When Mendel crossed a plant homozygous for round seeds to another plant homozygous for wrinkled seeds, he found that all the progeny had round seeds. How is this explained?
A) The parent that was homozygous for round seeds underwent self‑pollination.
B) The allele for round seeds is recessive to the allele for wrinkled seeds.
C) The progeny were homozygous for the allele for round seeds.
D) Segregation of alleles in the two parents produced gametes with both alleles.
E) The allele for round seeds is dominant to the allele for wrinkled seeds.

Gregor Mendel discovered the principles that governs heredity. In one of his experiments, he discovered that an organism receives two forms of a gene called ALLELE from each parent. He realized that one allele is capable of masking the expression of its variant pair in a gene. He called the allele that masks or is expressed, DOMINANT allele while the allele that is masked, RECESSIVE allele. He termed this principle the LAW OF DOMINANCE.

The above explained law of dominance is what applies in the question here. When the homozygous round allele and wrinkled allele were crossed, the allele for round seeds are dominant over the allele for wrinkled seeds (recessive) i.e. in a heterozygous state (combination of the different alleles), the round allele will mask the phenotypic expression of the wrinkled allele, expressing itself over it.