Transgenic animals and plants MCQ Quiz in मल्याळम - Objective Question with Answer for Transgenic animals and plants - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is salinity tolerance

Explanation:

The Arabidopsis AtNHX1 gene encodes a tonoplast Na⁺/H⁺ antiporter which plays a critical role in ion homeostasis, particularly in sodium (Na⁺) sequestration into vacuoles. By compartmentalizing Na⁺ into the vacuole, the antiporter helps to reduce the toxic levels of sodium in the cytoplasm which can be detrimental to plant cells.

• Salinity Tolerance: High soil salinity is a major stress factor that affects plant growth and productivity. The Na⁺/H⁺ antiporter exchanges Na⁺ for H⁺ across the vacuolar membrane (tonoplast), thereby sequestering excess Na⁺ in the vacuoles. This sequestration helps in maintaining cellular ion homeostasis and reducing ion toxicity, which enables the plant to survive and grow better under saline conditions.
• Transgenic Plants: Plants engineered to overexpress the AtNHX1 gene exhibit enhanced ability to tolerate high salinity conditions because they can effectively compartmentalize and neutralize the excessive sodium ions.

Therefore, the correct answer is salinity tolerance.

The correct answer is A, C and D

Explanation:

Agrobacterium tumefaciens is a gram-negative soil bacterium known for its role in plant biotechnology, especially in the genetic engineering of plants.

It causes crown gall disease in dicotyledonous plants by transferring a part of its DNA (T-DNA) into the plant genome, which leads to tumor formation.

• Statement A: A. tumefaciens is indeed a gram-negative soil bacterium. This is a well-established fact about the bacterium, known for its role in causing crown gall disease in plants.
• Statement B: Opine catabolism genes are present in the T-DNA region of the Ti-plasmid (Incorrect): The genes for opine catabolism are not present in the T-DNA region; they are located in the non-T-DNA region of the Ti-plasmid. The T-DNA region contains genes that are transferred to the plant cell, which contribute to tumor formation and opine synthesis.
• Statement C: Opines are synthesized by the condensation of amino acids and keto acids or amino acids and sugars. This process occurs in the transformed plant cells and the opines are then utilized by A. tumefaciens.
• Statement D: The T-DNA transferred to the plant cells contains genes that lead to the autonomous synthesis of phytohormones by the plant cells, allowing crown gall tissues to grow without the addition of external phytohormones.

Thus, the correct combination of statements is A, C, and D.

The correct answer is A, B, and C.

Explanation:

A. Enzyme ‘4’ has greater affinity for D than enzyme ‘3’:

• This statement suggests that enzyme 4 has a greater affinity for the intermediate D than enzyme 3. If enzyme 4 has a higher affinity for D, it may dominate the conversion of D into another product, potentially limiting the amount of substrate available for enzyme 5.

B. Feedback inhibition of enzyme ‘5’ by compound X:

• This statement suggests that compound X might inhibit enzyme 5 through feedback inhibition. Many biochemical pathways exhibit feedback regulation, where the product of the pathway (in this case, X) can inhibit the enzyme responsible for its own production to maintain homeostasis.
• If X is inhibiting enzyme 5, increasing the expression of enzyme 5 might not necessarily lead to an increase in the production of X, as the inhibition could limit the enzyme’s activity even in the transgenic plants. This would explain why a proportionate increase in X was not observed.

C. Substrate limitation for enzyme ‘5’:

• This statement suggests that there might not be enough substrate available for enzyme 5 to act on, even though the enzyme is being over-expressed.
• If there is a substrate limitation, over-expressing enzyme 5 would not result in an increase in the production of X, because there would be insufficient precursor material for the enzyme to process. This would explain why the level of X did not increase proportionally with the increased enzyme levels.

Conclusion: All three factors (A, B, and C) could contribute to the lack of a proportionate increase in X in the transgenic plants.​Thus, the correct answer is A, B, and C.

The correct answer is A and C.

