rezessiver

Rezessiver is a genetic term used to describe an allele or trait that is phenotypically expressed only when two copies are present in the genotype (homozygous recessive). In a heterozygous individual, a dominant allele masks the recessive one, so the recessive phenotype does not appear. The term is common in German-language genetics and parallels the English “recessive”; “rezessiver” is the adjective form used to describe such alleles or patterns, for example “rezessiver Erbgang” (recessive inheritance).

In autosomal recessive inheritance, individuals must inherit two copies of the recessive allele to show the trait. Heterozygous individuals are typically carriers without symptoms but can pass the allele to offspring. When two carriers mate, each child has a 25% chance of being affected, a 50% chance of being a carrier, and a 25% chance of inheriting two normal alleles. In X-linked recessive inheritance, males are often affected while females are usually carriers; affected males cannot pass the condition to their sons but can pass the allele to all daughters, who become carriers.

Many human diseases are recessive, such as cystic fibrosis, phenylketonuria, or Tay-Sachs disease, though expression varies by gene and environment. Recessive traits are also important in plant and animal breeding, where breeders may select for homozygous recessive lines to fix desired characteristics.

Genetic counseling and carrier testing help assess risks for recessive conditions, especially when there is family history or in populations with higher carrier frequencies.