What causes variation in quantitative traits?

What is environmental variance? What is genotypic variance? What is phenotypic variance, and how is it related to the environmental variance and genotypic variance in a population? How can we use an inbred strain to directly measure environmental variance? This video lecture was recorded at the University of Wisconsin -- Stout in the fall of 2021. It accompanies my BIO 332 Genetics course, which was taught with Hartl's "Genetics: Analysis of Genes and Genomes."