Concept:

• Agrobacterium-mediated transformation is a common method used to introduce foreign genes (transgenes) into plant genomes. This process typically involves a selection marker gene and a passenger gene.
• Transgene expression can vary significantly among independent transgenic plants due to several factors, including position effects, transgene copy number, and other molecular mechanisms.

Explanation:

• Position effects on passenger gene (A): When a transgene is inserted into the plant genome, its expression can be influenced by the genomic location of the insertion site. Certain genomic regions are more conducive to high levels of gene expression, while others may suppress it. This is known as the position effect and is a significant cause of variability in transgene expression levels.
• Variation in copy number of passenger gene (C): The number of copies of the transgene integrated into the plant genome can also affect expression levels. Higher copy numbers can lead to increased expression, but they can also lead to transgene silencing due to mechanisms like homology-dependent gene silencing. Therefore, variation in copy number among transgenic plants can lead to variability in expression levels.

Incorrect Options:

• Transgene silencing of the marker gene (B): While transgene silencing can occur, it typically affects the expression of the transgene itself rather than the marker gene. Moreover, if the marker gene were silenced, it would not directly explain the variability in the expression of the passenger gene "Y".
• mRNA instability of marker gene (D): Instability of the marker gene's mRNA would affect the selection process but not necessarily the expression levels of the passenger gene "Y". The observed variability in "Y" expression is more likely due to factors directly affecting "Y", such as position effects and copy number variation.

The correct answer is mutation in gene “A” induces zygotic lethality

Concept:

• T-DNA mediated insertional mutagenesis is a technique used to disrupt gene function in plants, allowing researchers to identify genes involved in specific biological processes.
• In this method, T-DNA (Transfer DNA) from Agrobacterium tumefaciens is inserted into the plant genome, which can interrupt gene function. The T-DNA often carries a selectable marker, such as a Kanamycin-resistance gene, to identify transformed plants.
• When a mutant plant is self-pollinated, the segregation ratio of the progeny can provide clues about the nature of the mutation and its effects on the plant's development and viability.

Explanation:

• In the given experiment, the T₀ plant has a T-DNA insertion in gene "A". This insertion confers Kanamycin resistance.
• Self-pollination of the T₀ plant produced F1 progeny with a 2:1 ratio of Kanamycin resistance to sensitivity. This indicates that only two-thirds of the progeny are viable and resistant, while one-third are sensitive and non-viable.
• This 2:1 ratio suggests that the mutation in gene "A" leads to lethality when homozygous (i.e., when the progeny inherit the mutant allele from both parents).
• Therefore, the correct answer is that the mutation in gene "A" induces zygotic lethality. The zygote (fertilized egg) carrying two copies of the mutant allele is not viable and does not develop further.

Other Options:

• Option 1: The mutant allele did not segregate from the wild type allele. This is incorrect because the 2:1 segregation ratio indicates that the mutant allele did segregate, but the homozygous mutants are non-viable.
• Option 2: Mutation in gene “A” induces lethality in the male gametophyte. This is incorrect because if the mutation affected male gametophyte viability, we would expect a different segregation ratio, likely impacting the transmission of the mutant allele through pollen.
• Option 3: Mutation in gene “A” induces lethality in the female gametophyte. This is incorrect because if the mutation affected female gametophyte viability, the segregation ratio would also differ, impacting the transmission through ovules.
• Option 4: Mutation in gene “A” induces zygotic lethality. This is correct because the observed 2:1 segregation ratio indicates that zygotes homozygous for the mutant allele are non-viable, leading to their absence in the progeny.

The correct answer is The T₀ plant is a double-copy event and the two transgene copies are tightly linked

Concept:

• Transgenic plants contain inserted genes (transgenes) that provide specific traits, such as herbicide resistance.
• Southern blot analysis is a molecular biology technique used to detect specific DNA sequences within a DNA sample.
• Segregation ratios in progeny can provide information about the number and arrangement of transgene copies in the parent plant.

