Question

in the f₂ generation of mendel’s crosses, all plants had the dominant trait. half of the plants had the dominant allele. all plants had both the dominant and recessive alleles. one in four plants had two alleles for the recessive trait.

Explanation:

Mendel's \( F_2 \) generation from a monohybrid cross (e.g., tall vs short plants) has a genotypic ratio of \( 1:2:1 \) (homozygous dominant : heterozygous : homozygous recessive) and phenotypic ratio \( 3:1 \) (dominant : recessive). So, \( \frac{1}{4} \) plants are homozygous recessive (two recessive alleles). Other options are incorrect: not all have dominant trait, "half with dominant allele" is wrong (heterozygotes and homozygous dominant have dominant allele, more than half), and not all have both alleles (homozygous have one type).

Answer:

D. one in four plants had two alleles for the recessive trait (assuming the options are labeled A - D as per typical multiple - choice, with the last option being the correct one)