A DNA profile is a pattern, usually shown as a series of bands or peaks, that represents the number of repeats a person has at several satellite DNA loci. Because the number of repeats varies so much between people, everyone except identical twins has a different DNA profile.Modern DNA profiles use short tandem repeats (STRs). At each locus a person has two alleles, one from each parent, so each locus gives one or two bands. In the UK, profiles are based on 16 STR loci plus a marker that shows whether the DNA is from a male or a female.Producing a DNA profile (an overview):
1. DNA is extracted from a sample such as blood, saliva, hair roots or skin cells.
2. PCR is used to amplify the STR regions. Primers are chosen that bind either side of each STR locus, and the primers are often labelled with a fluorescent tag.
3. The amplified fragments are separated by length using electrophoresis. Fragments with more repeats are longer.
4. The fragments are made visible and the pattern is recorded.
Why use several loci?
Two unrelated people might have the same number of repeats at one locus by chance. The chance that two people match at every one of 16 loci is extremely small, often quoted as less than one in a billion. Using more loci makes the profile more reliable.Because a profile is inherited, relatives share more bands than unrelated people. A child's profile contains bands from both parents. DNA profiles are used in forensic science, paternity testing, identifying disaster victims and in conservation to check breeding records of animals.
1. DNA is extracted from a sample such as blood, saliva, hair roots or skin cells.
2. PCR is used to amplify the STR regions. Primers are chosen that bind either side of each STR locus, and the primers are often labelled with a fluorescent tag.
3. The amplified fragments are separated by length using electrophoresis. Fragments with more repeats are longer.
4. The fragments are made visible and the pattern is recorded.
Why use several loci?Two unrelated people might have the same number of repeats at one locus by chance. The chance that two people match at every one of 16 loci is extremely small, often quoted as less than one in a billion. Using more loci makes the profile more reliable.Because a profile is inherited, relatives share more bands than unrelated people. A child's profile contains bands from both parents. DNA profiles are used in forensic science, paternity testing, identifying disaster victims and in conservation to check breeding records of animals.