EXERCISE III: ation Forensics Questions 13-17. of people. STR alleles, like othe
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EXERCISE III: ation Forensics Questions 13-17. of people. STR alleles, like other alleles, occur at different frequencies in different population Lets say that you have analyzed DNA samples from unrelated persons for 4 an STR locus alleles 3, and have placed them in groups based on their genotype. This obtained each genotype and the 4, and 5). The picture below shows the gel patterns that were for number of people you found for each (numbers across the top). Use this image to answer questions 13-17. Number of people with each genotype 9 21 12 15 18 6 6 7 5 1 Wells 13. Why do most lanes show two bands? 14. How is it possible that some people only show one band? 15. Calculate the frequency of alleles 3 and 4. Show your work. (Hint: Count the number of alleles 3 and 4 in the population and divide by the total number of all alleles in the population. The number above each well lists the number of people in the population with that specific genotype.) Page 7 of 8Explanation / Answer
13. After short tandem analysis(STR) of alleles of genes on chromosomes it is analysed from bands obtained after agarose gel electrophoresis that presence of two bands on the gel is due to the presence of two alleles of gene present on the same chromsome locus in patient samples obtained after PCR amplification.
14.The presence of one band in agarose gel electrophoresis after STR is due to the presence of one amplification of only one allele for a gene present on the chromosome locus in patient samples.
15.allele frequency= number of alleles of gene 3 and 4/total number of alleles in all patient samples
allele frequency=102/172 =0.5930.
16.allele frequency of allele 3=44/172=0.255
allele frequency of allele 4=58/172=0.337.
match probability(PM)= (allele frequency of 3)2 or (allele frequency of 4)2.
match probability of gene 3(PM)=(0.255)2=0.0650.
match probability of gene 4(PM)=(0.337)2= 0.1135.
power of discrimination of allele 3=1-PM of allele 3=1-0.0650=0.935--answer
power of discrimination of allele 4=1-PM of allele 4=1-0.1135=0.8865-answer.
power of discrimination of allele 3 is more than that of allele 4 in thief patient samples.
17.The genotype of the thief for power of discrimination to be greatest should be for allele 2 with power of discrimination value=1-(19/172)2 = 1- (0.110)2= 1-0.0121=0.9879-ANSWER.
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