Linked alleles do not obey Mendel's laws because they tend to go into the gametes together. Crosses involving linked genes do not give same results as unlinked genes. Heterozygote forms only two types of gametes and produces offspring with only two phenotypes. Crossing-over causes recombinant gametes and at fertilization, recombinant phenotypes. Percentage of recombinant phenotypes measures distance between genes to map the chromosomes.
Linked genes indicate the distance between genes on the chromosomes.
If crosses are performed for three alleles on a chromosome, only one map order explains map units. Changes in chromosomes or genes that pass to offspring if they occur in gametes. Mutations increase the amount of variation among offspring. Chromosomal mutations include changes in chromosome number and structure. Monosomy occurs when an individual has only one of a particular type of chromosome.