Genetic Profiling to Show Similarity
Use of DNA Profiling in Paternity Investigations
- In some situations, there may be questions over the paternity (and less commonly, the maternity) of a child
- A child may wish to know definitively who his/her father is and may want to be aware of possible inherited illnesses that might affect him/her in the future
- DNA profiles of the mother and child are compared, along with the profile of the alleged father (all three are needed)
- Patterns of bands are compared on all three genetic profiles
- Any band that appears in the child's profile must show in either the mother's or father's profiles; if not, the alleged true father is a different man
Worked example
Who’s the Father? – Use the DNA profiles of all 6 people shown to work out who the child’s father is:
Genetic profiling to solve paternity diagram
The child's profile can be compared to the profile of the mother and the four potential fathers to determine the identity of the actual father
Remember, any band showing in the child's profile must be present in the mother's OR father's profile, OR both. If not, that man is not the child's father.
Step 1: Look at the child's first DNA band (labelled 1)
The mother possesses this same band, so the child could have inherited that DNA from its mother. It is therefore needless to look at whether any of the men possess that band
Step 2: Look at the child's second DNA band (labelled 2)
The mother does not possess this band, so the child must have inherited it from its father. Only men B and D possess this band, so men A and C are eliminated
Step 3: Look at the child's third DNA band (labelled 3)
As with band 1, the mother possesses this same band, so the child could have inherited that DNA from its mother. It is therefore needless to look at whether any of the men possess that band
Step 4: Look at the child's fourth DNA band (labelled 4)
The mother does not possess this band, so the child must have inherited it from its father. Only men A, B and C possess this band, but A and C have already been eliminated
Step 5: Conclude that B is the father
Step 6: Look for supporting evidence from band 6
The mother does not possess this band, and the only man who possesses it is B. This reinforces the conclusion that Man B is the child's father
Use of DNA Profiling in Forensic Investigations
- DNA profiling has been used by forensic scientists to identify suspects of crimes
- Samples of body cells or fluids (e.g. blood, saliva, hair, semen) are taken from the crime scene or victim's body (e.g. rape victims)
- DNA is removed and profiled
- The profile is compared to samples from the suspect (or criminal DNA database), victim and people with no connection to the crime (control samples)
- Care must be taken to avoid contamination of the samples
- DNA profiling can also be used in forensics to identify bodies or body parts that are unidentifiable (e.g. too badly decomposed or parts remaining after a severe fire)
- DNA profiling from a crime scene can also eliminate innocent people whose DNA may happen to appear there
Genetic profiling to solve crime diagram
Using DNA profiling in criminal investigations. Suspect 3 has the most fragments in common with the crime scene DNA so it is likely that Suspect 3 is the culprit.
Use of DNA Profiling for Classification of Species
- DNA profiling of different species shows that the more similar the genetic profiles of two species, the more closely related those two species are (and the more recent in time their common ancestor is)
- This means that the DNA profile of one mammal is more closely related to all other mammals than to any other vertebrate groups
- Collecting data on species in this way allows scientists to classify organisms and develop an understanding about the evolutionary relationships between them
