GENE20001 Lecture Notes - Lecture 9: Penetrance, Epistasis, Mutation
White 1 x white 2 - F1 all white. Mutations in same gene
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White 1 x white 3 - F1 all blue. Mutations in different genes
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White 2 x white 3 - F1 all blue. Mutations in different genes
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Mutants 1 and 2 have different alleles of one gene; mutant 3 has mutation in a
different gene.
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determine if mutant strains affected in same or different genes.
Other types of gene interaction can most easily be explained by considering biochemical
pathways.
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Genes affect the same phenotype but operate in different pathways
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Mutations in any of the genes alter the pigmentation
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Mutation in 1, 2, 3 results in overall yellow phenotype; mutation in 4, 5, 6 results in
overall red phenotype; double homozygous mutant produces a novel phenotype,
colourless
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Synthetic phenotypes
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Divergent pathways can lead to epistasis: where one gene masks the phenotypic
expression of another gene
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These indicate the mutations and the resulting phenotype
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A double mutant shows mutation in gene 1 but not the mutation. Gene 2 or 5 could
mutate and we wouldn't know
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Epistatic = overriding mutation; hypostatic = overridden mutation
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Genes in the same pathway: epistatic mutation is carried by a gene that is farther
upstream than the gene of the overridden mutation
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9:3:3:1 ratio: no gene interaction
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Epistasis
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Genetics Page 6
Document Summary
Determine if mutant strains affected in same or different genes. White 1 x white 3 - f1 all blue. White 2 x white 3 - f1 all blue. Mutants 1 and 2 have different alleles of one gene; mutant 3 has mutation in a different gene. Other types of gene interaction can most easily be explained by considering biochemical pathways. Genes affect the same phenotype but operate in different pathways. Mutations in any of the genes alter the pigmentation. Mutation in 1, 2, 3 results in overall yellow phenotype; mutation in 4, 5, 6 results in overall red phenotype; double homozygous mutant produces a novel phenotype, colourless. Divergent pathways can lead to epistasis: where one gene masks the phenotypic expression of another gene. These indicate the mutations and the resulting phenotype. A double mutant shows mutation in gene 1 but not the mutation. Gene 2 or 5 could mutate and we wouldn"t know.
