Question

1)Discuss how single nucleotide polymorphisms/mutations can be analysed and utilised in forensic science. please write approx 700 words

Answer 1

INTRODUCTION- Single Nucleotide Polymorphism is abbreviated as SNP and is responsible for the genetic variation among populatio. Each SNP represents a difference in single nucleotide. They are present throughout the information of a person. SNP acts lke a genetic marker that helps scientists to diagnose a genetic abberaion or an abnormality. When the SNPs are present within the genr or in its vicinity, they play a direct role in causing a genetic disease by altering the gene functioning. SNPs are the polymorphisms that are the result of the point mutation which causes the generation of new nucleotide bases by altering the previous ones withing a locus of a gene. Since there are plethora of SNPs in the genome, so they directly acts as a biological marker. Various techniques of bioinformatics and sequencing are studied and applied for the identification.

METHODS FOR ANALYSING SNPs:

1. SNP MICROARRAY- In this technique, many probes are arranged on a small chip which allows large amounts of SNP to be integrated at the same time and place. Since SNP nucletides merely varies by one nucleotide and it is practically not possible to form hybridization conditions for all the probes, so, the target molecule of DNA has a capability to anneal with the mismatched probe molecule. Probes are designed in such a way so that they have a SNP site at different locations and it also contains mismatched SNPalleles. On comparing the different amounts of hybridizations of the target DNA molecule, it becomes feasible to determine hetrozygous or homozygous alleles.

2.RFLP (RESTRICTION FRAGMENT LENGTH POLYMORPHISM)- This technique involves the use of restriction endonuclease enzymes that has an ability to have high affinity for unique and specific restriction site. Genomic sample is subjected to enzymatic digestion and the fragments are separated by electrophoresis. By analysing the size of the sparated fragments it is possible to identify whether the restriction site has been cut by the enzyme or not. If that fails to happen, this implies that there is a mutation at the point of restriction site which has altered the nuclease activity.

3.OLIGONUCLEOTIDE LIGATION ASSAY- DNA ligass is responsible for catalysing the ligation in 3' to 5' direction, so, this mechanism is used to interrogating SNP by hybriding 2 probes over the polymorphic site. As a result, ligation can take place if the probes are complimentary to the DNA molecule . In this technique, a probe specific to allele hybridises with the DNa at 3' site which is over the SNP nucleotide. Second probe hybridises in the downstream direction of SNP polymorphic siteand it thus provides 5' site for the ligation activity. If allele specific probe exactly matches with the DNA sequence, only then the ligation will occur. Whereas, no ligation will take place where there is a mismatch 3' base. After that, ligated and non-ligated products ate separated and analysed by gel electrophoresis.By this way, high-throughput sequences data is generated by the ligated products and hence the genotype is determined.

UTILIZATION IN FORENSIC SCIENCE: Nowadays, there is an increase in the interest in the science behinf SNP, especially in the forensic science. SNP is vividly applied for defining the structure of Y chromosome or mitochondrial DNA and maternal inheritence or geographical analysis and origin of the samples. These days forensic researchers are involved in the determination of the autosomal SNPs due to their advantage in paternity testing as they have lower mutation rates and involves the use of short amplicons.

SNP can be used to match the forensic DNA to that of the DNA from the suspect and further to be used in DNA fingerprinting technique. It can be used to distinguish for the phenotypic clues such as color of the eyes, hair pattern, ethnicity, etc.

There arises some situations where there is a lower amount of forensic sample or a degraded sample, then the SNP methodologies serve as a good alternative as it has plethora of potential markers and the potential reduction of fragment length is merely 70-80 base pairs. SNP can be therefore useful in forensics in the case of murder, parental disputes, suspect identification in the case of rapes, etc.