10. Two different mutant of Drosophilla gives a mutant black body color. When these mutants are crossed all progeny have wild type color, It means mutation are
(1) Codominant (2) Allelic
(3) Non Allelic (4) Epistatic
Concept
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Each parent fly is homozygous recessive for its own black‑body mutation.
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Crossing mutant 1 (gene a) with mutant 2 (gene b) gives progeny that are heterozygous at both loci (a⁺a bb⁺ or similar).
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Because each F₁ receives one functional (wild‑type) copy of each gene, pigment synthesis is restored and all offspring are wild type.
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This is the classic result of a complementation test: mutations in different genes complement and give wild type. Those are called non‑allelic mutants.
Option‑wise explanation
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Codominant
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Codominance means both alleles in a heterozygote are fully expressed (e.g., human AB blood group).
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Here, each mutant alone is recessive; the F₁ appears wild type, not a mixture of black and wild. This is not codominance.
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Allelic
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Allelic mutants affect the same gene.
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If both parents are homozygous for different recessive alleles of the same gene (a¹a¹ × a²a²), the F₁ (a¹a²) still lacks any wild‑type copy and would remain mutant (black).
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Because the cross gives wild type, the mutations are not allelic.
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Non allelic – correct
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Non‑allelic = in different genes.
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Each mutant has a defect in a different step of the same pathway; when combined, each supplies the wild‑type product missing in the other, so they complement and restore the wild‑type color.
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Epistatic
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Epistasis is interaction where one gene’s allele masks or modifies the effect of another gene in specific genotype combinations.
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While black body can involve epistatic interactions, the key observation here is full complementation (all F₁ wild). The defining conclusion from such a complementation test is that the mutations are in different genes, i.e., non‑allelic, not simply epistatic.
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Therefore, the two mutant black‑body strains are non‑allelic mutants that complement each other.
