60. A plant with orange flowers was self-pollinated. In the F1 progeny, we obtained 38 plants producing red
flowers, 80 plants producing orange flowers and 41 plants producing yellow flowers. The likely explanation
for the above observation is that:
a. the gene for flower colour shows incomplete dominance.
b. flower colour is a polygenic trait controlled by 3 genes.
c. the gene for flower colour is epistatic to another gene.
d. the trait of flower colour is maternally inherited.

🌱 Introduction

Genetics is fascinating, especially when flower colors reveal deeper principles of inheritance. In a study where a plant with orange flowers was self-pollinated, the F1 progeny produced:

• 38 red-flowered plants

• 80 orange-flowered plants

• 41 yellow-flowered plants

Let’s explore which genetic mechanism explains this distribution best.

🔍 Analyzing the Observation

Given Data:

• Total F1 plants = 38 + 80 + 41 = 159

• The ratio of Red:Orange:Yellow ≈ 1:2:1

This 1:2:1 phenotypic ratio is highly characteristic of a Mendelian monohybrid cross showing incomplete dominance, where:

• RR = Red

• Rr = Orange

• rr = Yellow

The heterozygous Rr (orange) plant self-pollinates:

Rr × Rr → RR, Rr, Rr, rr
Resulting in:
1 Red : 2 Orange : 1 Yellow

✅ Correct Answer:

a. The gene for flower colour shows incomplete dominance.

🧬 What is Incomplete Dominance?

Incomplete dominance is a type of inheritance where:

• Neither allele is completely dominant over the other.

• The heterozygote exhibits a blended phenotype.

🔴 Example:

• RR = Red flowers

• rr = Yellow flowers

• Rr = Orange flowers (intermediate between red and yellow)

❌ Why Other Options Are Incorrect:

b. Polygenic trait controlled by 3 genes

• Polygenic traits show continuous variation (e.g., height, skin color), not discrete categories like red, orange, and yellow.

c. Epistasis

• Epistasis involves one gene masking another, typically altering the expected Mendelian ratios.

d. Maternally inherited trait

• Maternally inherited traits (often mitochondrial) don’t show Mendelian ratios and would not vary like this after self-pollination.

🧠 Key Takeaways

• A 1:2:1 ratio in a self-crossed heterozygous plant is a hallmark of incomplete dominance.

• Orange as a blended phenotype of red and yellow confirms intermediate inheritance.

• Simple Mendelian genetics still beautifully explains complex biological patterns!

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📌 Final Answer: (a) the gene for flower colour shows incomplete dominance.
This explains the 1:2:1 distribution of red, orange, and yellow flowers in the F1 progeny.