page_title: Non-Mendelian inheritance
section_title: Epistasis
hierarchical_section_title: Non-Mendelian inheritance / Types / Epistasis
caption_attribution_description: English: Cat, FoP-Czech Republic
context_page_description: Non-Mendelian inheritance is any pattern of inheritance in which traits do not segregate in accordance with Mendel's laws. These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. If the genotypes of both parents in a genetic cross are known, Mendel's laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values.
  Non-Mendelian inheritance plays a role in several disease processes.
context_section_description: If one or more genes cannot be expressed because of another genetic factor hindering their expression, this epistasis can make it impossible even for dominant alleles on certain other gene-loci to have an effect on the phenotype. An example in dog coat genetics is the homozygosity with the allele "e e" on the Extension-locus making it impossible to produce any other pigment than pheomelanin. Although the allele "e" is a recessive allele on the extension-locus itself, the presence of two copies leverages the dominance of other coat colour genes. Domestic cats have a gene with a similar effect on the X-chromosome.
caption: In the genepool of cats (Felis silvestris catus) there is a recessive allele for orange coat on the X-Chromosome. In a male the Y-Chromosome cannot compensate this, so a hemizygous tomcat is born orange. This allele is epistatic over some other coat color genes.[4][5]
exif: {"Image Orientation": "Horizontal (normal)"}