Question

A cross was carried out between a pure bred tall pea plant and a pure bred dwarf plant and F1 progeny was obtained. Later F1 progeny was self pollinated to obtained F2 plants. Answer the following:
a) What is the phenotype of F1 progeny
b) Why are the F2 progeny different from F1
c) Give the phenotypic ratio of F2 progeny

Answer 1

Pure breeding plants contain similar alleles in a pair (homozygous condition) for a particular trait.
On crossing pure breeding tall pea plant (TT) with pure breeding dwarf plant (tt).
Ans1) Plants of F1 generation are all tall.
Ans2) Ratio of tall plants to dwarf plants obtained in F2 generation is 3:1.
Ans3) Dwarf plants were not found in F1 generation, but appeared in F2 generation.
This occurred due to dominance of allele responsible for tallness (T) over recessive allele responsible for dwarfness (t) in a pea plant. The recessive alleles are expressed only in homozygous condition/similar alleles in pair (tt). The offspring obtained in F1 generation were all heterozygous (Tt), in that condition, dominant allele controlling the trait of tallness (T) overpowers the recessive allele(t). This is in accordance to law of dominance given by Mendel. This law explains expression of only one of the parental character in F ₁ generation and expression of both in F ₂ generation.