**Alpha level**
is the type 1 error rate for the genetic association study.

**Maternal genetic effect**
is the proportion of variance in the trait explained by maternal genetic effects at the locus.

**Offspring genetic effect**
is the proportion of variance in the trait explained by offspring genetic effects at the locus.

If you have an effect size estimate and allele frequency for the genetic variant of interest, you can calculate the proportion of variance in the trait explained as

(2*P*(1-P)*b^2)/VAR(trait), where P=allele frequency, b=effect size estimate.

between the phenotypes after the effect of the locus has been removed. This is likely to be close

to the phenotypic correlation between maternal and offspring phenotypes as the majority of loci will have a small effect.

NB. Maternal and offspring genetic effects can only be estimated uniquely when there are genotyped individuals who report their own phenotype and genotyped individuals who report their offspring's phenotype. These individuals do not need to be overlapping.

If you use the Maternal and Offspring Effects Power Calculator in your research please cite: Moen G, Hemani G, Warrington NM, Evans DM (accepted). Calculating power to detect maternal and offspring genetic effects in genetic association studies. Behav Genet.

R code for the Maternal and Offspring Genetic Effects Power Calculator can be found here.