is a second mutation that compensates for the effect of an...

Filter: 2024 Paper (3 Qs)

Q.1

ICAR AIEEA PG 2024 - Plant Sciences (Q.12)

MCQ (Single Correct) +4 −1

________ is a second mutation that compensates for the effect of an original, first mutation.

Choose the most appropriate option from the below-mentioned options to fill in the gap:

________ एक दूसरा उत्परिवर्तन (second mutation) है जो मूल, पहले उत्परिवर्तन के प्रभाव की भरपाई (compensate) करता है। रिक्त स्थान की पूर्ति के लिए

नीचे दिए गए विकल्पों में से सर्वाधिक उपयुक्त विकल्प चुनिए:

Forward mutation अग्रगामी उत्परिवर्तन Supplementary mutation पूरक उत्परिवर्तन Suppressor mutation दमनकारी उत्परिवर्तन Compensatory mutation प्रतिपूरक उत्परिवर्तन

Suppressor Mutation:

Suppressor mutation is a secondary genetic alteration that suppresses or alleviates the phenotypic consequences of an earlier (first) mutation, restoring the wild-type or near wild-type phenotype without reversing the original mutation.
Suppressors are categorized into:

Intragenic suppressors: Occur within the same gene as the first mutation (e.g., a compensatory insertion near an earlier deletion that restores reading frame).
Intergenic (extragenic) suppressors: Occur in a different gene (e.g., a mutant tRNA gene whose anticodon recognizes a nonsense stop codon introduced by the primary mutation).
- Forward mutation: Mutation from wild type to mutant form.
Reverse/back mutation: Direct reversion of the mutant allele back to the wild-type sequence.

Correct Answer: Option 3 (Suppressor mutation).

विस्तृत व्याख्या:

Suppressor Mutation (सप्रेसर/दमनकारी उत्परिवर्तन):

Suppressor mutation is a secondary genetic alteration that suppresses or alleviates the phenotypic consequences of an earlier (first) mutation, restoring the wild-type or near wild-type phenotype without reversing the original mutation.
Suppressors are categorized into:

Intragenic suppressors: Occur within the same gene as the first mutation (e.g., a compensatory insertion near an earlier deletion that restores reading frame).
Intergenic (extragenic) suppressors: Occur in a different gene (e.g., a mutant tRNA gene whose anticodon recognizes a nonsense stop codon introduced by the primary mutation).
- Forward mutation: Mutation from wild type to mutant form.
Reverse/back mutation: Direct reversion of the mutant allele back to the wild-type sequence.

Correct Answer: Option 3 (Suppressor mutation).

Explanation not matching this question? क्या व्याख्या इस प्रश्न से मेल नहीं खा रही? Report

Q.2

ICAR AIEEA PG 2024 - Plant Sciences (Q.17)

MCQ (Single Correct) +4 −1

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.

Choose the correct answer from the options given below:

चतुर्गुणित (tetraploid) और षट्गुणित (hexaploid) गेहूँ की उत्पत्ति के बारे में सही कथनों का चयन कीजिए:

(A) चतुर्गुणित प्रजाति Triticum turgidum एक एलोपॉलीप्लॉयड (allopolyploid) है।

(B) षट्गुणित प्रजाति Triticum aestivum एक एलोपॉलीप्लॉयड है।

(C) Triticum turgidum की उत्पत्ति Triticum monococcum और Triticum timopheevii जीनोम के संयोजन से हुई।

(D) Triticum aestivum की उत्पत्ति Triticum turgidum और Aegilops tauschii जीनोम के संयोजन से हुई।

नीचे दिए गए विकल्पों में से सही उत्तर चुनिए:

(A), (B) and (C) only केवल (A), (B) और (C) (A), (B) and (D) only केवल (A), (B) और (D) (A), (C) and (D) only केवल (A), (C) और (D) (B), (C) and (D) only केवल (B), (C) और (D)

Evolution of Wheat:

Statement (A) is CORRECT: Tetraploid wheat (Triticum turgidum ssp. durum, $2n = 4x = 28$, genome AABB) is an allopolyploid formed by natural hybridization between T. urartu (AA donor) and an ancestor related to Aegilops speltoides (BB donor).
Statement (B) is CORRECT: Bread wheat (Triticum aestivum, $2n = 6x = 42$, genome AABBDD) is an allohexaploid.
Statement (C) is INCORRECT: T. turgidum (AABB) did NOT arise from T. timopheevii (AAGG); they are distinct tetraploid lineages.
Statement (D) is CORRECT: Hexaploid bread wheat (T. aestivum, AABBDD) arose from spontaneous hybridization between cultivated tetraploid wheat (T. turgidum, AABB) and the wild goat grass Aegilops tauschii (Ae. squarrosa, DD donor), followed by spontaneous chromosome doubling.

Thus, statements (A), (B), and (D) are correct. Correct Answer: Option 2 ((A), (B) and (D) only).

