DNA Detective: Reuniting Families with DNA Fingerprinting and Electrophoresis
Determined to learn more, they turned to the elders of their community, hoping for answers. The elders informed them that one of their fathers had passed away, while the other was still alive but suffered from memory loss due to an accident. As for their mothers, the two women believed to be their biological parents were located in a rehabilitation facility. The facility housed nearly 200 women, many of whom had been displaced. Based on age and appearance, about ten women fit the possible profile of their mothers. DETERMINATION OF PARENTAGE USING DNA FINGERPRINTING First, the boys sought to determine which of the ten women were their mothers by performing mitochondrial DNA fingerprinting. Mitochondria, the “powerhouse” of the cell, are unique organelles in that they contain a small DNA genome. This genome is useful for identifying maternity because mitochondria are inherited through the female line. Before conception, a human egg contains a large number of mitochondria. In contrast, human sperm contains very few mitochondria. Upon fertilization of the human egg by a sperm, the developing zygote contains mitochon- dria obtained from the mother’s egg. Mitochondrial DNA fingerprinting tests can be used as an initial screening technique because they are less expensive than chromosomal DNA testing and results are available in a shorter period of time. In this case, since the boys were cousins (their mothers were half-sisters who shared the same mother), the mitochondrial testing results would be identical for the two boys. The tests did identify two women with mitochondrial DNA fingerprinting patterns that matched that of the boys! Now, in order to match the boys with the correct parents, chromosomal DNA fingerprinting tests were ordered for the boys, the two mothers, and the surviving father. Chromosomal DNA, which is present in the nucleus of every living cell, is the genetic material that acts as a blueprint for all of the proteins synthesized by that cell. Unlike mitochondrial DNA, chromosomal DNA is an equal composite of both parents. In each chromosome pair, one is inherited from the father and the second from the mother. Although most of this DNA is identical between individuals, small sequence differences, or “polymorphisms”, occur at specific locations throughout the genome. These polymorphisms include single base pair changes and repetitive DNA elements. By examining several of these polymorphic regions, we can generate a unique “DNA fingerprint” for that person. DNA fingerprints can allow us to distinguish one individual from another. Because polymorphisms are inherited, DNA fingerprints can also be used to determine pater - nity/maternity (and other familial relationships). In this experiment, to determine parentage, the DNA fingerprints of the boys are compared with the DNA finger - prints from the surviving father and the two mothers. Since chromosomal DNA is inherited from both parents, the DNA fingerprint of a child will contain a mixture of polymorphisms from each parent. By analyzing DNA bands on a gel, students will uncover how forensic genetics can reunite families and solve real-life mysteries.
3
1.800.EDVOTEK • www.edvotek.com • info@edvotek.com
Made with FlippingBook flipbook maker