Question

In a garden pea plant, the flowers are in axial (A) position. Find out the proportion of flowers in terminal position (a), if a cross is made between two heterozygous plants.

Hint:

A heterozygous monohybrid cross always yields a 3:1 phenotypic ratio and 1:2:1 genotypic ratio.

Answer 1

Step 1: Identify the type of inheritance.
The position of flowers in garden pea shows a Mendelian monohybrid inheritance pattern.
• A = Axial flower position (dominant trait)
• a = Terminal flower position (recessive trait)

Step 2: Identify the genotype of the parents.
Both plants are heterozygous.
\[ \text{Genotype of parents: } Aa \times Aa \]

Step 3: Prepare the Punnett square.
Each parent produces two types of gametes: A and a.

Possible combinations:
AA, Aa, Aa, aa

Step 4: Determine the genotypic ratio.
The genotypic ratio obtained is:
\[ AA : Aa : aa = 1 : 2 : 1 \]

Step 5: Determine the phenotypic ratio.
• AA and Aa show axial flowers (dominant).
• aa shows terminal flowers (recessive).

Thus the phenotypic ratio is:
\[ \text{Axial : Terminal} = 3 : 1 \]

Final Answer:
The proportion of flowers in terminal position (a) is 1/4 or 25%.