DNA fingerprinting is a technology that identifies particular individuals using properties of their DNA It is also termed DNA profiling Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 19.4 DNA FINGERPRINTING 19-62

When subjected to DNA fingerprinting, chromosomal DNA gives rise to a series of bands on a gel The order of bands is an individual’s DNA fingerprint It is the unique pattern of these bands that makes it possible to distinguish individuals Certain loci in human chromosomes are variable in length These loci contain tandemly repeated sequences called minisatellites Variable Number of Tandem Repeats (VNTRs) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 19-63

19-64 Figure Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display VNTRs Restriction enzyme sites DNA probes are used to hybridize specifically to the repeat sequence located within VNTRs

Figure Protocol for DNA fingerprinting 19-65

19-66 Figure Protocol for DNA fingerprinting The probe is called a multilocus probe (MLS) It binds to ~ 20 to 40 fragments of DNA that contain the sequence

Mixed probes A+B

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA fingerprints from a murder case Defendant’s blood (D) Blood from defendant’s clothes Victim’s blood (V) D Jeans shirt V 4  g 8  g

RFLPs as markers for disease- causing alleles RFLP marker DNA Disease-causing allele Normal allele

In the past decade, the technique of DNA fingerprinting has become automated It is now done using PCR, which amplifies short tandem repeat sequences (STRs) Like VNTRs, STRs are found in multiple sites in human genomes and are variable among different individuals The main difference between a VNTR and STR is size STRs are much shorter, usually 100–450 bp STRs are called microsatellites, and VNTRs minisatellites The amplified STRs are fluorescently labeled They are separated by gel electrophoresis A laser excites the fluorescent molecule within the STR A detector records the amount of emission for each STR Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 19-67

19-68 Figure Protocol for DNA fingerprinting Each peak has a characteristic mass The pattern of peaks is an individual’s DNA fingerprint Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Within the past decade, the uses of DNA fingerprinting have expanded in many ways In medicine, it is used identify different species of bacteria and fungi and also different strains of the same species This is useful for appropriate antibiotic treatment DNA fingerprinting is also used in forensics and relationship testing Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Uses of DNA Fingerprinting 19-69

19-71 Figure The use of DNA fingerprinting to establish paternity Male 2 does not have many of the child’s paternal bands Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Therefore he cannot be the biological father Male 1 has all the child’s paternal bands The probability of this occurring by chance alone is very small Therefore he is the biological father