Mendel's experiments showed that:
All traits are determined by multiple genes
Recessive traits are always expressed in offspring
Dominant traits are always expressed in offspring
The expression of traits can be influenced by the environment
Studies have shown that even when a recessive gene is present, a dominant allele will still manifest in the progeny. This is because the expression of the recessive gene is concealed by the dominant allele. For instance, if a pea plant possesses both a dominant gene for yellow seeds and a recessive allele for green seeds, the dominant allele for yellow seeds will be expressed, resulting in yellow seeds on the plant. However, if a plant possesses two green seed-producing recessive alleles, green seeds will result because no dominant allele can prevent the expression of the recessive allele. As a result, Mendel's tests showed that recessive traits can only be expressed when both alleles are recessive, whereas dominant traits are always expressed in offspring.
Option 3 is the correct answer.