Explanation

3:1 ratio in F2-generation explained by law of dominance Principle of law of dominance state that only dominant allele shows its effect evan in the heterozygous condition. Law or Principle of Dominance In heterozygous individuals or hybrids a character is represented by two contrasting factors called alleles or allelomorphs. Out of the two contrasting alleles. Only one is able to express its effect in the individual. It is called dominant factor or dominant allele. The other which does not show its effect in the heterozygous individual is called recessive factor or recessive allele. The cross between the pure tall and pure dwarf gives all progeny (F1) tall. The character shown by F1 called dominant character Mendel cross-pollinated a pure tall pea plant (100-120 cm hight) and a pure dwarf pea plant. (only 22 to 44 cm hight). He called them parental generation, expressed now-a-days by symbol P. This hybridization popularly called as monohybrid cross This three generations of pea plants after crossing a pure tall plant with a dwarf one. The plants of F1-generation are all tall, of F2-generation three tall and one dwarf. One third of the tall plants are pure, while the remaining behave as hybrids F1-generation Seeds collected from the parental generation called first filial generation or F1-generation F2-generation F1-plants pollinated among them self (self breeding or inbreeding) and seed produced by F1-plants called F2-generation. They were in ratio 3:1 (three tall and one dwarf). F3-generation Mendel allowed F2-plant to form seed by self-pollination called F3-generation. Mendel observed that tall and dwarf plant behave differently (i) Dwarf plant produced dwarf plant on self-pollinated (ii) In tall plants one third plants breed true so they were pure (iii) Other two third plant behave like parents and give tall to dwarf plants 3 : 1 indicate that their parents have dwarf genes also