In a dihybrid testcross involving two genes that assort independently ($AaBb \times aabb$), what is the expected phenotypic ratio among offspring?
Answer and explanation
Correct answer: D. 1 : 1 : 1 : 1
- Step 1: Testcross with homozygous recessive () reveals gamete frequencies of heterozygous parent. Step 2. Heterozygous parent produces gametes in equal 1:1:1:1 proportions. Step 3. Resulting offspring phenotypes appear in an equal ratio. Answer: Phenotypic ratio of 1 : 1 : 1 : 1. Why not the others: 9:3:3:1 is the ratio for an dihybrid cross ($AaBb \times AaBb$), not a testcross.
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