Genes present near to each other have less probability of being separated onto different chromatids during chromosomal crossover. Therefore, when a cluster of genes show linkage behaviour, they do not show independent assortment.
Related Theory
The strength of linkage between two genes is inversely proportional to the distance between them in the chromosome i.e., it decreases with increase in distance between the genes. It ensures the maintenance of parental trait in the offspring and reduces the chance of creation of variability with sexual reproduction.