Analyzing Genetic VariationA Paternity Case |
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About This ActivityThis activity simulates a paternity case. Students analyze DNA typing data to determine whether I. M. Megabucks, a recently deceased megabillionaire, is actually the father of any of three children alleged to be his heirs. Students should have completed Analyzing Genetic Variation: DNA Typing (chapter 24) before doing this activity unless you are doing this lesson with younger students. For modifications for younger students, see below under Procedure. Younger students should have recently completed Generating Genetic Variation: the Meiosis Game (chapter 23; the crossing-over exercise is not necessary). They also need to have completed DNA Scissors (chapter 10), so that they understand what a restriction enzyme does. Please refer to the introductions to Generating Genetic Variation: the Meiosis Game and Analyzing Genetic Variation: DNA Typing for background.Class periods required: 1 IntroductionDNA-based paternity determinations are carried out by biotechnology companies such as Genetic Design, Inc., of Greensboro, N.C. The standard method is to analyze samples from the mother, the child, and the alleged father. Occasionally, however, the alleged father is deceased and did not (unlike Megabucks) prudently leave behind a blood sample for future DNA typing needs. In these cases, biotechnologists type DNA from known relatives of the alleged father, such as his acknowledged children or his parents. The DNA profiles are compared. Since two people who share the same father will have many more bands in common than two randomly selected individuals, it is possible, with careful analysis, to determine paternity on the basis of DNA profiles from a man's close relatives.A particularly poignant application of DNA testing occurred in Argentina. During the Argentine military's brutal rule (1976 through 1983), many families were torn apart. Often, parents were murdered, and their children were given away or sold. In other cases, parents were dragged away to prison, unwillingly leaving their babies to uncertain fates. Now that Argentina has a new government, the relatives of these kidnapped or disappeared children are trying desperately to find them. Many of the relatives are women whose children were murdered and who are now seeking their missing grandchildren. DNA testing has established the identities of dozens of formerly missing children, allowing them to be reunited with their relatives. "Genes of War" (Discover, October 1990, p. 46Ð52) is a story about the work of Dr. Mary-Claire King, the scientist who has been instrumental in helping the Argentinian families find their lost relatives. |
Dr. King used mitochondrial DNA (see the introduction to chapter 24) in her analyses. Because the parents of the lost children had often been murdered, DNA from more distant suspected relatives was usually the only evidence available for comparison. Since mitochondrial DNA is passed on through the females in a family lineage, a child's mitochondrial DNA profile exactly matches the profile from her mother's mother, all of her mother's siblings, and the children of her mother's sisters. Note: The activity in this chapter does not involve mitochondrial DNA. ObjectiveAfter completing this activity, students should be able to explain the process of analyzing DNA data to determine whether a particular man is the father of a child.MaterialsPhotocopies of the Student Activity pages if students do not have manualsPreparationMake photocopies, if necessary.ProcedureThis activity is self-explanatory. Students analyze the data on the worksheet. Your posters of human chromosomes from the meiosis game (chapter 23) will be helpful if you need to reinforce the idea that half of a person's chromosomes came from the mother and the other half came from the father. The posters will also illustrate that not all of the DNA bands seen in the typing data from the mother or the father would be in the child's DNA (fully half of each parent's DNA is not represented in the offspring's DNA).AnswerY's child could be Megabucks' child.Question for DiscussionWhy are the number of bands from the mother and the number from the father different in different children?The difference is a consequence of variations in the DNA sequences. As restriction sites are created and destroyed by changes in base sequences, the number of restriction fragments in the region that hybridizes to a probe also changes. See the activity about Bob's and Mary's chromosome 19s in Analyzing Genetic Variation: DNA Typing (chapter 24) for an example. |