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Very few phenotypes are purely Mendelian traits. Common violations of the Mendelian model include incomplete dominance, codominance, genetic linkage, environmental effects, and quantitative contributions from a number of genes (see: gene interactions, polygenic inheritance, oligogenic inheritance). [1] [2]
Incomplete dominance (also called partial dominance, semi-dominance, intermediate inheritance, or occasionally incorrectly co-dominance in reptile genetics [13]) occurs when the phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The phenotypic result often appears as a ...
In genetics, the partial dominance hypothesis states that inbreeding depression is the result of the frequency increase of homozygous deleterious recessive or partially recessive alleles. The hypothesis can be explained by looking at a population that is divided into a large number of separately inbred lines.
Autosomal dominant A 50/50 chance of inheritance. Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition. [1]
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.
Under the law of dominance in genetics, an individual expressing a dominant phenotype could contain either two copies of the dominant allele (homozygous dominant) or one copy of each dominant and recessive allele (heterozygous dominant). [1] By performing a test cross, one can determine whether the individual is heterozygous or homozygous ...
In population genetics, directional selection is a type of natural selection in which one extreme phenotype is favored over both the other extreme and moderate phenotypes. This genetic selection causes the allele frequency to shift toward the chosen extreme over time as allele ratios change from generation to generation.
In order for the a phenotype to become active, the gene must end up as homozygous aa because in the geneotype Aa, the A takes dominance over the a and the a does not have any effect. Some recessive genes result in detrimental phenotypes by causing the organism to be less fit to its natural environment.