According to Mendelian genetics, what is the phenotypic ratio in the F2 generation of a monohybrid cross between two heterozygous individuals ()?
Answer and explanation
Correct answer: A. 3 : 1
- Step 1: Set up a Punnett square for : genotypes produced are , , and .
- Step 2: Because allele is completely dominant over allele , individuals with and display the dominant phenotype (3 parts), while displays the recessive phenotype (1 part), yielding a phenotypic ratio.
Answer
3 : 1.
Why not the others: '1 : 2 : 1' is the genotypic ratio (); '9 : 3 : 3 : 1' is the phenotypic ratio of a dihybrid cross ($AaBb \times AaBb$); '1 : 1' is the ratio from a test cross of a heterozygote with homozygous recessive.
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