Final answer:
Particulate unit factors are also known as genes, which come in different forms called alleles that can be dominant or recessive. Mendel’s experiments with pea plants revealed how these genes are passed from parents to offspring, establishing the basic principles of heredity and the understanding of dominance and recessiveness in genetics.
Step-by-step explanation:
Particulate unit factors are another term for what we now refer to as genes. The foundational work of Gregor Mendel on pea plants led to the discovery that these factors are responsible for the transmission of heritable traits from parents to offspring. Each trait is controlled by a pair of genes, one inherited from each parent. Mendel recognized that these genes come in different varieties, which we call alleles. Some of these alleles can be dominant or recessive.
The Law of Dominance explains how in the presence of a dominant allele, the trait it controls will be expressed, whereas a recessive allele's trait will only be evident in the absence of a dominant allele. This mechanism illustrated why certain traits might not appear in one generation but would reemerge in the next. For example, when Mendel crossed a tall pea plant (dominant trait) with a short pea plant (recessive trait), all F1 offspring were tall, but the F2 generation exhibited both tall and short plants in a 3:1 ratio.
Ultimately, the units of heredity Mendel referred to are now understood to be genes located on chromosomes, with alleles representing the variant forms of these genes that determine the genotype and phenotype of an individual. This discovery marks the beginning of classical genetics and our understanding of inheritance and genetic variation.