How could a cross between marine and freshwater sticklebacks reveal epistasis for armor traits?

How could a cross between marine and freshwater sticklebacks reveal epistasis for armor traits?

• A. The F2 generation may show non-Mendelian trait combinations and novel phenotypes if gene interactions influence plate development.
• B. Crosses always produce identical phenotypes to the parent populations.
• C. The trait distributions follow strict Mendelian ratios with no new phenotypes.
• D. Hybrid vigor is the only possible outcome.

Answer: (C)

Epistasis is at work when genes don’t act independently—one gene’s effect depends on other genes, so how armor develops isn’t just a simple tally of separate effects. In sticklebacks, armor plate formation involves multiple loci that interact, with marine and freshwater populations carrying different allele combos. Crossing these forms mixes alleles and can reveal how their interactions shape plate number and pattern, producing trait combinations that don’t follow classic Mendelian ratios and even novel phenotypes in the offspring. That’s exactly what this kind of cross can show: non-Mendelian inheritance patterns and new plate phenotypes arising from gene interactions. If traits always followed strict Mendelian ratios with no new phenotypes, you wouldn’t be seeing those interactions at work. Hybrid vigor isn’t a required outcome here either; epistasis can produce a range of results, including intermediate or unexpected phenotypes, not just increased fitness.

Epistasis is at work when genes don’t act independently—one gene’s effect depends on other genes, so how armor develops isn’t just a simple tally of separate effects. In sticklebacks, armor plate formation involves multiple loci that interact, with marine and freshwater populations carrying different allele combos. Crossing these forms mixes alleles and can reveal how their interactions shape plate number and pattern, producing trait combinations that don’t follow classic Mendelian ratios and even novel phenotypes in the offspring. That’s exactly what this kind of cross can show: non-Mendelian inheritance patterns and new plate phenotypes arising from gene interactions.

If traits always followed strict Mendelian ratios with no new phenotypes, you wouldn’t be seeing those interactions at work. Hybrid vigor isn’t a required outcome here either; epistasis can produce a range of results, including intermediate or unexpected phenotypes, not just increased fitness.