Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R).
• [Assertion (A):] In nature, the tetraploid and hexaploid wheat reproduce as diploid (\(2n=28\) or \(2n = 42\)).
• [Reason (R):] In the presence of the Ph1 allele in chromosome 5B, each chromosome pairs only with its homologue from the same genome and reproduces as diploid.
In light of the above statements, choose the correct answer from the options given below.
Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R).
• [Assertion (A):] In nature, the tetraploid and hexaploid wheat reproduce as diploid (\(2n=28\) or \(2n = 42\)).
• [Reason (R):] In the presence of the Ph1 allele in chromosome 5B, each chromosome pairs only with its homologue from the same genome and reproduces as diploid.
In light of the above statements, choose the correct answer from the options given below.
Show Hint
Its function allows allopolyploid wheat to maintain stable, diploid-like inheritance over generations.
- Both (A) and (R) are true and (R) is the correct explanation of (A).
- Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
- (A) is true but (R) is false.
- (A) is false but (R) is true.
The Correct Option is A
Solution and Explanation
Allopolyploid species, such as cultivated tetraploid wheat (Triticum turgidum, genome AABB) and hexaploid wheat (Triticum aestivum, genome AABBDD), contain multiple homeologous (similar but not identical) chromosome sets.
Despite having multiple chromosome sets, these species behave functionally as diploids during meiosis, forming only bivalents instead of multi-chromosome complexes (multivalents).
Step 3: Detailed Explanation:
Let us analyze the Assertion and Reason statements:
- Assertion (A) is true: During meiosis in polyploid wheat, chromosomes pair strictly with their exact homologous partners.
This prevents pairing between homeologous chromosomes from different genomes (e.g., pairing between an A-genome chromosome and a B-genome chromosome).
As a result, only bivalents are formed, and the plant behaves as a functional diploid, producing stable gametes with \(n=14\) (tetraploid) or \(n=21\) (hexaploid) chromosomes.
- Reason (R) is true: This diploid-like chromosome pairing behavior is controlled by a dominant gene locus called {Ph1 (Pairing Homoeologous 1), located on the long arm of chromosome 5B.
The Ph1 gene suppresses homoeologous chromosome pairing, ensuring that chromosomes only pair with their exact homologs from the same genome.
If the Ph1 gene is mutated or absent, homeologous pairing occurs, leading to multivalent formation, meiotic instability, and sterility.
Because the presence of the Ph1 allele is the specific genetic mechanism that allows polyploid wheat to behave as a functional diploid during reproduction, the Reason is the correct explanation of the Assertion.
Step 4: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A), matching Option (A).
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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.
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• [(A).] Fertilizer requirement.
• [(B).] Vernalization requirement.
• [(C).] Winter hardiness (cold tolerance)
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• [(B).] Hybrid crops need intensive care and more inputs.
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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:
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