An extensive study was conducted on identical twins who were separated at birth. Among other things, the study showed that the individual from each pair who received better nutrition during childhood tended to score higher on standardized intelligence tests. This can best be described as an example of how

Question

A.  mutation alters phenotype.
B.  environment alters phenotype.
C.  environment alters genotype.
D.  mutation alters genotype.
E.  pleiotropic genes affect more than one trait.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain?

Gather Content
· What do you already know about genotype and phenotype? How does it relate to the question?

Consider Possibilities
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  environment alters phenotype.

Clarify Question
· What is the key concept addressed by the question?
        o This question focuses on the difference between genotype and phenotype.
· What type of thinking is required?
        o You must Apply your understanding of genotype and phenotype to this situation where identical twins experience different nutrition.
· What key words does the question contain?
        o It is important to distinguish genotype and phenotype, and mutation and environment. Genotype is the set of genes in an individual. The genotype does not change, unless it experiences a mutation. Phenotype is the description of the individual’s traits – even behavioral traits, like intelligence. The phenotype is determined not just by genes, but also by environmental influences – anything from outside the body.
        o An answer choice mentions pleiotropic genes – these are genes that act on different traits. For instance, a gene for collagen may affect the function of skin, tendons, and bones. Or a mutation in a gene that controls transcription may have dramatically different results in different cell types, depending on what genes it controls.

Gather Content
· What do you already know about genotype and phenotype? How does it relate to the question?
        o We know that identical twins share the same genes – the same genotype. Genotype doesn’t change during the lifetime of the individual.
        o Intelligence is a trait – an aspect of the phenotype. We can imagine that better nutrition allowed a healthier brain to grow in the lucky twin.
        o Nutrition is a type of environmental influence.

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o You might consider that the twin with poor nutrition may have experienced a mutation. That is possible – good nutrition can help prevent mutation-based diseases like cancer. Nutrients like antioxidant help cells to neutralize mutation-causing chemicals.
        o However, a mutation is not the likely basis for the lower intelligence score in the unlucky twin, because mutations happen in individual cells. When they cause cancer, the mutated cell may grow and produce a tumor, yet the rest of the brain is unaffected.
        o The most likely explanation is that better nutrition improved the health of the entire brain.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Since intelligence is part of the phenotype, and nutrition is part of the environment, we can conclude that this example shows how environment can alter the phenotype.
        o Does this mean that genotype does not affect intelligence?
        o Can you think of other examples in which genotype and environment work together to affect phenotype?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question required you to Apply your knowledge and understanding to this unfamiliar situation.
        o When a question like this trips you up, consider whether the scientific terms were too unfamiliar. Jotting down key terms as you read the chapter, or making flash cards may help you remember them.
        o As you learn about genetics, remember that nature is more complicated than Mendel’s early experiments would indicate. Genes are not the only influence on an individual’s phenotype – the environment is important too. Consider the effects of nutrition, infection, and even social interactions. Sometimes people call this the “nature/nurture” dichotomy. In real life, most traits are a combination of nature and nurture. In other words, an individual’s phenotype is influenced by both its genotype and its environment.