Which of the following are reasons for Mendel’s success?
(i) Usage of pure lines or pure breeding varieties
(ii) Consideration of one character at a time in the initial experiments
(iii) Maintenance of statistical records of experiments
(iv) Knowledge of incomplete dominance

The correct option is B (i), (ii) and (iii)
Mendel while conducting experiments on pea plants used pure breeding varieties.
A pure breeding variety is one that shows the stable trait inheritance and expression because of having undergone continuous self-pollination for several generations.

He initially considered one character at a time for his studies and recorded the observation and results.

He used statistical analysis and mathematical logic to understand and prove biological phenomena.

He was not aware of the concept of incomplete dominance in which the alleles controlling a character blend and produce intermediate phenotypes in the hybrid. Mendel believed that the genes (or factors, in Mendel’s words) were stable and discrete units that controlled the expression of traits and did not ‘blend’ with each other.