4. Single gene disorder - Hereditary disorder caused by a mutant allele of a single gene. Chromosome Abnormalities- A chromosome abnormality or aberration reflects an atypical number of chromosomes or a structural abnormality in one or more chromosomes. Multifactorial Disorders- These are caused by mutations in multiple genes, which may interact with environmental factors Counseling helps the parents having a diseased child Karyotyopes can help predict the chances of two parents having a diseased child because you can use the parents chromosomes and combined them to see the possibilities of them having a kid with a disease.