Epistasis.docx

When one gene masks or effects the phenotype of another. Referred to interaction between different genes, not between the alleles of the same gene. Epistasis only effects the phenotypic ratios Gene that affects the expression of the other is called a modifier gene (epistatic gene) The blocked gene i...

When one gene masks or effects the phenotype of another. Referred to interaction between different genes, not between the alleles of the same gene. Epistasis only effects the phenotypic ratios Gene that affects the expression of the other is called a modifier gene (epistatic gene) The blocked gene is expressed normally, but the product of the modifier gene. Inactivates it. Counteracts its effects. Removes it from structure needed for phenotype. Types of epistasis Recessive epistasis Homozygous recessive at one locus prevents the other locus from exerting its phenotype. e.g. ABO blood grouping 9:3:3:1 modified to 9:3:4 Dominant epistasis Dominant allele at one locus prevents other locus from exhibiting the homozygous recessive phenotype. 9:3:3:1 modified to 12:3:1 Dominant and recessive epistasis A dominant allele at one locus produces the same phenotype as the homozygous recessive at the other locus. 9:3:3:1 ratio modified to 13:3 Duplicate recessive epistasis When either locus is homozygous recessive, it masks the dominant effect at the other locus. 9:3:3:1 ratio is modified to 9:7 Duplicate dominant recessive epistasis The presence of a dominant allele at either of two loci produces the dominant phenotype. Products from either A or B gene performs the same function. 9:3:3:1 ratio is modified to 15:1 Duplicate gene epistasis with cumulative effect When the dominant allele at either locus, but not both, produces the same phenotype. Expression level of proteins produced by genes A and B is important for phenotype.