One of the first Mendelian traits identified in humans was a dominant condition known as brachydactyly. This gene causes an abnormal shortening of the fingers or toes (or both). At the time, some researchers thought that the dominant trait would spread until 75 percent of the population would be affected (because the phenotypic ratio of dominant to recessive is 3 : 1). Show that the reasoning was incorrect.

Video transcript

Welcome back. Let's look at our next question. It says which of the following is the first Mandel Ian trait identified in humans. Well, to answer this, let's first recall, what is, what makes them and alien trait. So a million trait is one that is controlled by a single gene and follows Mendel's laws of inheritance similar to the P plants he used in his genetic experiments. So with that in mind, let's look at our answer choices here. We've got choice A which is male ness, but my illness is controlled by the presence or absence of the Y chromosome. So this is the controlled by the presence or absence of an entire chromosome, not just a single gene. So that's not an answer. Choice. Choice B is height, height is caused by many genes. The additive effect of many different genes, it is also affected by environmental factors. So nutrition for instance, can affect adult height. So not Amanda Lian trait. A modern answer. Do I see abnormal shortening of the lakes? Um This can be caused by a variety of genetic or environmental factors. So, again, not caused by a single gene. So we're looking at choice D, which is Brock. Exactly. This is indeed a mandolin trait. Um It's the, uh having this particular gene causes fingers and toes to be shorter than normal. It's a dominant gene mutation. It is caused by a single gene. And it's early discovery was a result of its something easily observable. So it could be observed that it followed this dominant inheritance pattern similar to amend and was indeed a dandelion trait. So again, which of the following is the first dandelion trait identified in humans choice D could actually see you in the next video.