Question

assume you are investigating the inheritance of stem length in pea plants. you cross-pollinate a short-stemmed plant with a long-stemmed plant. all of the offspring have long stems. then, you let the offspring self-pollinate. describe the stem lengths you would expect to find in the second generation of offspring.

a the f2 would have 50% long-stemmed plants and 50% short-stemmed plants.
b the f2 would have 25% long-stemmed plants and 75% short-stemmed plants.
c the f2 would have 75% long-stemmed plants and 25% short-stemmed plants.
d none of the above

Explanation:

Identify the parental genotypes and dominant trait

• Parental cross: True-breeding short-stemmed (\(tt\)) \(\times\) true-breeding long-stemmed (\(TT\))
• \(F_1\) offspring: All heterozygous long-stemmed (\(Tt\)), showing that long stem is dominant

Determine the F2 phenotypic ratio from self-pollination

• \(F_1\) self-cross: \(Tt \times Tt\)
• Genotypic ratio: \(1\ TT : 2\ Tt : 1\ tt\)
• Phenotypic ratio: \(75\%\) long-stemmed (\(TT, Tt\)) and \(25\%\) short-stemmed (\(tt\))

Answer:

• a The F2 would have 50% long-stemmed plants and 50% short-stemmed plants.
• b The F2 would have 25% long-stemmed plants and 75% short-stemmed plants.
• c The F2 would have 75% long-stemmed plants and 25% short-stemmed plants. (Correct answer)
• d None of the above