Epistasis Flashcards
The different types of epistasis
Dominant epistasis
○A dominant allele at one locus prevents the expression of the other locus (Klug et al., 2020, pp. 110).
○Due to the presence of an inhibitor which interferes with the phenotype.
○A_B_ = aaB_
○12:3:1 ratio
Reference: Klug, W.S., Cummings, M.R., Spencer, C.A., Palladino, M.A., Killian, D.J. (2020) Concepts of Genetics. 12th rev. edn. Harlow: Pearson Education.
Recessive epistasis
○The absence of something interferes with the phenotype.
○This occurs due to a homozygous recessive allele at one locus preventing the expression of another locus.
○wwmm = wwM_
○9:3:4 ratio
Duplicate genes with cumulative effect
○When either locus, bot not both, has a dominant allele, the same phenotype is expressed.
○This is because both genes express the same gene products, but the amount of protein expressed is important for the phenotype, called gene dosage.
○Dominant alleles at both loci (A_B_) produce too much protein, and thus have a different phenotype.
○A_bb = aaB_ (A_B_ & aabb are different)
○9:6:1 ratio
Duplicate dominant epistasis
○D allele at either loci produces dominant phenotype.
○This is because gene A and gene B express products which perform the same functions.
○A_B_ = A_bb = aaB_ (aabb is different)
○15:1 ratio
Duplicate recessive epistasis
○rr at either locus masks dominant effect at other locus.
○A_bb = aaB_ = aabb (A_B_ is different)
○9:7 ratio
Dominant and recessive epistasis
○The expression of one allele is concealed, regardless of whether it is dominant or recessive, due to the dominant effects of the other allele.
○A_B_ = A_bb = aabb (aaB_ is different)
○AAB_ = AaB_ = aaB_ (A_bb is different)
○13:3 ratio
Describe epistasis.
○Epistasis is when a gene affects another genes expression or phenotype.
Describe what a modifier or epistatic gene is.
○A modifier, or epistatic, gene affects another genes expression.
Describe how a modifier gene affects the blocked gene.
○The modifier gene may inactivate the blocked gene, or counteract its effects.
○It may also remove a structure or metabolite which is needed for the phenotype.
