A genetics study compared four mouse strains across two factors: presence of gene X (yes/no) and high-fat diet (yes/no). Average body fat (%) outcomes: Strain A, gene X yes + high-fat yes, 38%; B, gene X yes + high-fat no, 22%; C, gene X no + high-fat yes, 31%; D, gene X no + high-fat no, 18%. The researchers argued that gene X has an <em>independent</em> effect on body fat that doesn't disappear when diet is controlled. The strongest data support is ______
Which choice most logically completes the text using the data above?
- A
Strain A's 38% body fat.
- Bcheck_circle
the comparison A vs. C (both high-fat: 38% vs. 31%) and B vs. D (both no high-fat: 22% vs. 18%)—gene X adds 4-7 points in both diet conditions.
- C
Strain D's 18% body fat.
- D
the comparison A vs. D, showing both effects.
Explanation
To show gene X's independent effect, hold diet constant and vary the gene. Choice B does this in both diet conditions, showing gene X adds 4-7 points regardless of diet, supporting the independent-effect claim.