Question

In monohybrid cross, the phenotypic ratio for $F_2$ generation is

• A. 1 : 3
• B. 3 : 1
• C. 1 : 2 : 1
• D. 2 : 1 : 1

Answer 1

The correct option is B 3 : 1

• The monohybrid cross involves the cross between plants considering only one trait. A cross between pure breeding tall (TT) and dwarf (tt) varieties gives all heterozygous tall (Tt) progeny in $F_1$ generation.
• Selfing of $F_1$ hybrid gives tall and dwarf $F_2$ progeny in 3: 1 ratio respectively. Since allele for tallness (T) is dominant over that of dwarfism (t), both homozygous dominant (TT) and heterozygous dominant (Tt) exhibit tall phenotype while homozygous recessive genotype gives dwarf phenotype; hence phenotypic ratio is 3 tall: 1 dwarf but the genotypic ratio is 1 TT: 2 Tt: 1 tt.

Thus, the correct answer is option B.