Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

You learned in the chapter that an STR locus is a locus where alleles differ in the number of copies of a short, tandemly repeated DNA sequence. PCR is used to determine the number of alleles present, as shown by the size of the DNA fragment amplified. In the Figure below are the results of PCR analysis for STR alleles at a locus where the repeat unit length is 9 bp, and alleles are known that have 5 to 11 copies of the repeat. Given the STR alleles present in the adults, state whether each of the four juveniles could or could not be an off-spring of those two adults. Explain your answers.


Summary Introduction

To explain:

STR (short tandem repeat) is the locus where there is a difference in the alleles in context of the number of copies of short, repeated sequences of DNA (deoxyribonucleic acid). The process of PCR (polymerase chain reaction) is used to detect the number of alleles with the help of the size of the DNA fragments amplified. The figure indicates the results of the PCR experiment for the STR alleles of a locus, in which the repeat unit length is 9 bp (base pair) and the alleles have 11 copies of the repeat. The adults have STR alleles, and whether all of the four juveniles are offsprings of these two adults.



The short tandem repeat (STR) is a microsatellite (a segment of repetitive DNA containing the DNA motifs). The analysis of the STRs gives the exact number of repetitive units. It is an important tool in forensic science that recognizes particular STR regions found in nuclear DNA.


A male adult has a DNA fragment of 72 and 54 bp, whereas a female adult possesses a DNA fragment of length 99 and 54 bp. The sizes of the DNA fragments are to be matched between the adults and the juveniles. When the size of one of the DNA fragments of the juvenile matches with one of the adults (male) and the other (female) matches with another adult, the juvenile must be the offspring of the two adults.

The first juvenile has one DNA fragment of 72 bp and another one of 81 bp. The first DNA fragment size matches with the male’s DNA fragment, but the second DNA fragment size matches neither of the adults. Thus, it can be deduced that juvenile 1 is not an offspring of these two adults.

The second juvenile has a broad band of DNA, which means that there are two fragments of DNA and both are of the same size, that is, 54 bp...

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