Question

which of the following statements about gene expression is true?
if you are born with a gene for a recessive trait, you will have that trait.
if you are born with a gene for a dominant trait, you will have that trait.
dominant genes always manifest unless a gene mutation is present.
even if you are born with a dominant gene, environmental factors may influence whether the trait is expressed.
question 12 (2.5 points)
the text describes research by caspi et al. (2002) on criminal behavior, child abuse, and the gene that causes low levels of the enzyme monoamine oxidase (mao). low levels of mao have been linked to aggressive behavior. the researchers found that among abused boys, those with the gene causing low mao levels were far more likely to have committed a violent crime by age 26 than those with the gene causing high mao levels. this study is evidence that
environmental factors impact behavior as much as biological factors do.
biological factors can impact behavior, but environment plays a much stronger role.
environmental factors impact behavior more than biological factors do.
the effect of biological factors on behavior can depend on environmental factors.

Explanation:

First Question (About Gene Expression)

• For the first option: A recessive trait is expressed only when two recessive alleles are present (homozygous recessive). Having one recessive gene (heterozygous) won't show the trait. So this is false.
• Second option: A dominant trait is expressed when at least one dominant allele is present, but there are cases (like incomplete dominance, or environmental influences) where even a dominant gene might not fully manifest the trait as expected. However, compared to recessive, dominant traits are more likely to be expressed if the gene is present. But the fourth option is more accurate about environmental influence. Wait, no—let's re - evaluate. Wait, the fourth option says "Even if you are born with a dominant gene, environmental factors may influence whether the trait is expressed." This is correct because gene expression can be influenced by the environment (epigenetics, for example). The second option: Just having a dominant gene doesn't always mean the trait is expressed. For example, in some cases of penetrance, a dominant allele might not be fully penetrant. But the fourth option is a true statement about gene expression and environment. Wait, but let's check each:
• Option 1: Recessive trait needs two recessive alleles (in simple Mendelian terms), so having one recessive gene (with a dominant allele) won't show the trait. False.
• Option 2: Dominant trait is expressed with one dominant allele, but there are exceptions (like incomplete penetrance, or environmental effects). But the fourth option is about environmental influence on dominant gene expression, which is a known phenomenon. However, the second option: Is it always true? No. But the fourth option is a true statement. Wait, but the question is which is true. Let's think again. The fourth option: "Even if you are born with a dominant gene, environmental factors may influence whether the trait is expressed." This is true. For example, the expression of genes related to height (a dominant - influenced trait) can be affected by nutrition (environmental factor). The second option: "If you are born with a gene for a dominant trait, you will have that trait." This is not always true. There are cases of incomplete penetrance where a dominant allele is present but the trait is not expressed. So the fourth option is true. Wait, but maybe I made a mistake. Wait, the third option: "Dominant genes always manifest unless a gene mutation is present." No, because environmental factors can also affect expression, not just mutation. So the correct answer for the first question is the fourth option: "Even if you are born with a dominant gene, environmental factors may influence whether the trait is expressed."

• The study is about abused boys (environmental factor: child abuse) and a gene (biological factor: MAO gene) related to aggressive behavior. Among abused boys, those with the low MAO gene were more likely to commit violent crime. This shows that the biological factor (the gene) had an effect on behavior, but this effect was seen in the context of an environmental factor (child abuse). So it's not that one is stronger than the other, but that the effect of the biological factor depends on the environmental factor (being abused).
• Option 1: The study doesn't show they impact equally, just that the biological factor's effect depends on environment. False.
• Option 2: The study doesn't say environment is stronger, just that the gene's effect was seen in the abused group. False.
• Option 3: The study doesn't show environment is more impactful, it shows the gene's effect depends on environment. False.
• Option 4: "the effect of biological factors on behavior can depend on environmental factors." This matches because the gene's effect (biological) on criminal behavior was seen more in the context of child abuse (environmental factor).

Answer:

Even if you are born with a dominant gene, environmental factors may influence whether the trait is expressed.

Second Question (Caspi et al. Study)