The objections to the 'Dominance Hypothesis' of heterosis and inbreeding depression are-
(A). Mostly, it is not possible to isolate inbreds as vigorous as hybrids
(B). Asymmetrical distribution of quantitative traits in the F2 population
(C). Magnitude of heterosis in inbred lines has increased over time, which was not expected as per the hypothesis
(D). Faster inbreeding depression in tetraploids
Choose the correct answer from the options given below:
(A). Mostly, it is not possible to isolate inbreds as vigorous as hybrids
(B). Asymmetrical distribution of quantitative traits in the F2 population
(C). Magnitude of heterosis in inbred lines has increased over time, which was not expected as per the hypothesis
(D). Faster inbreeding depression in tetraploids
Choose the correct answer from the options given below:
Show Hint
- Failure to isolate inbreds as vigorous as the \(F_1\) hybrid.
- Symmetrical (not asymmetrical) distribution of quantitative traits in the \(F_2\) generation.
- (A), (B) and (C) only.
- (A), (B) and (D) only.
- (A), (C) and (D) only.
- (B), (C) and (D) only.
The Correct Option is A
Solution and Explanation
Heterosis (hybrid vigor) describes the increased performance of an \(F_1\) hybrid compared to its inbred parents.
The dominance hypothesis suggests that heterosis is caused by the masking of deleterious recessive alleles from one parent by dominant alleles from the other parent.
Step 2: Detailed Explanation:
While the dominance hypothesis is a major model for heterosis, early geneticists raised several objections to it:
(A) is a valid objection because if heterosis is due to dominant alleles, it should be theoretically possible to isolate homozygous dominant lines (e.g., \(AABBCC\)) that are as vigorous as the heterozygous \(F_1\) hybrid.
In practice, breeders have not been able to isolate inbred lines with vigor equal to the hybrid.
(B) is a valid objection because segregating dominant and recessive alleles in the \(F_2\) generation should produce an asymmetrical (skewed) distribution of quantitative traits based on the 3:1 ratio.
In practice, \(F_2\) populations typically display a symmetrical, normal bell curve distribution.
(C) is a valid objection because the gradual accumulation of dominant alleles in inbred lines over generations of selection was expected to decrease the relative magnitude of heterosis when crossed, which is inconsistent with observed breeding results.
(D) is incorrect because tetraploid plants show a slower rate of inbreeding depression than diploid plants.
This is due to their complex chromosome segregation, which requires more generations of selfing to reach complete homozygosity.
Therefore, (A), (B), and (C) are the correct objections to the dominance hypothesis.
Step 3: Final Answer:
The correct combination is (A), (B), and (C) only, corresponding to option (A).
Top ICAR AIEEA Plant Sciences Questions
- Both plant and animal cells contain some small organelles called 'peroxisomes', which are dedicated to the metabolism of substances such as
- Chemicals that store energy for the majority of work within cells are called
- The longest phase during the eukaryotic cell cycle is
- The formula: [Sum of (Observed-Expected)$^2$/Expected] is also known as
- Human beings have a large-sized 'proteome'. The principal and more significant reason for this is-
Top ICAR AIEEA Genetics & Plant Breeding Questions
Select the correct statements about origin of the tetraploid and hexaploid wheat:
• [A.] The tetraploid species Triticum turgidum is an allopolyploid.
• [B.] The hexaploid species Triticum aestivum is an allopolyploid.
• [C.] Triticum turgidum arose from a combination of Triticum monococcum and Triticum timopheevii genomes.
• [D.] Triticum aestivum arose from a combination of Triticum turgidum and Aegilops tauschii genomes.The physiological characteristics of wheat plants that adapt different wheat cultivars to different climates include-
• [(A).] Fertilizer requirement.
• [(B).] Vernalization requirement.
• [(C).] Winter hardiness (cold tolerance)
• [(D).] Photoperiod response. Choose the correct answer from the options given below:
Male sterile cytoplasm in crop plants usually arises from-
• [(A).] Inter-specific hybridization
• [(B).] Self-incompatibility
• [(C).] Spontaneous mutation
• [(D).] Induced mutation through Ethium Bromide Choose the correct answer from the options given below:
Which of the following statements is NOT correct?
• [(A).] Seeds of synthetic varieties need to be replaced every year.
• [(B).] Hybrid crops need intensive care and more inputs.
• [(C).] Open pollinated progeny test is used in Maize and Pearl millet.
• [(D).] Composite varieties exploit both GCA and SCA. Choose the correct answer from the options given below:
Which of the following combinations of the premises of 'Gamete Selection' in plant breeding is the correct one?
• [(A).] Multiparent crosses are required for simultaneous improvements of multiple traits.
• [(B).] The male parents of the final crosses are heterozygous and hence heterogametic.
• [(C).] Each zygotic seed is a product of a separate, independent fertilization event.
• [(D).] Gametic selection is an effective method to isolate an inbred for hybrid breeding.
Choose the correct answer from the options given below:
Top ICAR AIEEA Questions
- Which of the following statements is false?
- Which of the following is an example of an inventory?
- According to Adam Smith, productivity gains could be brought about through .
- The supply curve for an artificially scarce good is .
- Which of the following would not be considered an opportunity cost of paid employment?