विस्तृत व्याख्या:

Evolution of Wheat (गेहूँ की उत्पत्ति एवं उद्विकास):

Statement (A) is CORRECT: Tetraploid wheat (Triticum turgidum ssp. durum, $2n = 4x = 28$, genome AABB) is an allopolyploid formed by natural hybridization between T. urartu (AA donor) and an ancestor related to Aegilops speltoides (BB donor).
Statement (B) is CORRECT: Bread wheat (Triticum aestivum, $2n = 6x = 42$, genome AABBDD) is an allohexaploid.
Statement (C) is INCORRECT: T. turgidum (AABB) did NOT arise from T. timopheevii (AAGG); they are distinct tetraploid lineages.
Statement (D) is CORRECT: Hexaploid bread wheat (T. aestivum, AABBDD) arose from spontaneous hybridization between cultivated tetraploid wheat (T. turgidum, AABB) and the wild goat grass Aegilops tauschii (Ae. squarrosa, DD donor), followed by spontaneous chromosome doubling.

Thus, statements (A), (B), and (D) are correct. Correct Answer: Option 2 ((A), (B) and (D) only).

Explanation not matching this question? क्या व्याख्या इस प्रश्न से मेल नहीं खा रही? Report

Q.3

ICAR AIEEA PG 2024 - Plant Sciences (Q.37)

Assertion & Reason +4 −1

Given below are two statements, one is labelled as Assertion (A) and other one 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:

नीचे दो कथन दिए गए हैं, एक को अभिकथन (A) और दूसरे को कारण (R) के रूप में लेबल किया गया है:

अभिकथन (A) : प्रकृति में, चतुर्गुणित (tetraploid) और षट्गुणित (hexaploid) गेहूँ द्विगुणित ($2n=28$ या $2n = 42$) के रूप में प्रजनन करते हैं।

कारण (R) : गुणसूत्र 5B में Ph1 एलील की उपस्थिति में, प्रत्येक गुणसूत्र केवल उसी जीनोम के अपने समजात (homologue) के साथ युग्मित होता है और द्विगुणित के रूप में प्रजनन करता है।

उपरोक्त कथनों के आलोक में, नीचे दिए गए विकल्पों में से सही उत्तर चुनिए:

Both (A) and (R) are true and (R) is the correct explanation of (A) (A) और (R) दोनों सत्य हैं और (R), (A) की सही व्याख्या है Both (A) and (R) are true but (R) is NOT the correct explanation of (A) (A) और (R) दोनों सत्य हैं लेकिन (R), (A) की सही व्याख्या नहीं है (A) is true but (R) is false (A) सत्य है लेकिन (R) असत्य है (A) is false but (R) is true (A) असत्य है लेकिन (R) सत्य है

Genetic Control of Diploid-like Pairing in Polyploid Wheat:

Assertion (A) is TRUE: Bread wheat (Triticum aestivum, $2n = 6x = 42$, AABBDD) and durum wheat (Triticum durum, $2n = 4x = 28$, AABB) are allopolyploids containing closely related, homoeologous subgenomes. Despite having multiple related genomes, they strictly form bivalents (21 bivalents in hexaploid, 14 bivalents in tetraploid) during meiotic metaphase I and behave cytogenetically as functional diploids with regular disomic inheritance.
Reason (R) is TRUE and correctly explains (A): This regular bivalent pairing is strictly regulated by the $Ph1$ (Pairing homoeologous 1) locus located on the long arm of chromosome 5B (discovered by Ralph Riley and Ernest Sears). The dominant $Ph1$ gene suppresses pairing between homoeologous (related) chromosomes, restricting synapsis strictly to true homologous pairs within the same genome. When $Ph1$ is deleted or mutated, homoeologous pairing and multivalent formation occur.

Therefore, both (A) and (R) are true and (R) is the correct explanation of (A). Correct Answer: Option 1.

विस्तृत व्याख्या:

Genetic Control of Diploid-like Pairing in Polyploid Wheat (गेहूँ में द्विगुणित युग्मन का आनुवंशिक नियंत्रण):

Assertion (A) is TRUE: Bread wheat (Triticum aestivum, $2n = 6x = 42$, AABBDD) and durum wheat (Triticum durum, $2n = 4x = 28$, AABB) are allopolyploids containing closely related, homoeologous subgenomes. Despite having multiple related genomes, they strictly form bivalents (21 bivalents in hexaploid, 14 bivalents in tetraploid) during meiotic metaphase I and behave cytogenetically as functional diploids with regular disomic inheritance.
Reason (R) is TRUE and correctly explains (A): This regular bivalent pairing is strictly regulated by the $Ph1$ (Pairing homoeologous 1) locus located on the long arm of chromosome 5B (discovered by Ralph Riley and Ernest Sears). The dominant $Ph1$ gene suppresses pairing between homoeologous (related) chromosomes, restricting synapsis strictly to true homologous pairs within the same genome. When $Ph1$ is deleted or mutated, homoeologous pairing and multivalent formation occur.

Therefore, both (A) and (R) are true and (R) is the correct explanation of (A). Correct Answer: Option 1.

Explanation not matching this question? क्या व्याख्या इस प्रश्न से मेल नहीं खा रही? Report