ZERO-IN

Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ANALYZE IT

Instruct students to complete the Analysis Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.

When students have finished their Investigation, average the class data from Table C to determine the frequency of alleles before the population is affected by the temperature change. Enter the class average for the frequency of each allele on the board.

Average the class data from Table E to determine the frequency of alleles after the population is affected by the temperature change. Enter the class average for the frequency of each allele on the board.

Average the class data from Table H to determine the frequency of alleles of the offspring of the surviving penguins. Enter the class average for the frequency of each allele on the board.

Discuss the change in the number of penguins with each phenotype during the experiment. Students should refer to the average class data for Tables C, E, and H.

• Why was there a change in the number of penguins with each phenotype? There was a change in the ratio of phenotypes because the penguins with less dense bones starved to death. They starved because their food supply is low due to the change in the environmental conditions.

Discuss the change in the frequency of alleles during the experiment. Students should refer to the average class data for Tables C, E, and H.

Note: Tables C, E, and H from the teacher guide are also included for reference.

• How did the frequency of alleles change compared to the original penguin population? Refer to Tables C, E, and H to help you answer the question. Student answers may vary due to the random variable of reproduction. However, the frequency of the recessive allele will increase and the frequency of the dominant allele will have decreased.

• What is responsible for the change in the frequency of the alleles? The change in the climate and decrease in cold temperatures resulted in a change in the location of the food supply of the penguins. There were fewer sources of food on land and in the upper levels of the water available. As a result it was more difficult for penguins with less dense bones to obtain food than very dense bones. Therefore all of the penguins with the recessive trait survived, whereas some of the penguins with the dominant trait died. As a result, when the penguins mated, there was a change in the number of recessive versus dominant alleles that could be passed to the offspring. There was an increase in the number of recessive alleles that could be passed onto the offspring and a decrease in the number of dominant alleles that could be passed onto the offspring as compared to the before the change in the environment.

• If the weather continues to get even colder, what changes would you expect to see in the variation of phenotypes of bone density in the population? If the weather continues to get colder, the penguins with less dense bones will continue to struggle to survive and many more will probably die. The penguins with more dense bones will survive and pass on their genes to their offspring. In doing so, the trait for more dense bones will become much more frequent in the population.

• How does the process of natural selection explain the changes you saw in the different phenotypes of the penguin population and in allelic frequency? Natural selection is the process in which organisms that are adapted to their environments tend to survive and pass on their genes to their offspring. Organisms that are not as well adapted to their environment tend not to survive and do not pass on their genes. This is occurring with the trait for bone density in the penguins. The penguins with more dense bones are surviving and passing on their genes to the next generation. In contrast, the penguins with less dense bones are dying and are consequently, unable to pass along their genetic material to the next generation.

GET FOCUSED

Instruct students to complete the Focus Question in their SDRs then discuss it as a class. Use the suggested response below to guide students’ answers.

• How does genetic variation affect the type of traits or the adaptations in the individuals of a species? Genetic variation is responsible for all the different traits that an individual possesses. In our example, there was genetic variation in the trait of bone density. Before the weather turned much colder, all the penguins were living happily. However, when the environment changed, some individuals were more adapted to the environment than others. Thus, they were more likely to survive and pass on their genes.

• What is the relationship between genetic variation and natural selection? If members of a species did not have different traits no natural selection could exist because all the members of that species would be equally adapted to each environmental pressure. However, there is genetic variation in populations and some individuals are more adapted to their surrounds than others. The ones that survive are more likely to pass on their genes.

• How can an environmental change affect a population? Environmental pressures can affect the population because some members are more adapted to the new environment than others. In the experiment, penguins with more dense bones survived at a higher rate because they were more equipped to deal with the shortage of food. The environmental pressure can be natural causes (such as temperature and sunlight) or human causes (such as pesticide exposure or antibiotic exposure).

OPTIONAL EXTENSION

Instruct students to complete the Optional Extension Questions in their SDRs then discuss them as a class. Use the suggested responses below to guide students’ answers.

• How many penguins of each different phenotype survived? Student answers will vary. 8 penguins with more dense bones and 4 penguins with less dense bones survived.

• Why was there a change in the number of penguins with each phenotype? There is now an increase in the penguins with the phenotype of more dense bones because they are more adapted to this new environment. They are more likely to mass on their genes. This is called natural selection.

• Which allele is more common now? The allele for more dense bones.

• Why did many penguins not survive? They starved to death because there was not enough fish. The food supply has been greatly diminished on the land and the surface of the water. However, there is still food at the bottom of the ocean. The penguins that can dive down deeper have a better chance of survival.

• How did the frequency of alleles change as compared to the original penguin population? The frequency of alleles has changed dramatically. The dominant allele originally had a frequency of 30% and it is now down to 19%.

• What is responsible for the change in the frequency of the alleles? The change in the climate and decrease in cold temperatures resulted in a change in the location of the food supply. Fewer sources of food were available on land and in the upper levels of the water. As a result it was more difficult for penguins with less dense bones to obtain food than very dense bones. Therefore all of the penguins with the recessive trait survived. Some of the penguins with the dominant trait died. As a result, when the penguins mated, there was a change in the number of recessive versus dominant alleles that could be passed to the offspring. There was an increase in the number of recessive alleles that could be passed onto the offspring and a decrease in the number of dominant alleles that could be passed onto the offspring as compared to before the change in the environment.

• If the weather continues to get even colder, what changes would you expect to see in the variation of phenotypes of bone density in the population? Student answers may vary. If the weather continues to get even colder, further increases in the proportion of penguins with dense bones would be expected.