotting of restriction enzyme digested genomic DNA to detect familial patterns of the fragments of a given gene, detectable by screening the Southern blot with a probe corresponding to the gene of interest. A classic example of a disease detectable by RFLP is sickle cell anemia.Sickle cell anemia results (at the level of the gene) from a single nucleotide change (A --> T) at codon 6 within the b-globin gene. This alteration leads to a glu ----> val amino acid substitution, while at the same time abolishing a MstII restriction site. As a result a b-globin gene probe can be used to detect the different MstII restriction fragments. It should be recalled that there are two copies of each gene in all human cells, therefore, RFLP analysis detects both copies: the affected alelle and the unaffected allele.Size variability in detectable fragments within a family pedigree indicate differences in the pattern of restriction sites within and around the gene being analyzed. RFLP patterns are inherited and segregate in Mendelian fashion thus, allowing their use in genotyping such as in cases of paternity dispute or in criminal investigations.Another form of DNA polymorphism detectable by classical RFLP mapping results from the inherited variations in the number of tandemly repeated DNA sequence elements that are from 2 to 60 bp in length. The number of repeats is also variable from 2 to 40 copies. These elements are termed variable number tandem repeats (VNTRs). When restriction enzyme digestion cuts DNA flanking the VNTRs, the lengths of the resultant fragments will be variable depending upon the number of repeats at a given locus. Many different VNTR loci have been identified and are extremely useful for DNA fingerprint analysis such as in forensic and paternity identity cases.
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