Resessiivi

Resessiivi, the Finnish term for recessive, describes an allele or trait that requires two copies to be expressed in a diploid organism. A single resessiivi allele paired with a dominant allele typically does not produce the recessive phenotype; the dominant allele masks it. Only when two copies of the recessive allele are present (homozygous recessive) is the trait usually visible.

In individuals with two recessive alleles, the recessive trait is visible. Heterozygotes are typically carriers and do not show the trait but can pass the allele to offspring.

Inheritance patterns: For autosomal recessive traits, males and females are affected roughly equally. Two carrier parents have a 25% chance with each pregnancy to have an affected child, a 50% chance to have a carrier child, and a 25% chance to have a non-carrier child.

Examples: Diseases such as cystic fibrosis, phenylketonuria, and Tay-Sachs disease are commonly cited recessive disorders. Across populations, the frequency of recessive conditions depends on the carrier rate; some recessive alleles persist due to selective advantages in carriers, as in sickle cell trait offering malaria resistance.

In population genetics, if p is the frequency of the dominant allele and q is the frequency of the recessive allele, Hardy-Weinberg equilibrium gives genotype frequencies as p^2 (homozygous dominant), 2pq (heterozygous), and q^2 (homozygous recessive).

X-linked recessive patterns differ: females are typically carriers while affected individuals are often male because of their single X chromosome.