THE EFFECT OF RELATIVES ON THE LIKELIHOOD RATIO ASSOCIATED WITH DNA PROFILE EVIDENCE IN CRIMINAL-CASES

In DNA profiling sometimes a match is declared between the DNA profile from a suspect and that from a scene-of-crime DNA sample. DNA evidenc e has frequently been presented in the form of a likelihood ratio, the ratio of the probabilities of the data set under the two hypotheses o f a single and two sources for the matching DNA profiles. The calculat ion of the probability of a match is usually performed using a product rule with information from an appropriate database. This approach has been criticized for failing to allow for genetic relatedness, such th at the suspect could be a close relative of the source of the scene-of -crime DNA profile. This paper suggests ways of incorporating the poss ibility of relatives into the likelihood ratio, and shows that unless there is strong evidence implicating a full sibling of the accused, al lowing for possible relatedness has very little impact.