Final answer:
Mendel's first-generation offspring were all tall when he crossed a tall with a short pea plant. In the second generation, 75% were tall and 25% were short, reflecting a dominant trait for tallness with a typical 3:1 phenotypic ratio in a monohybrid cross. option b is correct.
Step-by-step explanation:
When Mendel crossed a tall pea plant with a short pea plant, the first generation of offspring (F1) were always tall. When Mendel crossed the F1 generation offspring with each other, the distribution was about 75% tall and 25% short. The correct completion of the statements is option b) Tall – 75 – 25.
This is because tallness is the dominant trait, and in the F2 generation following a Mendelian monohybrid cross, a phenotypic ratio of approximately 3:1 is expected based on the principle of random segregation.
The Punnett square would show that the genotype ratio for homozygous dominant (TT), heterozygous (Tt), and homozygous recessive (tt) would be 1:2:1, respectively, but phenotypically, since TT and Tt individuals exhibit the same tall characteristic, the ratio simplifies to 3:1 for tall to short plants.