Human genome consists of 6,000,000,000 pairs of bases that present the letters of the genetic alphabet.The genome of each individual is a unique combination formed by combining the genetic material of its parents. With the exception of identical twins, there are no two individuals in the world with identical genetic material.

For purposes of identity determination Genos DNA laboratory analyses STR (Short Tandem Repeat) sequences that show significant difference from individual to individual. Standard paternity test includes the following loci: D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TPOX, D18S51, D5S818 and FGA. Additional loci can be analysed if requested.

If differences exist in only one locus, one can assume that it is a mutation. If differences exist in more than two loci, then without any doubt the analysed person is not a parent to this child. Paternity is most commonly determined by comparing the genotypes of mother, child and potential father. Probabilities of paternity usually range from one in several million to one in several billion.
Fatherhood and motherhood can also be established without the other parent. Then the probability is something smaller, but still very persuasive. The minimal probability that is considered to be necessary to establish the paternity is 1:10.000, i.e. 99.99%. Other relatives can also be used to indirectly determine paternity.

Thanks to the use of modern technology DNA analysis is performed from buccal (cheek) swabs and there is no need for drawing blood. If for some reason oral swabs are not available, many different samples can be used to test paternity (chewing gum, toothbrush, cigarettes, used tissues, etc.).

Prenatal paternity testing and sex determination:

The method is based on analysis of 23 STR loci on fetal Y chromosome (therefore prenatal paternity test is limited to male fetuses). Although this type of test is possible from 12 weeks of pregnancy, we perform it from 14th week, due to the ethical issues.

Also, it is important to emphasize that due to the paternal inheritance of the Y chromosome, prenatal paternity test cannot be performed in cases when alleged fathers are related through their male lineage. For the same reason our recommendation is to test all alleged fathers. However, testing of one alleged father is acceptable, as long as the client is aware of limitations of Y-STR testing if the alleged fathers are potentially related.

Even when the sex of baby is determined by sonogram, we always process the blood sample first and after we get the Y-STR profile, we start to process the sample of alleged father. So both samples should be sent at the same time but we do not charge the client for the buccal swab analysis until we confirm the result for the baby (since we had some cases when the sex determined by sonogram was not accurate, which was confirmed after the baby was born). Also, since the amount of cell-free fetal DNA varies (due to individual-to-individual variation, gestational age, high BMI, multiple pregnancy), there is a possibility that not all of the tested loci are amplified which may lead to inconclusive results.

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