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9:3:4 Recessive, 12:3:1 Dominant, 9:7 Complementary, 15:1 Duplicate
Picture This (Mental Hook): Imagine a modified casino board where 9:3:3:1 gets rearranged by gene interactions! When Recessive epistasis strikes, the last two slots merge (9:3:4 Labrador coat color). When Dominant epistasis strikes, the first two slots merge (12:3:1 Summer squash)!
📊 Visual Diagram & Mental Flow:
┌─────────────────────────┬──────────────┬────────────────────────────────────────────────────┐ │ Interaction Type │ F2 Ratio │ Classical Example │ ├─────────────────────────┼──────────────┼────────────────────────────────────────────────────┤ │ Mendelian Dihybrid │ 9:3:3:1 │ Independent assortment (Pea seed shape & color) │ │ Recessive Epistasis │ 9:3:4 │ Labrador retriever coat (ee masks B black / b brown│ │ Dominant Epistasis │ 12:3:1 │ Fruit color in Summer squash (Cucurbita pepo) │ │ Duplicate Recessive │ 9:7 │ Flower color in Sweet Pea (Lathyrus odoratus) │ │ (Complementary Genes) │ │ (Both enzymes needed for purple anthocyanin) │ │ Duplicate Dominant │ 15:1 │ Seed capsule shape in Shepherd's purse (Capsella) │ │ Dominant & Recessive │ 13:3 │ Feather color in fowl (Inhibitory gene interaction)│ └─────────────────────────┴──────────────┴────────────────────────────────────────────────────┘
🔍 The Decoded Sequence:
9:3:4
Recessive Epistasis
Homozygous recessive at one locus masks expression of both alleles at second locus
12:3:1
Dominant Epistasis
Dominant allele at one locus produces phenotype regardless of second locus
9:7
Complementary Genes
At least one dominant allele at BOTH loci required for wildtype phenotype
Examiner Trap / Never Forget: Notice that in ALL epistatic modifications, the sum of the ratio numbers ALWAYS equals 16 (e.g. 9+3+4=16; 12+3+1=16; 9+7=16; 15+1=16)!
