Sometimes it may be necessary to evaluate the likelihood that a person is the product of an incestuous mating based only on analysis of the person. This may occur when a child is placed for adoption or when the parents are unknown or not available. Examination of several alleles can either support or exclude the hypothesis of incest.



Likelihood Ratio of incest-to-nonincest


(f + ((1 – f) * q)) : q


(1-f) : 1



• f = inbreeding coefficient (see previous section)

• q = allelelic frequency



(1) Analyze a number of genes that are inherited independently.

(2) Identify if the person is homozygous or heterozgyous for each gene.

(3) Calculate the likelihood ratio for each according to the table above.

(4) Convert the likelihood ratios to lod scores (logarithm base 10).

(5) Add the lod scores.

(6) Convert the total lod score back to a likelihood ratio to get the likelihood ratio of incest to nonincest


total likelihood ratio for incest to nonincest =

= 10 ^ (total lod score)


If several homozygous foci are present for low frequency alleles, then the probability of an incestuous mating for the parents will be high.


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