rezessiven

Recessive, or rezessiven in some languages, refers to a mode of genetic inheritance where an allele is expressed in the phenotype only when two copies are present. In a diploid organism, each gene has two alleles, one on each homologous chromosome. If one allele is dominant and the other recessive, the dominant allele largely determines the trait in heterozygotes. Only individuals with two recessive alleles (homozygous recessive) show the recessive trait.

Carriers, or heterozygotes, have one dominant and one recessive allele and typically do not display the recessive phenotype, but they can pass the recessive allele to offspring. Autosomal recessive traits require two copies of the recessive allele on an autosome; two carrier parents have a 25% chance in each pregnancy to have an affected child, a 50% chance to pass the recessive allele to the child, and a 25% chance to pass two dominant alleles.

Some traits are X-linked recessive, affecting mostly males because they have a single X chromosome. In such cases, a single recessive allele on the X chromosome can produce the trait in males, while females would require two copies.

Examples of recessive diseases in humans include cystic fibrosis, phenylketonuria (PKU), and sickle cell disease. It is important to note that not all recessive relationships are uniform; some genes exhibit incomplete dominance, where a heterozygote shows an intermediate phenotype, or codominance, where both alleles are fully expressed. The term rezessiven is used in various languages to describe this concept of recessive inheritance.