We developed educational software to show graduate students how to plan molecular marker experiments. These computer simulations give the students feedback on the precision of their experiments. The objective of the software was to show students using a hands-on approach how: (1) environmental variation influences the range of the estimates of the magnitude of a quantitative trait loci (QTL) and; (2) how the number of F[subscript 2] plants used to map the QTL influences the range of estimates of the magnitude of the QTL. The histograms generated by the software show the range in the magnitude of the QTL genetic effect as the magnitude of the residual variance and number of F[subscript 2] plants are varied. Students will learn the influence of environmental variation on the magnitude of the QTL and why it is important to report confidence intervals for the QTL magnitude. The number of F[subscript 2] plants used in the experiment can also be varied to simulate the influence of segregating background genes that are not linked to the QTL. This software will enhance student understanding of the results of molecular marker experiments that they have either read about or conducted from their own research effort. (Contains 4 figures.)