So now that we've introduced polygenic inheritance in our last lesson video, in this video we're going to introduce pleiotropy. Pleiotropy is practically the opposite of polygenic, and that's because polygenic means multiple genes affecting one trait. However, pleiotropy is when a single gene has effects on multiple different phenotypic traits. If we take a look at our image down below here on the left-hand side, we're showing you a representation of pleiotropy. Pleiotropy is when just one single gene has impacts or effects on multiple different traits, such as traits A, B, C, and D. Pleiotropy is one gene affecting many traits. A classic example of pleiotropy is Marfan syndrome, where a mutation of just one single gene, the FBN1 gene, will limit the body's ability to build connective tissue and lead to a wide variety of phenotypic traits being affected. Some Marfan syndrome phenotypes include having a tall and slender body, long arms, legs, and fingers, a curved spine, crooked or crowded teeth, heart disease and heart murmurs, and eye conditions or vision loss. We have one single gene, this FBN1 gene, which if a mutation occurs there are effects or impacts in the body, the arms, the legs, the fingers, the spine, the teeth, the heart, and the eyes which might seem unrelated but are all traced back to this one particular gene. All of these different traits that you see here are all impacted by just one gene.

This concludes our introduction to pleiotropy and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.