11111 Fact Sheet 17 | FORENSIC, PATERNITY AND ANCESTRY DNA TESTING

This fact sheet describes the DNA testing () process for non-medical purposes of forensic, paternity and ancestry analysis.

In summary  DNA testing for forensic, paternity and ancestry looks for small differences and similarities between individuals in their DNA  DNA profiling (DNA pattern) can be used to estimate the chance that two samples are from the same person  Informed consent from both , quality control of the test and availability of counselling are important for paternity testing  Ancestry testing looks for clues about where ancestors might come from and relationships in families.

DNA TESTING Like genes, non-coding DNA contains large DNA testing is the analysis of information in our numbers of repeated chemical letters (A,G,T,C) and genes that provide the along its length. The number of times that a instructions (the code) for making proteins. DNA sequence is repeated within a length of non- testing for forensic, paternity and ancestry looks coding DNA can range from just a few to for small differences and similarities between hundreds. people in their DNA. This type of testing usually As we have evolved, changes have built up in our involves analysis of regions between genes (non- non-coding DNA as well as our genes. We all have coding DNA) and compares the findings to small variations in our genetic code. That is why databases to look for similarities. DNA testing that we are unique. looks for specific variations across the whole is now also being used. DNA – DIFFERENCES AND SIMILARITIES IN HUMANS ABOUT DNA  Most humans are overwhelmingly alike in DNA contains the instructions for growth and their sequence of letters in their DNA although development in humans and all living things. Our each person’s sequence is unique (except for DNA (DeoxyriboNucleic Acid) is packaged into identical ) chromosomes that contain all our genes that  DNA samples from two people differ on provide a code for making proteins. average at only one letter or ‘base’ per The DNA code is made up of very long chains of thousand. Therefore, 1 per 1,000 of 6 billion four basic building blocks (nucleotide bases) called bases means there are about 6 million Adenine (A), Guanine (G), Thymine (T) and differences in the total DNA of two unrelated Cytosine (C) and different combinations of these people. these variations are enough to chemical ‘letters’ makes the code. There are about produce all the genetic differences between 6 billion bases and over 20,000 genes found in the these two people DNA of each person and each gene has its own  The closer two people are related to each specific location on a or on the other, the greater the chance their DNA mitochondrial DNA. Genes plus the region sequence will be similar between each gene (non-coding DNA) make up a  The small differences and similarities in the person’s genome. Mitochondria, small units in the DNA sequence between people are used in cells involved in energy production, have their DNA testing to determine the identification of own separate DNA. individuals.

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22222 Fact Sheet 17 | FORENSIC, PATERNITY AND ANCESTRY DNA TESTING

TESTING NON-CODING DNA FOR NON- MEDICAL Step 3: PURPOSES  To select out the pieces of DNA that need to Unlike tests on DNA for medical purposes, non- be looked at, the pieces of DNA that have coding DNA testing looks at specific areas called spread through the gel are covered with loci (singular ) in the non-coding DNA that are special DNA primers. generally not related to our health.  A primer is a piece of DNA used to detect sequences. The primers are made in the These loci are found at a number of sites on each laboratory and contain a match for the DNA chromosome. The loci used for DNA testing are sequence that the test is looking for those that have different numbers of the repeated  The primers in fact have the opposite sequences in different people in the population. sequence to the sequence being tested for. All our chromosomes come in pairs, which means They match up because of the ability of the that each person has two partnering loci for every letters A and T, and C and G to pair with each paired chromosome. They will have a specific other as shown in Figure 17.2 number of repeats at each of these loci on both  If the person’s DNA on the gel contains the their chromosomes, and this number of repeats matching sequence, the primer will combine may be the same or different between the (hybridise) with the person’s DNA at the site of partnering loci. the matching sequences  Chemicals such as fluorescent dyes are Information from specific loci is used to create a attached to the primer. When the gel is DNA pattern or DNA profile for each person. exposed to a certain type of light, the DNA on the gel that has been detected as containing a CREATING A DNA PROFILE (OR PATTERN) FOR A particular sequence of ‘letters’ will show up. PERSON The remaining DNA will not be visible The basic principles underlying how DNA testing is  When a number of different primers are used done includes (Figure 17.1): to detect different repeats of sequences, the Step 1: gel will look like a series of bands as shown in  In the laboratory, using a technique called Figure 17.3. Each band represents a site or polymerase chain reaction (PCR) produces locus on the non-coding DNA at which a many copies of DNA called short tandem specific repeated sequence is located repeats (STRs) which are specific short  Some of the bands appear darker than others. sequences of the DNA letters This is because that person has the same Step 2: number of repeated sequences of letters on  The copied DNA is placed into a slab of jelly (a each of their two chromosomes where the gel matrix) and an electrical current is applied locus is located. The band is showing the same so that the jelly becomes electrically charged pattern from each chromosome and so the and has a positive (+) end at the top and a two bands are lying on top of each other on negative (-) end at the bottom, just like the the gel positive and negative ends of a battery  A person can only ever have one or two bands  As the DNA is a chemical which has a negative for each primer charge, the DNA is pulled towards the positive end of the gel or from the top to the  In Figure 17.3, Persons 1 and 2 have the same bottom banding pattern for primer 5 and persons 2  The pieces of DNA separate along the gel and 3 have the same pattern for primer 7. according to size: the biggest pieces move the  That is why it is necessary to use a number of slowest and so will remain near to the top of different primers to enable differentiation the gel between different people  The gel now contains all of the person’s DNA spread from the top to the bottom of the gel.

