Question:
In a typical monohybrid, a cross with respect to a certain trait, 120 plants are obtained in the \(F_{2}\) generation. What will be the approximate number of homozygous and heterozygous plants respectively?
In a typical monohybrid, a cross with respect to a certain trait, 120 plants are obtained in the \(F_{2}\) generation. What will be the approximate number of homozygous and heterozygous plants respectively?
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The F2 genotypic ratio of a monohybrid cross is 1:2:1. Half of the progeny are heterozygous and half are homozygous.
Updated On: Nov 12, 2026
- 40 and 80.
- 60 and 60.
- 20 and 100.
- 10 and 110.
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept
A monohybrid cross gives the genotypic ratio \(1\ AA : 2\ Aa : 1\ aa\) in the \(F_{2}\) generation.
Homozygous plants are \(AA\) and \(aa\). Heterozygous plants are \(Aa\).
Step 2: Calculation
Total parts in the ratio \(= 1 + 2 + 1 = 4\).
Homozygous fraction \(= \dfrac{2}{4} = \dfrac{1}{2}\), so \(\dfrac{1}{2} \times 120 = 60\).
Heterozygous fraction \(= \dfrac{2}{4} = \dfrac{1}{2}\), so \(\dfrac{1}{2} \times 120 = 60\).
Step 3: Compare the options
Only the option giving equal numbers of homozygous and heterozygous plants, 60 and 60, matches the 1:2:1 ratio.
Final Answer:
About 60 plants are homozygous and 60 plants are heterozygous. \[ \boxed{\text{(B) }\text{60 and 60}} \]
A monohybrid cross gives the genotypic ratio \(1\ AA : 2\ Aa : 1\ aa\) in the \(F_{2}\) generation.
Homozygous plants are \(AA\) and \(aa\). Heterozygous plants are \(Aa\).
Step 2: Calculation
Total parts in the ratio \(= 1 + 2 + 1 = 4\).
Homozygous fraction \(= \dfrac{2}{4} = \dfrac{1}{2}\), so \(\dfrac{1}{2} \times 120 = 60\).
Heterozygous fraction \(= \dfrac{2}{4} = \dfrac{1}{2}\), so \(\dfrac{1}{2} \times 120 = 60\).
Step 3: Compare the options
Only the option giving equal numbers of homozygous and heterozygous plants, 60 and 60, matches the 1:2:1 ratio.
Final Answer:
About 60 plants are homozygous and 60 plants are heterozygous. \[ \boxed{\text{(B) }\text{60 and 60}} \]
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