Law of dominance: characters are controlled by discrete units called factors (genes) which occur in pairs; in a dissimilar pair (heterozygous) of factors, one factor is dominant and expresses itself while the other is recessive and remains masked. Law of segregation: during the formation of gametes, the two factors (alleles) of a pair separate (segregate) so that each gamete receives only one factor of the pair; the factors do not blend and are passed on unchanged.

Mendel's law of independent assortment states that when two pairs of contrasting characters (traits) are considered together, the alleles of one pair of characters segregate (assort) independently of the alleles of the other pair during the formation of gametes. In other words, the inheritance of one character is not affected by the inheritance of another. This law is based on the results of a dihybrid cross, which gives a phenotypic ratio of 9 : 3 : 3 : 1 in the F2 generation.

A test cross is a cross in which an individual showing a dominant phenotype (whose genotype is unknown) is crossed with a homozygous recessive individual. It is used to determine whether the individual with the dominant phenotype is homozygous or heterozygous. If all the offspring show the dominant character, the individual is homozygous; if the offspring show a 1 : 1 ratio of dominant to recessive phenotypes, the individual is heterozygous.