Which of the following statements is incorrect?      

i) Genes that code for a pair of contrasting traits are known as alleles, i.e., they are slightly different forms of the same gene.
ii) T is used for the tall trait and t for the ‘dwarf’ and T and t are alleles of each other.
iii) Allele may be homozygous, TT and tt, or heterozygous Tt.
iv) To determine the genotype of a tall plant, Mendel crossed the tall plant with a dwarf plant.
v) In a typical test crossing, an organism showing a dominant phenotype is crossed with any parent instead of self-crossing.
vi) Based on his observations on monohybrid crosses, Mendel proposed three general rules.