Correct Option: B. 100% tall Explanation: To understand why the correct answer is B (100% tall), we need to delve into basic genetics, specifically Mendelian inheritance, which explains how traits are passed from parents to offspring.

1. Understanding the Genes:
2. In this scenario, we have two alleles for the height trait in plants:
   • T: Represents the dominant allele for tallness.
   • t: Represents the recessive allele for dwarfness.
3. The tall plant is homozygous, meaning it has two identical alleles (TT), while the dwarf plant is homozygous recessive (tt).
4. Setting Up the Cross:
5. We are crossing a tall plant (TT) with a dwarf plant (tt).
6. The genotype of the tall plant is TT, and the genotype of the dwarf plant is tt.
7. Punnett Square:
8. To visualize the genetic cross, we can use a Punnett square. This is a simple diagram that helps predict the genotypes of the offspring.
9. The Punnett square for this cross would look like this:

``` T | T t | Tt | Tt t | Tt | Tt ```

• Each box in the Punnett square represents a possible genotype for the offspring. In this case, all offspring will have the genotype Tt.
• Interpreting the Results:
• The genotype Tt means that all offspring will express the tall phenotype because the tall allele (T) is dominant over the dwarf allele (t).
• Therefore, 100% of the offspring will be tall.

Why Other Options Are Incorrect:

• Option A: 100% dwarf:
• This option is incorrect because the dwarf phenotype (tt) can only occur if both alleles are recessive. Since all offspring from the cross are Tt, none can be dwarf.
• Option C: 50% tall and 50% dwarf:
• This option is incorrect because it suggests that there would be a mix of tall and dwarf plants. However, since all offspring are Tt, they will all be tall.
• Option D: 75% tall and 25% dwarf:
• This option is also incorrect. The 3:1 ratio typically applies to a cross between two heterozygous parents (Tt x Tt). In this case, since one parent is homozygous dominant (TT) and the other is homozygous recessive (tt), all offspring will be Tt and thus 100% tall.

Summary:

• The cross between a tall (TT) and a dwarf (tt) plant results in 100% tall offspring (Tt).
• The dominant allele (T) masks the effect of the recessive allele (t).
• Understanding dominant and recessive traits is crucial in predicting offspring characteristics.
• A Punnett square is a useful tool for visualizing genetic crosses and determining potential genotypes of offspring.