A.Dominance relationship - a relationship between alleles of one gene, in which effect on phenotype of one allele masks contribution of a second allele at same locus. The first allele is dominant and second allele is recessive.

B.Particulate inheritance -  inheritance of discrete characters via genes that are independently expressed without blending of characters from one generation to next generation.

C.Monogenic inheritance ? inheritance, involves transfer of a character by involvement of a single gene. It produces only one type of phenotypes.

D.Polygenic inheritance - inheritance, involves transfer of a character by involvement of a more than one gene. It produces multiple phenotypes.

Random mutations are ultimate source of genetic variation. Mutations are likely to be rare and most mutations are neutral or deleterious, but in some instances, new alleles can be favoured by natural selection.