Quiz 8: Dna Fingerprinting and Forensic Analysis
The term "poly" means "many" and "morphic" refers to "shape," so the term "polymorphic" refers to many shapes. Polymorphic DNA sequences vary among individuals. However, there are certain DNA stretches that do not vary among individuals; therefore, they are not used in analytical methods for finding differences among individuals. They are the forms of alleles that are present in a chromosomal locus in such a way that they differ gradually in their gene sequence or may possess repeated nucleotide sequence. Polymorphic DNA is used to distinguish individuals, as they vary among organisms. Polymorphic DNA is analyzed by the use of RAPD (random amplification of polymorphic DNA) technique.
The polymorphic DNA sequences vary among individuals. They are the forms of alleles which are present in chromosomal locus in such a way that they differ gradually in their gene sequence or may possess repeated nucleotide sequence. Polymorphic DNA is used to distinguish individuals as they vary among organisms. STR stands for " short tandem repeat "; it is a short stretch of repeated DNA sequence. These are also known as " microsatellites ". The polymorphic DNA sequences which have been analyzed in DNA fingerprinting do not show any effect on the individual. This is because it occurs in those regions of DNA which are not translated into protein.
Short Tandem Repeats (STR) analysis is the tool used to compare the specific loci on the DNA from more than two samples. This assay is generally performed in forensic case studies and in paternity tests. Generally these STRs are short DNA sequences which are 2-5 base pair length. This assay works on the same principle to that of RFLP (restriction fragment length polymorphism), but differs only that in this case the DNA is not treated with restriction enzymes. So this technique is more advanced than RFLP. Here the DNA is probed and then PCR (polymerase chain reaction) is performed. Thus amplified DNA is subjected for autoradiography. When STR analysis of a child is performed, then we notice half of the child's DNA is from mother and the other half is from the father.