Checking relations

SampleCheck can check family relations and calculate the probability of paternity. The likelihood ratio and probability of paternity is calculated for three cases:

• when the alleged father is not related to the father,
• when the alleged father, the father and the mother belong to the same subpopulation,
• when the alleged father is a relative of the father.

Formulas

In order to see the formulas used to calculate the LR values double-click on the allele pattern and a formula dialog pops up. The formulas depend on the composition of the allele pattern. The letter p represents the frequency of the allele which the child has inherited from the mother, q represents the frequency of the allele which the child has inherited from the father, r and s are frequencies of alleles which only occur in the parents' profiles. If the child is homozygous it has qq. For most allele patterns only q is necessary to calculate the likelihood ratio, just in some cases p is also needed.

Mutations

If the tested man is eligible to be the father at all except one or two markers, we consider the possibility that he may be the father but that a mutation or two have occurred. If 12 or more STR systems are used for paternity testing, occasionally two inconsistencies can be expected even when the man is the father. But only two inconsistencies can also appear when the man is not the father. Therefore calculating a likelihood ratio for mutation is vital. A mutation likelihood ratio is a small value between 0 and 1. The formula depends on the marker's mutation rate, the frequency of the mutated allele and the distance between the original allele and the mutated one. If the mutation formula is used to calculate the likelihood ratio, you will see the word mutation instead of the allele pattern.