Following statements were given regarding factors influencing variation in expression levels of transgene in transgenic plants: A. Difference in restriction enzyme sites within the T-DNA. B. Difference in copy number of the transgene. C. Variations in site of integration of the T-DNA within the plant genome. D. Presence of multiple promoters within the T-DNA region. Which one of the following options represents a combination of statements that would NOT lead to variations in transgene expression levels in transgenic plants generated using the same T-DNA/binary vector?
A and D only
Transgene Expression Variation Factors
When creating transgenic plants using the same T-DNA/binary vector construct, scientists often observe differences in how much the introduced gene (transgene) is expressed in different individual plants. This variation in expression levels is influenced by several factors related to how the transgene integrates into the plant's genome and its subsequent behavior.
Analyzing Factors Influencing Transgene Expression
Let's look at the given statements regarding factors that might influence variations in transgene expression levels in transgenic plants:
- Statement A: Difference in restriction enzyme sites within the T-DNA.
- Statement B: Difference in copy number of the transgene.
- Statement C: Variations in site of integration of the T-DNA within the plant genome.
- Statement D: Presence of multiple promoters within the T-DNA region.
The question asks which combination of these factors would NOT lead to variations in expression levels among different transgenic plants generated using the same T-DNA/binary vector construct. This means we are looking for factors that are constant or irrelevant for causing differences *between* individual transgenic lines derived from the same transformation process.
Evaluating Each Statement:
- Statement A: Difference in restriction enzyme sites within the T-DNA. If the same T-DNA/binary vector is used for all transformations, the sequence of the T-DNA, including any restriction enzyme sites within it, is identical in the construct. Any potential differences in restriction sites would only be relevant during the construction of the vector, not in causing variation in expression levels after the stable integration of the T-DNA (derived from the same vector) into different plants. Therefore, differences in restriction enzyme sites within the T-DNA (of the same construct) would NOT cause variation in transgene expression levels among different transgenic lines.
- Statement B: Difference in copy number of the transgene. The number of copies of the T-DNA that integrate into the plant genome can vary significantly from one transgenic event (plant) to another. A higher copy number can sometimes lead to increased expression, but it can also trigger gene silencing mechanisms, leading to reduced or no expression. This variation in copy number is a well-known cause of variation in transgene expression. Thus, this WOULD lead to variation.
- Statement C: Variations in site of integration of the T-DNA within the plant genome. The location where the T-DNA integrates into the host genome has a major impact on transgene expression. Integration into transcriptionally active chromatin regions is generally associated with higher expression, while integration into heterochromatic or silenced regions can lead to very low or no expression (known as position effect). Since the integration site is essentially random for each transformation event, variations in integration site are a primary cause of expression variation. Thus, this WOULD lead to variation.
- Statement D: Presence of multiple promoters within the T-DNA region. The presence of multiple promoters is a feature of the T-DNA construct itself. If the same T-DNA/binary vector is used for all transformations, then all integrated T-DNA copies will have the same set of promoters within them (unless truncated or rearranged, which is related to integration site effects). While the type and number of promoters *within the construct* determine the potential expression level, the *presence* of these promoters is constant across all transgenic lines generated with that specific construct. It doesn't cause variation *between* lines in the same way that copy number or integration site does. Therefore, the presence of multiple promoters (within the same construct) would NOT cause variation in transgene expression levels among different transgenic lines.
Based on this analysis, statements A and D describe factors that would NOT lead to variations in transgene expression levels among different transgenic plants generated using the same T-DNA/binary vector.
| Statement | Would lead to variation in expression among plants? | Reason |
|---|---|---|
| A. Difference in restriction enzyme sites within the T-DNA | No | Same construct means same restriction sites within the T-DNA. |
| B. Difference in copy number of the transgene | Yes | Varies per integration event; affects expression & silencing. |
| C. Variations in site of integration of the T-DNA | Yes | Integration site (position effect) significantly impacts expression. |
| D. Presence of multiple promoters within the T-DNA region | No | Feature of the construct; constant across lines from the same construct. |
The factors that would NOT lead to variations in transgene expression levels are A and D.
Important Questions from Transgenic animals and plants
An experiment was performed to introduce a transgenic trait in a crop plant by Agrobacterium-mediated transformation using a transgene construct in which the transgene was expressed using the CaMV 35S promoter. It was observed that expression levels of the transgenic protein were very low in all transgenic plants while transgene mRNA levels were high and variable among different plants. Further, different transgenic lines contained different numbers of the T-DNA insert. The following statements were made to explain the above observation:
A. Variations in the number of T-DNA inserts in different transgenic plants is due to more number of host cells getting infected with the T-DNA
B. Low expression levels of the transgenic protein in all transgenic plants could be due to codon usage variations between the host plant and the heterologous source of the transgene
C. The coding sequence of the transgene contained sequences that destabilized the transgene mRNA
D. Variation in copy number of T-DNA in different transgenic plants is due to variation in the promoter used to express the transgene.
Which one of the following options represents all correct
statements?Which one of the following statements related to genetic transformation of plants is correct?
The following statements are made regarding developing a transgenic mouse:
A. The transgenic mouse thus born will be a homozygous transgenic animal and can be maintained by crossing with another transgenic animal.
B. The fertilized transgenic eggs are allowed to develop in vitro.
C. The desired gene is preferably microinjected in male pronucleus after sperm entry in oocyte.
D. For best efficiency, the desired gene is always microinjected in the male gametes and then they are allowed to fertilize the female gametes.
E. Blastocyst stage embryos are transferred to the uterus of hormonally prepared mother.
F. The fertilized eggs are collected from specific strain of mouse.
G. The female mouse of specific strain is superovulated, oocytes are collected and allowed to fertilize in vitro.
Choose the combination of statements arranged in the correct sequence for developing transgenic mouse.
Which one of the following genomes is most appropriate to determine hybrids in plants and animals?
Given below are a few statements about plant breeding and transgenesis:
A. Recombinant inbred lines and double haploid populations have high levels of genetic homozygosity.
B. Gene pyramiding involves introducing different genes for resistance to a specific pest in different genotypes of a plant species.
C. Agrobacterium strains with a disarmed Ti plasmid do not require vir genes for transfer of T‐DNA.
D. Molecular breeding can be used for crop improvement if the trait of interest is present in naturally occurring populations of the plant.
Which one of the following options represents a combination of INCORRECT statements?
