R and Tn genes are 10 map units apart. Mapping data from many pairs of genes can be used to determine how genes are arranged on a chromosome. The properties of genes contribute to constancy and variety of phenotypes in a population of sexually reproducing organisms. Dominance means heterozygotes and some homozygotes look alike.
Linkage holds alleles of different genes together.
Codominance allows intermediate traits. A trait may be influenced by several genes . The division of DNA into several chromosomes allows recombination . Crossover allows recombination.