The strength of the genetic linkage measures the probability with which recombination will occur between two genes on a chromosome. This is determined by the distance between the location of the particular genes on the chromosome and also the frequency of recombination at the given site on the chromosome. The existence of a genetic linkage is the reason why the behaviour of many pairs of genes is not governed by Mendel’s second law, i.e. the law of independent combinability of predispositions. The strength of a genetic linkage can be measured from the ratio of the number of descendants in which recombination occurred between the particular genes and the number of descendants without recombination in this section. If there is the same number of both types of individuals in the progeny (for example, if the genes are located on different chromosomes), the genetic bond is zero; however, if the genes are close together on the same chromosome or if recombination does not occur in the area between the genes for some reason, the bond between the genes can be practically absolute.