- repeating sequences of DNA (such as the sequence 5’ CATCATCATCAT 3’)

Variable number tandem repeats (VNTRs)

- are repeating sequences of DNA that vary in their number of repeating units between individuals

- VNTRs can be used to differentiate between the DNA of individuals in a process known as DNA fingerprinting. • In a typical DNA fingerprint, several VNTR markers are compared in order to decrease the odds that more than one person will have identical DNA fingerprints. - A sample of blood is extracted from a glove at a crime scene and placed in a test tube. - A specific variable number tandem repeat (VNTR) sequence is amplified using the polymerase chain reaction technique. - A sample of blood is taken from the two suspects (you and George). The same VNTR that was amplified from blood at the crime scene is amplified in each of the suspect’s samples. - George’s VNTR has 12 repeating units, while your sample has 3 repeating units. - Each of the amplified VNTR samples is separated using gel electrophoresis. Remember: small DNA molecules move more quickly in the gel than large DNA molecules; thus, small molecules will travel farther in the gel within a given period of time. - It looks like George is a match! But George isn’t guilty yet! A single VNTR is not typically sufficient to prove anything because the odds that two people have the same VNTR can be relatively high (for example, one in forty). - Several VNTR’s must be compared in order to reduce the odds that two people will have the same fingerprint. For example, if the odds of two people having the same VNTR were one in forty and remained constant, the odds of two people having six identical VNTRs would be one in 4,096,000,000 (1/40 x 1/40 x 1/40 x 1/40 x 1/40 x 1/40)! - If after several VNTRs have been compared and George’s DNA matches, then the chances are remarkably high that it was George’s blood on the glove. See you later George!

Variable number tandem repeats can be used for DNA fingerprinting because

- the exact number of repeats within a particular stretch of tandem repeats varies widely in a population. - variations in the number of repeats can affect the length of restriction fragments.

Tandemly repetitive DNA is composed of

- short sequences of DNA that are adjacently repeated

7.3.3 DNA Fingerprinting Flashcards by Irina Soloshenko

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7.3.3 DNA Fingerprinting Flashcards

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