What does recombination frequency measure in genetic mapping?

• A. The proportion of offspring with parental phenotypes; indicates linkage.
• B. The proportion of offspring with new mutations; indicates mutation rate.
• C. The proportion of offspring with the same phenotype as parents; indicates inheritance.
• D. The proportion of offspring with recombinant phenotypes, reflecting crossing-over between genes; used to estimate distance between genes.

Answer: (D)