The video below is the second in the series Brainwash, a Norwegian documentary on the science of nature and nurture. This episode concerns parental influence, and features a very clear explanation by Robert Plomin of heritability as determined by adoption studies. (Note to experts: Plomin refers to his Colorado adoption study, but even larger studies have replicated the results, across multiple countries. He found that the effect of shared environment on cognitive ability was consistent with zero, but the actual value could be somewhat higher due to statistical uncertainties. See The mystery of non-shared environment for more discussion.)
Brainwash caused a big controversy in Norway, but I think the narrator does a great job of making the presentation fair, accurate and entertaining. His background is standup comedy :-)