1090 words - 5 pages

Pretend you are adopted for a moment. You have been searching for your biological parents and you think you’ve found them. How can you know without a doubt that they are your birth parents? With the advances in DNA technology, scientists use gene frequencies and statistical analyses to ascertain the biological relationships of individuals. Harmening (2005) states, the most common use for parentage testing is the determination of whether a man is the biological father of a child. However, the testing can be used for non-classical situations such as siblingship and maternity testing.

In parentage testing, genetic markers from a child are identified and compared to the alleged parent or parents. According to Ostrowski (2003) every person has a series of genetic systems, or loci. Within each genetic system there is a pair of alleles. Half of the alleles come from the mother and half from the father. Once these alleles are extracted, amplified, and identified, they are used in a set of equations to identify three parentage indices. These indices are the paternity index, probability of paternity, and the probability of exclusion. Harmening (2005) suggests that the calculations are only valid if the tested man is compared to a “random man” that is not biologically related to him. Also, the equations must be based off of accurate gene frequencies for each genetic system and the population must be of similar ethnic background.

The first equation is the paternity index (PI), also known as the system index (SI). It is a ratio of the likelihood that an allele is passed down from the supposed father compared to an allele being passed down from a random man. Harmening (2005) states, in the equation for paternity index (X/Y), X is the chance that the alleged father can pass down the gene in question and Y is the chance that a random man can supply the same gene. If the alleged father is homozygous for the gene in question then he has a 100% chance of passing it on to the child. Therefore, X would equal 1. If the man is heterozygous for the gene then he has a 50% chance of contributing that gene making X equal 0.5. Y is the frequency of the gene which can be estimated from data gathered from a large sample population. The overall paternity index is the product off all the genetic systems calculated. The final number is the how much more likely the alleged father is capable of passing down the gene than a random man. The overall paternity index is used in the probability of paternity equation.

The translation of the paternity index to the probability of paternity (PP) requires the use of the prior probability. According to Harmening (2005) the prior of probability is based on nongenetic evidence, or social evidence. Since no lab can calculate social evidence, the unbiased number 0.5 is given. After the inclusion of this number the equation for the probability of paternity is PP=PI/(PI+1). The resulting number is expressed as a percentage. This percentage is...

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