Monohybrid Cross Genotypic Ratio

Steps:

• Cross two heterozygous plants: Aa × Aa for one trait.
• Each parent produces gametes: 50% A and 50% a.
• Punnett square shows offspring: 25% AA, 50% Aa, 25% aa.
• Homozygous (AA + aa) total 50%, heterozygous (Aa) 50%, ratio 1:2.

Why A is correct:

• Mendel's 1:2:1 genotypic ratio combines homozygous classes (1+1=2 parts) against heterozygous (2 parts), yielding 1:2.

Why the others are wrong:

• B: Duplicate of correct ratio but not the specified option.
• C: 3:1 is the phenotypic ratio for dominant:recessive traits, not homozygous:heterozygous genotypes.
• D: Duplicate of incorrect phenotypic ratio.

Final answer: A