Risch [29]: test 
against 
by the likelihood ratio test.
Holmans [12]: test 
against 
by a likelihood ratio test where the maximization with respect to the IBD probabilities is constrained to the possible triangle. By taking into account the constraints satisfied by the IBD probabilities, this test is more powerful than the unconstrained test. The asymptotic distribution of the resulting likelihood ratio statistic is a mixture of 
distributions with 1 and 2 d.f.