All questions of DNA Technology for Grade 9 Exam

For gene transfer into the host cell without using vector microparticles made of tungsten and gold coated with foregin DNA are bombarded into target cells at a very high velocity. This method is called biolistics or gene gun which is suitable for plants.So the correct option is 'gold or tungsten'.

Restriction endonuclease is a type of enzyme that can cleave molecules of DNA at a particular site called restriction site having polindromic sequence. These enzymes are produced by many bacteria and protect the cell by cleaving and destroying the DNA of invading viruses. Now a days, restriction enzymes are widely used in the techniques of genetic engineering.Therefore, the correct answer is option 'A'.

Overview of Restriction Endonucleases
Restriction endonucleases, also known as restriction enzymes, are crucial in molecular biology for manipulating DNA. Let's evaluate the statements provided regarding these enzymes.
Statement Analysis
- i. Hind II was the first restriction endonuclease discovered and cuts DNA at a specific sequence of six base pairs.
- This statement is incorrect. Hind II was not the first restriction enzyme discovered; that title goes to Hind II's predecessor, Hind I. Additionally, while Hind II does cut DNA at a specific site, it does not necessarily cut at a sequence of six base pairs.
- ii. The convention for naming these enzymes is the first 2 letters of the name comes from the genus and the second one letter comes from the species of the prokaryotic cell from which they were isolated.
- This statement is correct. For example, EcoRI is derived from Escherichia coli (genus: Eco, species: R).
- iii. Exonucleases and endonucleases are both types of restriction enzymes that function by cutting DNA at specific sites.
- This statement is incorrect. Exonucleases remove nucleotides from the ends of DNA, while endonucleases cut within the DNA strand. Only endonucleases are classified as restriction enzymes.
- iv. Each restriction endonuclease can only recognize and cut palindromic sequences in the DNA.
- This statement is correct. Most restriction enzymes recognize specific palindromic sequences in the DNA, which are sequences that read the same forwards and backwards.
Correct Statements
Based on the analysis, the correct statements are ii and iv. Thus, the correct answer is option 'c' (i and iv).

Understanding the Assertion and Reason
The assertion and reason provided in the question relate to the use of alternative selectable markers in recombinant DNA technology.
Assertion (A): The use of alternative selectable markers in recombinant DNA technology simplifies the identification of recombinant colonies.
- Selectable markers are crucial in recombinant DNA technology.
- They help distinguish between colonies that contain recombinant DNA and those that do not.
- By using alternative markers, researchers can streamline the identification process.
Reason (R): These markers allow for the differentiation of recombinants from non-recombinants based solely on color change in the presence of a chromogenic substrate.
- Chromogenic substrates react with specific markers to produce a color change.
- This color change serves as a visual indicator of successful recombination.
- It provides a straightforward method for identifying recombinant colonies.
Why Option A is Correct
- Both the assertion and reason are true.
- The assertion accurately reflects that alternative selectable markers simplify the identification process.
- The reason correctly explains how these markers function, specifically highlighting the role of color change in differentiating recombinants from non-recombinants.
Conclusion
- Therefore, option "A" is correct, as both statements are true, and the reason provided is indeed the correct explanation for the assertion.
- This understanding enhances the efficiency of selecting recombinant DNA in laboratory settings, showcasing the importance of these techniques in biotechnology.

Gel electrophoresis is used to separate macromolecules like DNA, RNA and proteins. DNA fragments are separated according to their size. Proteins can be separated according to their size and their charge (different proteins have different charges).

Understanding Selectable Markers in E. coli
Selectable markers are essential tools in molecular biology, particularly for the transformation and selection of genetically modified organisms. In the case of E. coli, certain markers are commonly used, while others may not be effective.
Common Selectable Markers
- Ampicillin Resistance Gene: This gene allows E. coli to survive in the presence of ampicillin, making it a widely used selectable marker for plasmids.
- Chloramphenicol Resistance Gene: Similar to the ampicillin resistance gene, this marker enables E. coli to grow in the presence of chloramphenicol, facilitating the selection of transformed cells.
- Tetracycline Resistance Gene: This gene provides E. coli with resistance to tetracycline, allowing for the selection of successfully transformed bacteria.
Why Penicillin Resistance is NOT a Useful Marker
- Drug Resistance E.coli Gene Against Penicillin: While penicillin resistance may seem like a viable option, it is not considered a useful selectable marker in E. coli for several reasons:
- Ineffectiveness in E. coli: E. coli is inherently resistant to penicillin due to its cell wall structure. Therefore, using a penicillin resistance gene does not provide a selection advantage, as E. coli can grow in penicillin-containing media without any genetic modification.
- Lack of Selection Pressure: Since E. coli can already survive in penicillin, it fails to distinguish transformed from non-transformed cells, rendering it ineffective as a selectable marker.
In conclusion, when selecting markers for E. coli, it is crucial to choose those that provide a clear selection advantage, such as ampicillin, chloramphenicol, or tetracycline resistance genes, while avoiding options like penicillin resistance that do not serve this purpose.