(a) (i) Name the segment of DNA shown in the diagram - HSC - SSCE Biology - Question 33 - 2014 - Paper 1

DNA has a remarkable ability to repair itself through several mechanisms.

1. Nucleotide Excision Repair (NER): This mechanism removes damaged sections of DNA, typically those caused by environmental factors like UV light. The cell identifies the damaged area, excises it, and fills in the gap with the appropriate nucleotides.

2. Base Excision Repair (BER): This process is utilized when DNA has minor alterations, such as single base modifications. Specific enzymes recognize damaged bases, remove them, and replace them with the correct ones.

3. Homologous Recombination: In double-strand breaks, this mechanism uses an undamaged homologous DNA strand as a template to accurately repair the break, ensuring no loss of genetic information.

Here's a simplified flow chart representing the process of gene cloning using the example of insulin production:

1. **Isolate Gene of Interest**
   - Determine the human insulin gene sequence.

2. **Insert Gene into Plasmid**
   - Use restriction enzymes to cut plasmid DNA.
   - Combine human insulin gene with plasmid DNA using DNA ligase.

3. **Transform Bacterial Cells**
   - Introduce recombinant plasmid into bacterial cells such as E. coli.

4. **Culture Bacteria**
   - Grow bacteria in a suitable medium to allow for replication.

5. **Harvest Insulin**
   - Extract and purify the insulin produced by the bacteria.

This flow chart outlines the key steps involved in cloning the insulin gene and its expression in bacteria.

Blood groups and highly variable genes play a critical role in paternity testing, though they have different strengths and limitations.

1. Blood Group Testing: Blood type can provide initial information about paternity. However, it is limited since multiple individuals can share the same blood type, leading to inconclusive results.

2. Highly Variable Genes (e.g., STRs and SNPs): These genetic markers are more informative as they show greater variability among individuals. For instance, Short Tandem Repeats (STRs) can provide a profile with multiple alleles, allowing for a comparison between the child and potential parents.

3. Advantages of Highly Variable Genes:

   • STR analysis is highly accurate and can discriminate between individuals, making it more useful in confirming biological relationships compared to blood types.
   • They provide a probabilistic approach to paternity tests, where the likelihood of a relationship can be quantified.

4. Limitations:

   • Blood groups are not as definitive as DNA profiling, so relying solely on them can lead to errors in paternity assessments. Conversely, testing for highly variable genes requires contemporary methods and technology, making it more costly.

In summary, while blood group tests can indicate compatibility, highly variable genes offer a more precise and reliable method for determining paternity.