A trihybrid plant with genotype is testcrossed ($AaBbCc \times aabbcc$). Assuming all three gene loci assort independently, what is the expected phenotypic ratio of the offspring?
Answer and explanation
Correct answer: A.
- Step 1: In a trihybrid individual (), the three independently assorting heterozygous gene pairs each produce two types of gametes with equal probability: distinct gamete genotypes.
- Step 2: The homozygous recessive tester () produces only one gamete genotype ().
- Step 3: Combining the 8 maternal gamete types with the tester gamete produces 8 distinct phenotypic classes in an equal ratio of .
Answer
(eight equal phenotypic classes).
Why not the others: is the phenotypic ratio of a dihybrid self-cross; is the phenotypic ratio of a trihybrid self-cross ($AaBbCc \times AaBbCc$); is the genotypic ratio of a dihybrid cross.
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