Concepts in Human Genetics

When similar phenotypes or disease conditions can be caused by different genotypes, this may produce heterogeneity. 

Allelic heterogeneity occurs when different alleles of the same gene produce clinically similar conditions. 

Locus heterogeneity refers to the condition when mutations of more than one gene or locus can produce similar disease states. 

Variable expression arises when the nature and severity of the phenotype for a genetic condition varies from one person to another. 

Pleiotropy refers to a condition in which a mutant allele may have different phenotypic effects in various organ systems in an affected person. 

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