Which recombination frequency indicates that two genes are perfectly linked?

1. Recombination frequency counts the fraction of progeny carrying new allele combinations. 2. Perfect linkage means no crossover ever separates the two genes, so no recombinants appear. 3. That corresponds to a recombination frequency of 0. 4. Perfectly unlinked genes give a recombination frequency of 0.5, the other end of the range. 5. Perfect linkage is exactly the case that violates Mendel's law of independent assortment. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 13 "Modern Understandings of Inheritance", section 13.1 Chromosomal Theory and Genetic Linkage_