Figure 1. Bias in Mendelian randomization studies which do not account for parental genotype.

Figure 1 is reproduced from Figure 1; Morris et al., 2020. Population stratification due to ancestral differences (yellow lines), dynastic effects (red lines), and assortative mating (green line). In within-family Mendelian randomization, parental genotype is controlled for, so effect estimates for the influence of child’s genotype on child phenotypes are unbiased by these processes.