SB 4: Extensions to Mendel’s Laws

genotypic classes

a grouping defined by a set of related genotypes that will produce a particular phenotype. The term is most useful in describing progeny of dihybrid or multihybrid crosses involving complete dominance; for example, in a cross between Aa Bb individuals, the genotypic classes are A- B-, A- bb, aa B-, and aa bb.

epistasis

a gene interaction in which the effects of alleles at one gene hide the effects of alleles at another gene.

• gene doing the masking = epistatic

• gene that’s being masked = hypostatic

recessive epistasis

a gene interaction in which the effects of recessive alleles at one gene hide the effects of alleles at another gene.

• tell-tale ratio of recessive epistasis in F2 generation = 9:3:4

reciprocal recessive epistasis

dominant epistasis

a phenomenon where the effects of a dominant allele at one gene hide the effects of alleles at another gene.

• 12:3:1

redundant gene action/reciprocal dominant epistasis

a phenomenon where dominant, functional alleles of either one or the other of two genes is required in a pathway.

heterogeneous trait

a characteristic caused by a mutation in any one of a number of different genes

complementation test

method of discovering whether two mutations are in the same or separate genes. Two mutant strains with the same (or similar) mutant phenotype are crossed. If the progeny are all wild type (complementation occurred), the strains had mutations in different genes; if the progeny are all mutant (no complementation occurred), the strains had mutations in the same gene.