Although the capture and trading of great apes has been banned in 112 countries since 1973, it is estimated that about 1000 chimpanzees are removed annually from Africa and smuggled into Europe, the United States, and Japan. This illegal trade is often disguised by simulating births in captivity. Until recently, genetic identity tests to uncover these illegal activities were not used because of the lack of highly polymorphic markers (markers that vary from one individual to the next) and the difficulties of obtaining chimpanzee blood samples. A study was reported in which DNA samples were extracted from freshly plucked chimpanzee hair roots and used as templates for PCR. The primers used in these studies flank highly polymorphic sites in human DNA that result from variable numbers of tandem nucleotide repeats. Several offspring and their putative parents were tested to determine whether the offspring were 'legitimate' or the product of illegal trading. The data are shown in the following Southern blot.

Examine the data carefully and choose the best conclusion.
a. None of the offspring is legitimate.
b. Offspring B and C are not the products of these parents and were probably purchased on the illegal market. The data are consistent with offspring A being legitimate.
c. Offspring A and B are products of the parents shown, but C is not and was therefore probably purchased on the illegal market.
d. There are not enough data to draw any conclusions. Additional polymorphic sites should be examined.
e. No conclusion can be drawn because 'human' primers were used.

Verified step by step guidance

1. Understand the context: The problem involves using DNA polymorphic markers (variable number tandem repeats, VNTRs) amplified by PCR to verify parentage of chimpanzee offspring, similar to human forensic or paternity testing.
2. Recall the principle of inheritance for VNTR markers: Each offspring inherits one allele from each parent at a given locus, so the offspring's band pattern should be a combination of bands present in the mother and father.
3. Analyze the Southern blot data by comparing the band patterns of each offspring with those of the putative parents. For each offspring, check if every band can be accounted for by at least one parent’s band.
4. Determine legitimacy: If an offspring has bands not present in either parent, it suggests that the offspring is not genetically related to those parents and may have been illegally traded or purchased.
5. Evaluate the options based on your analysis of the band patterns and inheritance rules, considering whether the data are sufficient or if additional markers are needed to confirm parentage conclusively.

Key Concepts

Variable Number Tandem Repeats (VNTRs)

VNTRs are DNA regions where a short nucleotide sequence is repeated a variable number of times among individuals. These highly polymorphic markers are useful for genetic fingerprinting because the number of repeats differs between individuals, allowing for identification and parentage testing.

Polymerase Chain Reaction (PCR) and Primer Specificity

PCR is a technique used to amplify specific DNA sequences using primers that flank the target region. Using primers designed for human VNTRs can still amplify similar regions in closely related species like chimpanzees due to genetic similarity, enabling analysis despite cross-species primer use.

Parentage Testing Using Genetic Markers

Parentage testing compares genetic markers between offspring and putative parents to verify biological relationships. Offspring inherit one allele from each parent at polymorphic loci, so mismatches at these loci can indicate non-parentage or illegal trade in animals.