Question:
Given below are two statements:
Statement I: Term heterosis was first used by Shull (1914) and is defined as the superiority of an \(F_1\) hybrid over both its parents in terms of yield and some other characters.
Statement II: Genetic basis of heterosis is explained by two main theories namely dominance hypothesis and over dominance hypothesis.
In light of the above statements, choose the most appropriate answer from the options given below: [Question ID = 582][Question Description = 202_30_HOR_AUG22_Q102]
Given below are two statements:
Statement I: Term heterosis was first used by Shull (1914) and is defined as the superiority of an \(F_1\) hybrid over both its parents in terms of yield and some other characters.
Statement II: Genetic basis of heterosis is explained by two main theories namely dominance hypothesis and over dominance hypothesis.
In light of the above statements, choose the most appropriate answer from the options given below: [Question ID = 582][Question Description = 202_30_HOR_AUG22_Q102]
Statement I: Term heterosis was first used by Shull (1914) and is defined as the superiority of an \(F_1\) hybrid over both its parents in terms of yield and some other characters.
Statement II: Genetic basis of heterosis is explained by two main theories namely dominance hypothesis and over dominance hypothesis.
In light of the above statements, choose the most appropriate answer from the options given below: [Question ID = 582][Question Description = 202_30_HOR_AUG22_Q102]
Show Hint
Heterosis is the basis of the commercial hybrid seed industry. Remember: Shull = Term "Heterosis" (1914); Davenport = Dominance Hypothesis; East and Shull = Overdominance.
Updated On: Aug 7, 2026
- Both Statement I and Statement II are correct [Option ID = 2325]
- Both Statement I and Statement II are incorrect [Option ID = 2326]
- Statement I is correct but Statement II is incorrect [Option ID = 2327]
- Statement I is incorrect but Statement II is correct [Option ID = 2328]
Show Solution
Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Heterosis, or hybrid vigor, is a biological phenomenon where the offspring of diverse parents exhibit enhanced biological qualities such as growth rate, size, fecundity, and yield compared to the parental lines.
Step 2: Detailed Explanation:
Statement I Analysis: The term "heterosis" was indeed coined by G.H. Shull in 1914 to describe the phenomenon previously referred to as hybrid vigor. Shull's work, primarily with maize, demonstrated that crossing inbred lines resulted in offspring that significantly outperformed the parents. Heterosis is generally calculated as the percentage improvement of the \(F_1\) over the mid-parent value (average of both parents) or better-parent value.
Statement II Analysis: Scientists have proposed several theories to explain why heterosis occurs at the genetic level.
1. Dominance Hypothesis: Proposed by Davenport (1908), it suggests that heterosis is due to the masking of deleterious recessive alleles from one parent by dominant favorable alleles from the other parent.
2. Overdominance Hypothesis: Proposed by East and Shull (1908), it suggests that the heterozygous state (\(Aa\)) is inherently superior to either homozygous state (\(AA\) or \(aa\)) at certain loci.
Other theories like the Epistasis hypothesis also exist, but Dominance and Overdominance remain the two classical primary pillars of heterosis theory. Since both statements align with established genetic and historical facts, they are both correct.
Step 3: Final Answer:
Both Statement I and Statement II are correct.
Heterosis, or hybrid vigor, is a biological phenomenon where the offspring of diverse parents exhibit enhanced biological qualities such as growth rate, size, fecundity, and yield compared to the parental lines.
Step 2: Detailed Explanation:
Statement I Analysis: The term "heterosis" was indeed coined by G.H. Shull in 1914 to describe the phenomenon previously referred to as hybrid vigor. Shull's work, primarily with maize, demonstrated that crossing inbred lines resulted in offspring that significantly outperformed the parents. Heterosis is generally calculated as the percentage improvement of the \(F_1\) over the mid-parent value (average of both parents) or better-parent value.
Statement II Analysis: Scientists have proposed several theories to explain why heterosis occurs at the genetic level.
1. Dominance Hypothesis: Proposed by Davenport (1908), it suggests that heterosis is due to the masking of deleterious recessive alleles from one parent by dominant favorable alleles from the other parent.
2. Overdominance Hypothesis: Proposed by East and Shull (1908), it suggests that the heterozygous state (\(Aa\)) is inherently superior to either homozygous state (\(AA\) or \(aa\)) at certain loci.
Other theories like the Epistasis hypothesis also exist, but Dominance and Overdominance remain the two classical primary pillars of heterosis theory. Since both statements align with established genetic and historical facts, they are both correct.
Step 3: Final Answer:
Both Statement I and Statement II are correct.
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