What do you think these scientists concluded about the function of the Pitx1 protein after carrying out this experiment?

1. Evaluate the following two statements as true or false. Justify your answer in one or two sentences.

A.“Having pelvic spines is always advantageous to a stickleback.”

FALSE. Pelvic spines provide an advantage in some environments but not others. One factor that appears

to favor stickleback fish with pelvic spines is the presence of large-mouthed predatory fish, such as trout.

Pelvic spines provide stickleback fish with a defense against such predators; however, pelvic spines

appear to be a disadvantage in habitats without large-mouthed predatory fish and/or habitats with

insects that can grab the spines, so that they can eat the fish.

B. “All mutations are bad.”

FALSE. A mutation is advantageous (favored), disadvantageous (not favored), or neutral (neither favored

or not favored) depends first on whether the mutation affects a trait in the organism and next on

whether that particular trait is selected for or against. The nature of the selective pressure depends on

the environment the organism lives in. Some mutations that alter a trait, such as the loss of pelvic spines

in freshwater stickleback fish, are advantageous in some freshwater environments but not all.

2) (Key Concept B) What specific features of the environment in Bear Paw Lake, Alaska, may have favored

the survival and reproduction of stickleback fish with reduced pelvises? Answer in two or three

sentences.

The lack of large-mouthed predatory fish in Bear Paw Lake meant that stickleback fish both with and

without pelvic spines could survive. Insects that live in Bear Paw Lake can grab stickleback spines to catch

the fish and eat them, which may have favored the survival of stickleback fish with reduced or no pelvic

spines. Although this is not mentioned in the film, students may note that more vegetation in freshwater

lakes could also favor fish with less armor, as they could more easily dart into hiding places.

3) (Key Concept G) In the film, Dr. Bell notes that in multiple freshwater populations and at multiple

times in history, the frequency of stickleback fish with pelvic spines decreased and the frequency of

stickleback fish with reduced pelvises increased. This demonstrates that: a) only fish with smaller

pelvises migrate to freshwater. b) similar environments select for similar genetic changes. c) the pelvis of

the marine fish is destroyed by freshwater.

4) (Key Concepts A, B, and F) Circle whether each statement below is true or false.

True/False Evolutionary change always takes millions of years.

True/False Stickleback fish lose their pelvic spines whenever they are in fresh water.

True/FalseDramatic changes in traits, such as the loss of limbs, can occur through mutations affecting a

single gene.

What did researchers discover about the genetic mutation causing the loss of pelvic spines?

What is mutated in Pitx1 in freshwater sticklebacks?

What happened to the Pitx1 pelvic switch in freshwater fish?

What do you think might be an explanation for why Morvoro lake contains fish with and without pelvic spines?