What is transgressive segregation and how might it appear in stickleback hybrids?

• A. Offspring exhibit trait values beyond the range of both parents due to recombination of parental alleles.
• B. Offspring are always intermediate between parents.
• C. Offspring exactly match one of the parental phenotypes.
• D. Transgressive segregation refers to increased mutation rates.

Answer: (D)

Transgressive segregation is when hybrid offspring show trait values that exceed the range seen in either parent, due to new combinations of parental alleles coming together through recombination. In sticklebacks, marine and freshwater populations carry different alleles at multiple genes that influence traits like armor plating, spine length, or body size. When these populations hybridize, the mix of alleles can add up in ways that push a trait beyond both parents’ extremes, producing hybrids with either more or less armor, longer or shorter spines, etc., than either parent showed. This isn’t about mutation or simply being intermediate between parents; it’s about novel, extreme phenotypes arising from the combination of parental genetic variation.