Mendelian disorders refers to those disorders usually caused by mutation in a single gene, and follow the basic Mendelian principles of inheritance. Since, genes are affected, mendelian disorders belong to the category of genetic diorders. Chromosomal disorders, on the other hand, are those disorders caused due to changes in chromosome number or structure. SInce, genes are located on chromosomes, chromosomal disorders lead to changes in gene structure, arrangement, etc., and hence chromosomal disorders too are a type of genetic disorder.