The size and shape of the vertebrate skull can reveal a great deal about an animal's lifestyle and evolutionary relationships. Consider your own skull. If you put your finger in your ear and move your jaw up and down, you can feel the space near the hinge of your jaw. Nestled in this space are the tiny bones that make your hearing possible: the malleus, incus, and stapes. All mammals have these three ear bones, but reptiles such as this T. rex don't. Where did ear bones come from? Gene expression patterns can be used to test hypotheses based on morphology. For example, the regulatory gene Bapx1 is expressed in the hinge of the developing lower jaw in fishes and reptiles. Where would you predict Bapx1 expression to occur in mammals?

Video transcript

Hi everyone. Here's our next question. It says gene expression can cause different cells to have different proteins that are vital for their respective functions. It can be regulated during the transcription or translation process. Which of the following does not affect gene expression. Choice A says exposure to harmful substances. Ah Well this does express affect gene expression. Many harmful substances are harmful because there are mutations they actually mutate a person's DNA. So this could definitely affect gene expression. So that's not our answer choice B. Is age age definitely affects gene expression. Um With age the telomeres decrease in length. Those are the structures at the end of chromosomes and their protective, preventing the D. N. A. From degrading. And each time cells divide the telomeres shorten each time. And so with age the D. N. A. Is less protected by the telomeres. Um Also oxidative stress as individuals age often through inflammation can cause damage to D. N. A. In the body and affect gene expression. So age definitely has an effect and therefore is not our answer. Choice C. Is temperature in the environment um definitely can affect gene expression. A dramatic effect would be um sex determination in some eggs, turtle eggs, crocodile eggs. Um Certain genes involved in sex determination in those animals are temperature sensitive and are expressed at greater levels at different temperatures. So depending on the temperature at which the eggs are incubated you'll see more males or more females. So that temperature can definitely have an effect on gene expression. So finally we left a choice the interaction with other people. Um You would not expect that to affect gene expression so we can select choice D interaction with other people as something that would not affect gene expression. See you in the next video.