In a dihybrid cross, what is the expected phenotypic ratio in the F2 generation?
Practice Questions
Q1
In a dihybrid cross, what is the expected phenotypic ratio in the F2 generation?
3:1
1:2:1
9:3:3:1
1:1:1:1
Questions & Step-by-Step Solutions
In a dihybrid cross, what is the expected phenotypic ratio in the F2 generation?
Correct Answer: 9:3:3:1
Step 1: Understand what a dihybrid cross is. It involves two traits, each with two alleles.
Step 2: Identify the parental generation (P generation) with two traits. For example, let's say we have tall (T) vs. short (t) plants and yellow (Y) vs. green (y) seeds.
Step 3: Cross the two parental plants to create the first generation (F1). All offspring will be heterozygous for both traits (TtYy).
Step 4: In the F1 generation, perform a self-cross (TtYy x TtYy) to create the second generation (F2).
Step 5: Use a Punnett square to determine the combinations of traits in the F2 generation. You will have 16 possible combinations.
Step 6: Count the phenotypes (observable traits) from the combinations. You will find 9 with both dominant traits, 3 with the first dominant and second recessive, 3 with the first recessive and second dominant, and 1 with both recessive traits.
Step 7: Write down the expected phenotypic ratio: 9 (dominant-dominant) : 3 (dominant-recessive) : 3 (recessive-dominant) : 1 (recessive-recessive).
