All the offspring of a cross between a tall pea plant and a dwarf pea plant are tall. this means that the allele for tall plants is the allele for dwarf plants.

All the offspring of a cross between a tall pea plant and a dwarf pea plant are tall. This means that the allele for tall plants is DOMINANT OVER the allele for dwarf plants.

Explanation:

Mendel's law of dominance state that the heterozygous genotype expresses only one allele of a gene out of the two alleles present together. The allele that is expressed in a heterozygous genotype is said to be the dominant one as it does not allow the expression of another allele of the gene.

The allele of a gene that is not expressed in the presence of its dominant allele is said to be the recessive one. Under such conditions, a heterozygous genotype expresses the dominant phenotype. When a tall and dwarf pea plants are crossed, all the F1 progeny is tall. This means that the allele for the tallness is dominant over the allele for the dwarfism.