a) (i) Name the nitrogen base unique to mRNA - HSC - SSCE Biology - Question 32 - 2004 - Paper 1

The information contained in DNA is used to produce a polypeptide through a process called protein synthesis, which involves two main stages: transcription and translation.

1. Transcription: In this stage, the DNA sequence of a gene is transcribed into messenger RNA (mRNA) in the nucleus. RNA polymerase binds to the DNA at the promoter region, unwinding the DNA strands and synthesizing the mRNA strand by adding complementary RNA nucleotides (A-U, C-G).

2. Translation: Once the mRNA is formed, it exits the nucleus and enters the cytoplasm, where ribosomes read the sequence of codons in the mRNA. Transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome. Each tRNA has an anticodon that corresponds to a specific codon on the mRNA. The ribosome facilitates the binding of tRNA to mRNA and catalyzes the formation of peptide bonds between amino acids, resulting in a growing polypeptide chain.

This process continues until a stop codon is reached, at which point the polypeptide is released and folds into its functional form.

1. Define the Objective: State the purpose of modelling linkage; for example, to investigate how genes located on the same chromosome are inherited together.

2. Select the Subjects: Choose organisms for the experiment that exhibit the traits of interest. This could involve selecting parental organisms that possess contrasting traits.

3. Cross the Organisms: Perform a controlled genetic cross by mating the selected organisms, ensuring to keep track of the parental genotypes.

4. Collect Data: Grow the offspring and observe the traits expressed in this generation. Record data on the phenotypes and genotypes of the offspring.

5. Analyze Results: Use the observed ratios of traits in the offspring to determine if the traits follow independent assortment or show linkage, possibly calculating recombination frequencies to quantify linkage.

6. Conclude: Summarize findings in relation to genetic linkage, further discussing the implications for inheritance patterns.

This investigation deepened my understanding of linkage by demonstrating how genes located close together on the same chromosome tend to be inherited together, contrary to the expected Mendelian ratios of independent assortment.

Through practical experience of crossing organisms and analyzing offspring traits, I observed that certain traits did not assort independently. This led me to understand the concept of genetic linkage more clearly, including implications for inheritance patterns, gene mapping, and the significance of recombination in enhancing genetic diversity.

Human intervention in genetics has led to significant changes in society, particularly through agricultural practices, medical advances, and ethical considerations.

1. Agricultural Impact: Genetic modification has allowed for the development of crops that are resistant to pests, diseases, and environmental conditions. This has led to increased food production and security. However, concerns about biodiversity loss and the impact on smallholder farmers must be addressed.

2. Medical Advances: Genetic interventions have led to breakthroughs in medicine, including gene therapy and personalized medicine, allowing for targeted treatments tailored to individual genetic profiles. These innovations have the potential to eradicate genetic disorders and improve overall health outcomes.

3. Ethical Considerations: As we manipulate genetic material, ethical questions arise regarding the implications of 'designer babies', germline editing, and the potential for unintended consequences in the gene pool. Society must engage in discussions to balance innovation with ethical considerations to prevent adverse societal impacts.

The graph representing polygenic inheritance is the one depicting the egg size frequency, as it shows a continuous range of traits, typical of polygenic inheritance. Polygenic traits are influenced by multiple genes, resulting in a bell-shaped curve in the distribution of phenotypes.

The blood groups frequency graph represents multiple allele inheritance, as it shows distinct categories (A, B, AB, O) with specific frequencies in the population. This trait is determined by multiple alleles at a single locus, where the presence of different alleles results in the different blood types.

In contrast, the egg size frequency graph illustrates polygenic inheritance, characterized by a continuous variation in traits, with a range of egg sizes depicted. Polygenic traits result from the interaction of several genes, leading to smooth gradation in phenotypes.

In summary, the key difference is that multiple alleles refer to variations at a single gene locus, while polygenic traits arise from multiple genes contributing to a single trait.

Highly variable genes, particularly those found in regions of tandem repeats such as STRs (Short Tandem Repeats), are critical in DNA fingerprinting. In forensic investigations, DNA samples from a crime scene can be compared to the DNA of suspects through PCR (Polymerase Chain Reaction) amplification of STR regions.

1. Sample Collection: DNA samples are obtained from a variety of sources, such as blood, hair, or saliva.

2. PCR Amplification: Regions of the DNA that are highly variable are amplified to generate sufficient DNA for analysis.

3. Gel Electrophoresis: The amplified DNA is then separated by size using gel electrophoresis, allowing visualization of the STR patterns.

4. Comparative Analysis: The resulting DNA profiles are compared; a match between samples indicates a potential connection between the suspect and the crime scene.

Through this method, forensic scientists can provide crucial evidence that assists in solving crimes and administering justice.