Principles of Genetics and Breeding (1+1)

2.1.2 Mendel's experiments

• The essence of his experiments was to cross breed plants that had discrete, non-overlapping characteristics and then to observe the distribution of these characteristics in the next several generations.
• He studied parental lines (P) of chosen plant. For 2 years he conducted experiments to get pure breed. He got pure line for each character of the 7 pairs by selfing for several generation. He got genetically pure tall and dwarf plants.
• The two pure lines were crossed and both strains were used as male and female parents.
• He recorded the results of F₁ and F₁ were selfed. He recorded the results of subsequent generation.
• He found that Tall, Round or Smooth seeds as dominant. Dwarf, wrinkled as recessive. Cotyledon colour, Yellow as dominant; Green as recessive.
• The expression of recessive character in F₁ is masked. But, when F₁ were selfed, the recessive character reappeared in F₂ offsprings in a definite ratio of 3:1. Among 4 plants of F₂ , 3 displayed dominant and 1 recessive characters. Mendel observed 787 tall (T) and 277 dwarf (t) plants for a ratio of 2.84 to 1. This 3:1 F₂ ratio was observed to occur in the monohybrid crosses for each of the 7 pairs of characters. When recessive F₂ were selfed in F₃ they produced only offsprings with recessive character.