A type of inheritance in which a trait or disease manifests itself only if both alleles of a gene (derived from the mother and father) are mutant (recessive). Main characteristics: Inheritance occurs through autosomes, the trait manifests itself only in a homozygous state, parents can be carriers of a mutant gene and still be healthy, the probability of inheritance depends on the status of both parents. Examples of diseases are: Tay-Sachs disease (a disease that affects the central nervous system), phenylketonuria (a disease associated with a disorder of amino acid metabolism, in which the body is unable to break down phenylalanine from protein foods), galactosemia (a disease characterized by a metabolic disorder in which the body is unable to process galactose).