Correct! Without scales, oxygen diffuses directly through icefish skin.Select another correct answer. You selected all the correct answers.

Icefish gills are white because icefish lack hemoglobin and red blood cells; colorless gills do not help them obtain oxygen. Try again.

Icefish blood is clear because icefish lack hemoglobin and red blood cells; this does not help them obtain oxygen. Try again.

Icefish hearts are colorless because icefish lack hemoglobin and red blood cells; this does not help them obtain oxygen. Try again.

Antarctic water temperatures are cold enough to freeze blood, even without hemoglobin. Try again.

Antarctic water temperatures are cold enough to freeze blood, even without red blood cells. Try again.

Correct! Icefish have many adaptations that allow them to inhabit extremely cold waters. For example, they produce antifreeze proteins, which prevent ice crystals from forming in their blood. Select another correct answer. You selected all the correct answers.

Correct! Icefish lack red blood cells, which makes their blood thinner. Other adaptations that allow their blood to flow more freely include large hearts, large-diameter blood vessels, a large blood volume, low blood pressure, and a low metabolic rate. Select another correct answer. You selected all the correct answers.

Correct! Notothenioids’ antifreeze proteins allow them to thrive in a place where other fish species cannot live. Select another correct answer. You selected all the correct answers.

Only one species of notothenioid, the icefish, lacks a functional globin gene. The other notothenioid species have hemoglobin (and functional globin genes). Try again.

Notothenioid fish generally have a functional antifreeze gene. Try again.

Only one group of notothenioids, the icefish, has colorless blood. The rest, like all other vertebrates, have red blood. Try again.

The antifreeze gene arose through several steps. Try again.

Correct! Genes can become duplicated by accident and then mutated. In this case the mutated gene provided the organism with a selective advantage in cold waters. The formation of the antifreeze gene in notothenioids is an example of "inventing something new from something old." Select another correct answer. You selected all the correct answers.

The cold waters provided a selective advantage to fish with the antifreeze gene once that gene arose, but cold waters do not cause particular mutations to occur. Try again.

The icefish antifreeze gene evolved after Antarctica broke away from South America, 34 million years ago. Before then, Antarctic waters were not as cold as they are now and the antifreeze gene would not have provided a selective advantage to fish. Try again.

Natural selection does not cause mutations. Mutations occur at random and natural selection selects for or against them. Try again.

The icefish globin gene was no longer necessary, so its loss did not harm the icefish. Try again.

Correct! Gene "death" occurs when a mutation or mutations inactivate a gene’s function. If this function is no longer critical, the resulting loss causes no harm to the organism. In a sense, the gene "dies." Select another correct answer. You selected all the correct answers.

The nonfunctional icefish globin gene shows the mutations that disabled it—the "fossilized remnants" of the gene referred to in the film. Try again.

Correct! Over time, a strong selective pressure will cause the proportion of individuals with a favored characteristic to increase because they will have more offspring than individuals without the favored characteristic. Select another correct answer. You selected all the correct answers.

Selection acts on the characteristics of individuals (which are affected by mutations), but it does not cause mutations. Try again.

Individuals don’t evolve. Evolution changes the proportion of individuals with certain characteristics in a population over time. Try again.

Selection acts on the characteristics of individuals and depends on the environment these organisms live in. Try again.

Only the "birth" of the antifreeze gene involved a gene duplication. Try again.

Only the "death" of the globin gene destroyed the function of an unnecessary gene. Try again.

Only the "birth" of the antifreeze gene is an example of inventing something new from something old. The "death" of the antifreeze gene merely destroys something old. Try again.

Correct! Mutation underlies both the birth and death of icefish genes. However, each process involved different types of mutations. Select another correct answer. You selected all the correct answers.