Explanation:

• Single-Copy Event: If the T₀ plant were a single-copy event, it would show a single band on the Southern blot analysis. However, the T₀ plant shows two bands, indicating the presence of more than one copy of the transgene. Thus, Option 1 is incorrect.
• Double-Copy Event (Tightly Linked): The presence of two bands on the Southern blot suggests that the plant has two copies of the transgene. The segregation ratio of 3:1 for herbicide resistance in the T1 progeny indicates that the two transgene copies are tightly linked and inherited together as a single genetic unit. This explains why the expected Mendelian ratio is observed. Therefore, Option 2 is correct.
• Double-Copy Event (Different Chromosomes): If the two transgene copies were integrated into two different chromosomes, the segregation ratio would not consistently follow a 3:1 pattern, as independent assortment would result in more complex ratios. Thus, Option 3 is incorrect.
• Truncated Versions: The assumption that both transgene copies are truncated versions is not supported by the 3:1 segregation ratio. Truncated versions would likely not confer complete herbicide resistance, and the segregation pattern would be more variable. Therefore, Option 4 is incorrect.

The correct answer is Option 4 i.e. A and D.

Explanation-

• The routine generation of single-copy transgenic events is therefore a major goal for agricultural biotechnology.
• Integration of transfected DNA into the plant genome usually takes place by a process of non-homologous or illegitimate recombination.
• This random integration of transgenes, but also variations in copy number and the configuration of the transgene, which may result in gene silencing, have been implicated to explain differences in gene expression levels between individual transformants. 

A. Difference in restriction enzyme sites within the T-DNA:

• Effect on expression: The presence or absence of specific restriction enzyme sites within the T-DNA may affect the efficiency of cloning and insertion into the vector. However, it may not directly influence the expression level of the transgene once integrated into the plant genome.

B. Difference in copy number of the transgene:

• Effect on expression: Variation in the copy number of the transgene can significantly impact expression levels. Higher copy numbers generally lead to higher expression, while lower copy numbers may result in lower expression.

C. Variations in site of integration of the T-DNA within the plant genome:

• Effect on expression: The site of integration within the plant genome can influence transgene expression. Integration into regions with favorable regulatory elements may enhance expression, while integration into less favorable regions may result in lower expression.

D. Presence of multiple promoters within the T-DNA region:

• Effect on expression: Multiple promoters within the T-DNA can lead to increased expression of the transgene. Each promoter can independently drive the expression of the gene, potentially resulting in higher overall expression.

(A & D) This combination suggests that differences in restriction enzyme sites (A) and the presence of multiple promoters (D) are the only factors considered. While restriction enzyme sites may not directly impact expression, the presence of multiple promoters can influence expression positively.
Conclusion-In summary, option 4) A and D only suggests that the presence of multiple promoters is the primary factor influencing expression levels, while differences in restriction enzyme sites are considered but may not have a direct impact on expression.

The correct answer is A and B

Concept:

• When a prokaryotic gene is expressed in a eukaryotic system, several factors can affect the transcription and processing of the mRNA.
• Alternative splicing and premature transcription termination are common issues that can lead to multiple mRNA transcript lengths.

Explanation:

• Statement A: The three mRNAs (555 bp, 981 bp, and 1257 bp) represent alternatively spliced transcripts due to the presence of putative intronic sequences in the gene.
  • Prokaryotic genes do not typically contain introns, but when cloned into eukaryotic systems, certain sequences may be recognized as splice sites by the eukaryotic splicing machinery.
  • This can lead to the production of multiple mRNA variants of different lengths, as observed in transgenic tobacco plants.
• Statement B: The gene sequence was characterized by the presence of potential polyadenylation signals that resulted in premature termination of transcription.
  • Polyadenylation signals in the gene sequence can cause the transcription machinery to terminate prematurely, resulting in shorter mRNA transcripts.
  • This explains the presence of the 555 bp and 981 bp mRNAs in addition to the full-length 1257 bp transcript.

Incorrect Options:

• Statement C: Expression of full-length transcripts (1257 bases) was lethal to the transformed cells.
  • This statement is incorrect because the presence of the 1257 bp mRNA indicates that full-length transcripts are being produced and not necessarily lethal.
• Statement D: The transgenic plants were chimeric in nature and comprised of a mix of transformed and untransformed cells.
  • Chimerism would not explain the presence of three distinct mRNA lengths derived from the transgene within the same cells.
  • Chimeric plants would result in different cells expressing different genes, not different transcript lengths from the same gene.

