In my previous blog I indicated that I would be helping to put ‘some of the edge pieces’ onto that puzzle of biology. In the first video in this series, I demonstrated a Mendelian Monohybrid Cross and how to do Punnett Squares. In this follow-up video, let’s look at what in Mendelian Genetics is called a ‘Test Cross’. Long before DNA sequencing, this method was used to distinguish between an organism that is homozygous for a dominant trait and one that is heterozygous. It is now part of the curriculum for high school and introductory biology classes.