Question

A cross was carried out between a pure bred tall pea plant and a pure bred dwarf pea plant and F1 progeny was obtained. Later, the F1 progeny was selfed to obtain F2 progeny. Answer the following questions :
a. What is the phenotype of the F1 progeny and why?
b. What is the phenotype of the F2 progeny and why?
c. Give the phenotype ratio of the F2 progeny.
d. Why is the F2 progeny different from the F1 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.