To solve this question, we need to understand the basics of monohybrid crosses and the resulting phenotypic ratios in the [tex]$F_2$[/tex] generation.
A monohybrid cross is a mating between two individuals with different alleles at one genetic locus of interest. The classic example is Mendel’s peas, where he looked at a single trait, such as plant height.
### Step-by-Step Solution:
1. Understanding Monohybrid Crosses:
- Suppose we consider two plants that are heterozygous for a dominant trait (e.g., T for tall and t for short). These plants would have the genotype Tt.
- When these heterozygous plants are crossed (Tt x Tt), the resulting offspring (F2 generation) can have the following genotypes: TT, Tt, tT, and tt.
2. Phenotypic Ratio Analysis:
- The dominant trait will be expressed if at least one dominant allele (T) is present.
- The recessive trait appears only when both alleles are recessive (tt).
- So, we can group the potential genotypes as follows:
- TT (tall)
- Tt (tall)
- tT (tall)
- tt (short)
- Among these four groups, TT, Tt, and tT will all exhibit the dominant phenotype (tall), while tt will exhibit the recessive phenotype (short).
3. Counting the Phenotypes:
- There are three possible ways to get the dominant phenotype (TT, Tt, tT).
- There is one possible way to get the recessive phenotype (tt).
4. Calculating the Ratio:
- This results in a 3:1 ratio of dominant (tall) to recessive (short) phenotypes.
5. Conclusion:
- The question asks for the phenotypic ratio of the recessive trait reappearing in the F2 generation.
From this analysis, we find the ratio of tall to short plants in the [tex]$F_2$[/tex] generation is [tex]$\boxed{3:1}$[/tex].
