Genetic mapping is a key tool for classical genetics. When a phenotype or a disease is observed, it is always desirable to determine where the gene is located.
Linkage means when gametes form, genes are not assorted independently, instead, they are linked together. This is because these genes are located close to each other on the same chromosome. Linkage can be tested by chi square.
Genes located close enough can crossover and then recombination occurs. The recombination frequency can be used to measure the genetic distance between two markers: the longer distance, the more recombination events, the higher recombination frequency.
Genetic map is a chromosome map of a species or experimental population that shows the position of its known genes and/or markers relative to each other. It is based on the frequencies of recombination between markers. Genetic mapping can be carried out by two-point or three-point testcrosses.