1. Analyzing DNA Fragments AP Biology Fall 2010

2. DNA Fingerprint  DNA fingerprint: unique array of base sequences in each organism that is slightly different from the DNA in other organisms Even close relatives

3. DNA Figerprinting  On some human chromosomes, there are sequences of repeated DNA (9 to 80 base pairs long). The number of repeats can vary from about one to thirty and are not the same from person to person. These sequences are called Variable Number of Tandem Repeats (VNTRs). Within the VNTRs there are sites where an enzyme can cut the DNA, and the location of these sites also varies from person to person. Cutting with the enzyme will lead to DNA fragments of different lengths, which are called Restriction Fragment Length Polymorphisms (RFLPs). These DNA fragments can be separated on an agarose gel based on their size. The RFLPs can be seen by probing using complementary radioactive DNA, and they are used to compare different samples of DNA.

4. DNA Fingerprinting  DNA fingerprinting can be used to identify a child’s parents. Each child inherits one set of chromosomes from each parent. This is why children resemble both of their parents. A child who has a mom with brown hair and blue eyes and a dad with blond hair and brown eyes might end up with brown hair from his mom and brown eyes from his dad. RFLPs are inherited in the same way, some from the mother and some from the father.

5. DNA Finerprinting  In this example, a family consists of a mom and dad, two daughters and two sons. The parents have one daughter and one son together, one daughter is from the mother’s previous marriage, and one son is adopted, sharing no genetic material with either parent. After amplifying the VNTR DNA from each member of the family, it is cut with a restriction enzyme and run on an agarose gel. Here are the results:

6. DNA Fingerprinting

7.  It is easy to see in this example that daughter 2 is the child from the mother’s previous marriage and son 2 is adopted. You can see that both daughter 1 and son 1 share RFLPs with both the mom and dad (coloured blue and yellow respectively), while daughter 2 has RFLPs of the mom but not the dad, and son 2 does not have RFLPs from either parent.  Even if the RFLPs were not colour coded, you could still distinguish the parents of the children by looking at the position of the bands in the agarose gel. In reality, all of the bands look the same and only the positions are different.

8. DNA Fingerprinting  DNA fingerprints can be used to determine the identity of a child’s parents if they are unknown. Generally, it is the father whose identity is in question, although in adoptions the biological mother’s identity could also be questioned years later. In the previous example, if the father of daughter 2 was alleged to be the dad in the example, DNA fingerprinting would prove that he is not, since none of his RFLPs line up with the daughters. DNA fingerprinting can also prove the identities of biological parents in the case of adoption.

9. DNA Fingerprint  The technique focuses on tandem repeats  Copies of the same short DNA sequences that are highly varied from one person to the next

10. DNA Fingerprint  The differences can be detected by gel electrophoresis  Technique that pulls molecules through a block of gelatin by electric current  Different size molecules travel at different speeds

11. DNA Fingerprint  The banding patterns of genomic DNA fragments are unique to each individual

12. DNA Fingerprint  DNA fingerprinting is now a widely accepted and valuable tool for forensic scientists to identify criminals, victims, and innocent suspects  http://www.pbs.org/wgbh/nova/sheppard /analyze.html http://www.pbs.org/wgbh/nova/sheppard /analyze.html