distance between two linked genes upon the chromosome is measured in the units as

1. ratio of crossing over between them
2. cross-over value
3. no. of other genes between them
4. interfance value

Distance between two linked genes upon the a single chromosome is measured in the units as the cross-over value.The COV can be calculated by the percentage of offspring that show recombinationand is used to map the genes on a chromosome. A small COV for a given pair of genes indicates that the genes are situated close together on the chromosome.