I’ve written an R Shiny app to illustrate the mathematical relationships among genotypic values, allele frequencies, the additive effect of alleles, and components of the genetic variance. I haven’t yet revised the accompanying notes, but when I do you’ll be able to find them at http://darwin.eeb.uconn.edu/eeb348-notes/quant-intro.pdf.
As a reminder, you can find a list of all of the R Shiny apps I’ve written on Github, where you can also download all of the source if you want to run the apps locally.