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33333 Fact Sheet 17 | FORENSIC, PATERNITY AND ANCESTRY DNA TESTING

Figure 17.1: Genetic testing to create a DNA profile of a person. Image from yourgenome, Genome Research Limited at https://www.yourgenome.org/facts/what-is-a-dna-fingerprint

Figure 17.2: Using a probe (primer) to detect a repeated sequence in the non-coding DNA of a person.

 The bands at the bottom of the gel represent At the bottom the sequence may be made up shorter sequences of letters than at the top. of only four letters repeated 10 times so it will For example, a band at the top of the gel may be only 40 letters or bases long. represent a sequence of five letters repeated These patterns of bands have become known as a 30 times so it will be 150 letters or bases person’s DNA profile (Figure 17.3). long.

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44444 Fact Sheet 17 | FORENSIC, PATERNITY AND ANCESTRY DNA TESTING

Figure 17.3: DNA profiles of three people created using seven different DNA primers manufactured in laboratory.

FORENSICS There are a number of concerns about the use of DNA profiling enables matching of samples with a DNA material in the courtroom and the high probability from crime scenes with those of establishment of DNA databases. suspects in many cases. These include:  Consent for the sample Increasingly DNA obtained from crime scenes is  Methods of its collection first checked to see if it matches with DNA profiles  Procedures to ensure that it is not stored in databases or databanks. These contaminated from the time it is taken to databases contain the DNA profiles obtained from when it is tested convicted criminals, from other crime scenes and  Storage of the sample suspects.  Its destruction after testing and Forensic DNA databases have been established in  The privacy and confidentiality of the profile many countries including the , the generated. , Canada, New Zealand and in PATERNITY TESTING . Increasingly DNA testing is being undertaken to determine maternity, paternity or other family LIMITATIONS AND CONCERNS WITH DNA relationships. PROFILING AND DATABASES Until recently, such testing was primarily paternity DNA profiling still only gives a chance or testing: that is, establishing whether a man had probability that two samples are from the same fathered a child. person. Paternity testing is based on: In forensic cases, the police usually have DNA  A child is a combination of the DNA of its from the and are seeking the chance mother and father that there is a match with the DNA from a  Using DNA profiles of all the people involved, suspect. They are given a ‘match probability’ or usually mother, child and two men the chance that the two samples match. The questioning their fatherhood, a probability higher the probability, the greater the chance that can be given for one of the men being the the samples of DNA belong to the same person. father

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 A man can be excluded as the father if he As different companies compare test results to does not match with the child on at least two different databases, ethnicity may not be loci consistent.  Inclusion as a father is usually with 99.9% In addition, findings about ethnicity may be probability different from an individual’s expectations as Concerns associated with Paternity Testing humans have mixed with different populations Paternity is often challenged in court proceedings throughout history and consequently individuals when child maintenance, custody, and succession may have many different variations in their DNA. to property is an issue. The results of DNA It is helpful to know what type of testing is being profiling will only be able to be considered by the undertaken for ancestry to ensure testing will Family Court if undertaken by a laboratory provide some clues to the questions being asked. accredited for paternity testing. Three types of genetic ancestry testing are Paternity tests, however, are now available commonly used: commercially, by mail order and through the internet. Y chromosome testing (YDNA testing): This is used to explore ancestry in the direct male This raises important issues for consideration line. Y chromosome testing can only be done on including: males because females do not have a Y  The importance of informed consent by both chromosome. As the Y chromosome passes down parents for a sample to be taken from a child almost unchanged from father to son variations or  Quality control of the test undertaken short tandem repeats (STRs) in the Y chromosome  The availability of counselling after the test can indicate whether families of the same result and surname are related.  Privacy of the individuals involved, particularly in relation to mail order paternity Mitochondrial DNA testing (mtDNA testing): tests. This type of testing identifies genetic variations in mitochondrial DNA and is used to provide ANCESTRY information about the direct female ancestral line. DNA testing has recently become popular for Both males and females have mitochondrial DNA people looking for clues about where their and this type of testing can therefore be used on ancestors might come from and about both sexes. However, mitochondrial DNA is only relationships in families. passed on by the mother and therefore tracks the female ancestral line only. Genetic ancestry testing looks at the level and Autosomal DNA testing (atDNA): type of genetic relationship between individuals. These tests evaluate large numbers of variations As in other DNA testing, it analyses repeats of DNA across a person’s entire genome. The results are sequences of letters or large numbers of compared with those of others who have taken variations across the whole genome and compares the tests to provide an estimate of a person’s them to databases to look for similarities. ethnic background. This type of test may be used Ancestry testing is based on the fact that: because Y chromosome and mitochondrial DNA  Certain patterns of genetic variation are often test results represent only single ancestral lines, shared among people of particular and do not capture the overall ethnic background backgrounds of an individual. However results may show some  The more closely related two individuals, variations between family members. families, or populations are, the more Larger research studies are currently being patterns of variation they typically share. conducted by scientists to explore the history of populations as they arose, migrated, and mixed Ancestry testing has a number of limitations Ancestry testing is commonly offered as an online with other groups. test through private companies.

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