The understanding about inherited traits or the physical characteristics passing between generations was proposed by Gregor Mendel.
Mendel's key principles of genetics were based on his studies and experiments of the characteristics or traits of the pea plants.
According to his fundamental theory of heredity he concluded that inheritance occurs by passing of discrete units of inheritance from the parents to the offspring and these discrete units were called genes.
When the parent pea plants were crossed the trait that appeared was termed as dominant trait and the trait that remained hidden in the first generation offspring was termed as recessive trait. The recessive trait appeared in the successive generations.
The physical appearance that was observed like height, colour and shape of seeds etc was termed as phenotype. The phenotype that appeared was due to the genotype that was expressed and genotype is the genetic makeup of any organism.
According to Mendel, one gene controls one character and each trait is inherited independently. Multiple forms of the genes are called as alleles and represent a particular characteristic. Example: one allele would represent tall plant while other would represent a short plant.