Table 3.

Expected Frequencies of Control-Mother Pairs Under the Multiplicative Model 1^a

	C = 0	C = 1	C = 2
M = 0	(1 − b)[μ00 + (1/2)μ01]	(1 − b)[(1/2)μ01 + μ02]	0
M = 1	(1 − bS1)[(1/2)μ10 + (1/4)μ11]	(1/2) [(1 − bS1R1M)μ10 + ((1 − bS1(1 + R1M)/2)μ11 + (1 − bS1)μ12]	(1 − b R1MS1)[(1/4)μ11 + (1/2)μ12]
M = 2	0	(1 − b R1MS2)[μ20 + (1/2)μ21]	(1 − b R1MS2)[μ22 + (1/2)μ21]

^aM and C denote the number of copies of the allele carried by the mother and child, respectively. is a normalizing constant, and b is the frequency of preterm delivery in infant-mother pairs where neither carries a copy of the allele under study. The subscripted μ parameters are stratification parameters for the parental mating types, incorporating their possibly distinct baseline disease rates. S₁ and S₂ are the relative risks associated with maternal carriage of 1 or 2 copies of the allele, respectively, while R_1M is the relative risk associated with fetal inheritance of a maternal copy of the allele.