In addition to the effects of different alleles of a gene at a single locus, alleles of different genes at different loci might influence each other and that might be expressed in the phenotype of the trait they influence. Again we have two possibilities: the effects of different alleles at different loci are additive: the effect is the sum of the effect of the individual alleles.
When these effects are non-additive, this is called epistasis. Epistasis is when loci are non-additive. The genotypic value of a locus on a trait depends upon the genotypes at other loci or a situation in which the differential phenotypic expression of a genotype depends on the genotype at another locus. Plumage pattern in chicken is amongst other genes, determined by interacting alleles of two different loci: the E-locus and the S-locus. The S-locus: S and s.
In the non-black parts of the plumage the SS or Ss animals have at these places the silver colour, while the ss animals have there the golden colour. Quick Search. Hit enter to search. Animal breeding. Expand all Collapse all. A t tachments 0 Page History People who can view. Skip to end of banner.
Jira links. Delete Cancel. The two chromosomal copies alleles of a gene are designated A and a. In most cases, both alleles are transcribed; this is known as bi-allelic expression left. However, a minority of genes show monoallelic expression right. In these cases, only one allele of a gene is expressed right. Which of the two alleles is expressed may be determined by the parental origin of the allele such as in imprinting.
Alternatively, the choice may be random. This image is linked to the following Scitable pages:. When only one allele of a gene is actively transcribed, gene expression is termed monoallelic. What does monoallelic gene expression have to do with cats, twins, and genetic diseases? Comments Close. Alleles contribute to the organism's phenotype, which is the outward appearance of the organism. Some alleles are dominant or recessive. When an organism is heterozygous at a specific locus and carries one dominant and one recessive allele, the organism will express the dominant phenotype.
Alleles can also refer to minor DNA sequence variations between alleles that do not necessarily influence the gene's phenotype. Further Exploration Concept Links for further exploration gene recessive dominant test cross genotype phenotype haplotype DNA chromosome Hardy-Weinberg equilibrium evolution mutation speciation penetrance SNP allele frequency Hardy-Weinberg equation population bottleneck principle of segregation principle of independent assortment dihybrid cross genetic drift lethal allele principle of uniformity Principles of Inheritance.
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