Homology can be defined as the presence of common structures because of shared ancestry. Homology can involve genes, proteins, or anatomical structures. As a result of 'descent with modification,' many homologous structures have adapted different purposes. Under what circumstances might one expect proteins of similar function to not share homology? Would you expect such proteins to be homologous at the level of DNA sequences?

Video transcript

Welcome back. Let's look at our next problem. The pax six gene carries genetic the genetic information that encodes the pax six protein which controls i development and other sensory organs. The pax six from other vertebrates and Drosophila. Eyeless gene share similar sequences and functions. This can indicate. And we see that we've got choice, a analogy choice be ornithology, choice C. Pathology or choice D. Zen ology. Well, we know we have here genes from very divergent species and yet they still share similar sequences and functions and that's despite their divergence from each other. So we look at our answer choices. Choice B. Ornithology. Orthe ologists. Ornithologist genes are homologous genes that are still similar despite a speciation event. So those similarities are due to descent from a single gene in the last common ancestor. So despite these 22 species growing apart becoming very different they still have this shared gene from a common ancestor. So let's look at our other answer choices to understand why they're not correct. Choice a analogy. Well, analogous structures are where you have similarity in function not do to a common ancestor. So instead of that similarity and function and sometimes inform being due to descent from a common ancestor in analogy you have that similarity due to similar environments. Similar evolutionary pressures to create that structure. So that's why that's not correct. Oh I see. Para ology is when genes you have homologous genes due to um gene duplication. So it's in a single organism. You had a gene duplication event. And now you have two homologous genes within that same organism. So not the example of genes that were still similar despite a speciation event, That's why that's not correct. And then finally Choice D. Is enology. And in that case you have homologous genes again. But that's due to horizontal gene transfer from another species. So not due to descent from a common ancestor but due to a gene being transferred from an over from another species. So that's why that's not correct. So again with we had the pax six gene um necessary for eye development and the pax six gene invertebrates and the shuffles eyeless gene share similar sequences and functions. This can indicate choice B or theology. See you in the next video.