Law of Segregation

After having obtained several generations of
plants by self-fertilization, Mendel observed that the descendants are similar to their parents, constituting what were later called pure lines.
For the beginning of the crosses, he used homozygous plants, with a single contrasting character, which involved a pair of alleles, that is, he made a monohybrid cross. The seven characters he selected have two expressions, one of them behaves as dominant and the other as recessive. To represent the dominant character he used capital letters and for the recessive, lowercase letters.
Thus, for example, in the parental generation represented by plants of a pure line in the form of the sheath, those with smooth sheath are homozygous dominant (AA) and those with rough sheath are homozygous recessive (aa); when producing gametes, they have only one factor: A or a.
When the gametes are fertilized they originate the first filial generation (F1), formed by heterozygous genotypes (Aa); phenotypically (that is, the expressed genes) are all the same and show the dominant character: smooth sheath, so the rough sheath character disappears in this generation.

A = smooth sheath A = rough sheath

Outcome = Genotype = 100% A / a
Phenotype = 100% smooth pods
Interpretation = All are heterozygous, and the dominant character is manifested.
He self-pollinated the F1 generation plants and obtained a second filial generation (F2), in which the originally crossed characters reappear: smooth pods and rough pods.
The recessive character that had disappeared in F1 only remained hidden for a generation. And also in this new generation (F2), the smooth and rough phenotypes manifested in a defined proportion:

Outcome =
Genotype:% A / A; V * A / a and% a / a.

Phenotype: 75% smooth pod; 25% rough sheath
Interpretation = Homozygous A / A are logically expressed as smooth sheath; heterozygotes are expressed as a smooth sheath because this is a dominant character and homozygous a / a are expressed as a rough sheath because, despite being recessive, they are two identical genes.
As a result of these observations, Mendel established the law of segregation which says: By crossing two individuals who differ in only one character, during the formation of its gametes the pair of genes responsible for each character is separated, so that each gamete contains only one allele for that character.
Of the alleles, one form of the inherited trait is dominant and prevents the expression of the recessive trait.