Key Points

​Molecular breeding:

• ​ (MB) may be defined in a broad-sense as the use of genetic manipulation performed at DNA molecular levels to improve characters of interest in plants and animals, including genetic engineering or gene manipulation, molecular marker-assisted selection, genomic selection, etc.
• More often, however, molecular breeding implies molecular marker-assisted breeding (MAB) and is defined as the application of molecular biotechnologies, specifically molecular markers, in combination with linkage maps and genomics, to alter and improve plant or animal traits on the basis of genotypic assays.
• This term is used to describe several modern breeding strategies, including marker-assisted selection (MAS), marker-assisted backcrossing (MABC), marker-assisted recurrent selection (MARS), and genome-wide selection (GWS) or genomic selection (GS).

 Genetic markers in plant breeding:

• Genetic markers are the biological features that are determined by allelic forms of genes or genetic loci and can be transmitted from one generation to another, and thus they can be used as experimental probes or tags to keep track of an individual, a tissue, a cell, a nucleus, a chromosome or a gene.
• Genetic markers used in genetics and plant breeding can be classified into two categories:
• Classical markers and
• DNA markers
• Classical markers include morphological markers, cytological markers and biochemical markers.
• DNA markers have developed into many systems based on different polymorphism-detecting techniques or methods (southern blotting – nuclear acid hybridization, PCR – polymerase chain reaction, and DNA sequencing)  such as RFLP, AFLP, RAPD, SSR, SNP, etc.​

Explanation:

• A molecular marker is defined as any DNA sequence which shows polymorphism and can be detected using a molecular technique.
• Molecular markers allow detection of variations or polymorphisms that exist among individuals in the population for specific regions of DNA (e.g. RFLP, AFLP, SNP, etc.).

Hence the correct answer is option 1

Key Points

Genetic breeding strategies 

• Genetic breeding strategies in transgenic organisms are an essential part of molecular biology and biotechnology.
• They involve introducing a foreign gene, or transgene, into a host organism's genome via genetic engineering.
• These transgene sequences can originate from the same species or different species, and they bring about some desirable characteristics that can be passed onto subsequent generations.
• Transgenic animals, including mice, are typically generated by incorporating the transgene into the genomes of germ cells (sperm or egg) or early-stage embryos.
• The resulting animals are then bred to study the function and characteristics of the transgene.
• When breeding transgenic animals, a common strategy is to use heterozygous animals, those with just one copy of the transgene.
• These animals are usually fertile and can pass the transgene onto half of their offspring on average.
• This strategy provides a steady supply of transgenic animals for research and conserves the resources involved in generating new transgenic individuals.
• However, problems can arise if inbreeding (breeding between closely related animals) occurs over numerous generations, such as infertility or the onset of undesirable traits.
• To prevent these issues, a recommended practice is to breed the transgenic animals with wild-type (those without the transgene) animals, especially during the initial generations.
• This practice not only ensures that a consistent population of transgenic animals is maintained but also keeps the population genetically diverse, thus counteracting the issues associated with long-term inbreeding.
• This strategy is typically practical, economical, and greatly assists in achieving the scientific objectives of creating the transgenic animals in the first place.
• Overall, genetic breeding strategies in transgenic organisms require careful planning and understanding of the genetics of the particular species and the introduced transgene, with an emphasis on preventing inbreeding and ensuring the health and continued availability of transgenic animals for scientific research.

Explanation:

• The most preferable and economical approach to continually obtain heterozygous transgenic animals would be option (2), crossing (breeding) of transgenic mice with wild type mice in earlier generations for continued production of transgenic heterozygous offspring.
• This option serves two purposes.
• Firstly, it helps maintain the genetic variability within the population and reduces the risk of promoting detrimental recessive traits through inbreeding. Secondly, it maintains a steady supply of heterozygous transgenic organisms that can be used for future breeding or study.

Hence the correct answer is option 2