Final answer:
Mendel's work showed that traits are inherited through genes in discrete units called alleles, with dominant and recessive patterns. Each parent contributes one allele per gene, affecting an individual's genotype and phenotype.
Step-by-step explanation:
Gregor Mendel concluded that traits are inherited through the passing of factors we now call genes from parents to offspring. Using his groundbreaking work on pea plants, Mendel discovered that these hereditary factors are transmitted in discrete units, now known as alleles, which can be either dominant or recessive. He identified that each parent contributes one allele per trait to their offspring. Mendel's experiments led to the understanding that the genotype, which is the combination of alleles an individual has, determines the phenotype, the observable traits. Through his crossing experiments, he notably observed the 3:1 ratio in the F2 generation, demonstrating that recessive traits can reappear after being masked by dominant traits in heterozygous individuals.