5. Polyacrylamide gel electrophoresis is used to resolve VNTR polymorphisms in i
ID: 92141 • Letter: 5
Question
5. Polyacrylamide gel electrophoresis is used to resolve VNTR polymorphisms in identity testing. The following diagram shows the pMCT118 genotypes for 6 individuals. The marker lanes (Ladder) show most of the known pMCT118 alleles, each differing by one repeat unit. A person’s genotype is “scored” by comparing the bands in the genotype to those in the marker lane. For example, person #1 has one 35-repeat allele and one 36-repeat allele, and is scored as 35, 36.
a. Score the remaining individuals. Round to the closest whole number. (2 pts)
b. What percentage of individuals (from the 6 individuals mentioned above) are heterozygous-having two different alleles? (1 pt)
c. Using the gel and chart given, which alleles appear to be most common? (1 pt)
d. The sizes of the PCR products of the D1S80 locus in one family were 360 and 420 bp in the mother and 515 and 704 bp in the father. What are all possible fingerprints their children could have? (1 pt)
Allele Frequency (n-number of alleles typed) US African Caucasians m214 0.05 0.265 0.079 0.005 0.005 0.045 0.033 0.010 0.108 0.030 0.108 0.005 0.028 0.320 0.168 0.045 0.014 0.025 0.009 0.010 0.005 0.050 0.17 0.075 0.05 0.005 0.060 0.06 0.015 0.005 0.005 0.005 0.089 0.005 0.005 0.015 0.005 0.005 0.005 Hispanic Americans 0.005 0.28 0.014 0.033 0.029 0.005 0.300 0.038 0.010 0.010 0.038 0.062 0.07 0.062 0.005 0.010 0.005 0.010 0.010 0.005Explanation / Answer
VNTR (Variable Number Tandem Repeat) are the locations in genome where short DNA sequences are arranged in tandem repeats.
They are interspersed through out the genome. They are present in many chromosomes and the variants are inherited alleles. Thus they are used in genetics, evolution and forensic research.
VNTR are the minisatellites with the sequence repeats of 10 to 100 base pairs, in contrast to the microsatellites, which are 2 to 5 base pair repeats.
The number of repeated units vary amongst individuals.
Multilocus VNTR analysis is the usual method of molecular typing.
VNTR exhibits a range of copy numbers.
VNTRs are selected and primers are designed against the flanking regions of tandem repeats.
Thus the size of the base pairs is the sum of size of the tandom repeats and the size of the flnking region on both sides.
Amplicon size = Size of the forward flanking region + size of reverse flanking region = (Size of the tandem repeat X Repeat copy number)
VNTRs are characterized using Southern hybridization. Both the flanking regions are cut using restriction digestion (Restriction endonucleases).
Analysis of VNTR by southern hybridization usually results in a two band pattern, each band inherited from each parent. A one band pattern appears if the size of the two parental bands are same.
Each individual can be analysed for all the markers but it is practically difficult to analyze hundreds of markers. Fully automated Computer programs are designed which help in multi locus VNTR analysis.
The allele frequency represents the measure of the relative frequency of an allele at a particular locus in a given population.
The allele frequency of a particular allele is calculated usinf the formula:
Frequency of an allele X = Number of copies of allele X in population/ Total number of copies of gene in population
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