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

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

1. Transcription: In this stage, the DNA sequence of a gene is copied into mRNA. RNA polymerase binds to the promoter region of the gene, unwinds the DNA helix, and synthesizes a complementary mRNA strand by adding RNA nucleotides. The result is a single-stranded mRNA molecule that carries the genetic information from the nucleus to the cytoplasm.

2. Translation: The mRNA then associates with a ribosome, where the sequence of nucleotides is read in sets of three called codons. Each codon corresponds to a specific amino acid. Transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome, which links them together in a chain based on the sequence of codons, forming a polypeptide. This polypeptide will then fold into a functional protein.

To model linkage in genetics, the following method was followed:

1. Selection of Traits: Two observable traits were selected for the study.
2. Parent Generation (P): Parents with different phenotypes for the chosen traits were crossed to create the F1 generation.
3. F1 Generation: The F1 offspring's phenotypes were recorded, confirming heterozygosity.
4. F2 Generation: The F1 individuals were self-fertilized to produce the F2 generation. The phenotypes of the F2 offspring were examined, and these results were recorded.
5. Analysis of Results: The observed ratios of the F2 traits were compared to expected Mendelian ratios to determine if linkage was present. If the offspring ratios deviated significantly from what is expected, it indicated that the traits were linked.

This investigation enhanced my understanding of linkage by demonstrating how genes located on the same chromosome can be inherited together. Prior to this, I believed that all traits assort independently as per Mendel’s law of independent assortment. However, through the results of the model linkage, I observed that certain traits did not segregate as expected, indicating that they are linked due to their proximity on the chromosome. This investigation also highlighted the importance of performing crosses and analyzing large numbers of offspring to accurately identify linkage patterns.

Genetic changes induced by human intervention have significantly impacted society in various ways:

1. Agricultural Advancements: Selective breeding and genetically modified organisms (GMOs) have led to increased crop yields and resistance to pests and diseases. This has helped in food security but raised concerns about biodiversity loss.

2. Medical Innovations: Genetic engineering has enabled the development of gene therapies for hereditary diseases. This has the potential to cure previously untreatable conditions and improve the quality of life for many individuals.

3. Ethical Considerations: The manipulation of genetic material has sparked ethical debates regarding genetic privacy and the modification of human embryos, raising concerns about the potential for eugenics and socio-economic disparities.

4. Ecological Effects: Genetic changes can lead to unintended consequences in ecosystems, such as the influence of GMOs on native populations and the creation of superweeds resistant to the chemicals used in agriculture.

Overall, while human intervention has led to remarkable advances, it has also resulted in ethical dilemmas and ecological challenges that society must navigate.

The graph representing polygenic inheritance is the one illustrating egg size frequency in chickens. This graph typically shows a continuous variation in traits, leading to a bell-shaped distribution, which characterizes polygenic traits.

The differences between the graphs relate to the type of inheritance each represents:

• Blood Groups Graph: This graph shows discrete categories, representative of multiple allelic inheritance as seen in human blood types (A, B, AB, O). The presence of more than two alleles results in a defined number of blood group phenotypes.

• Egg Size Frequency Graph: This graph depicts a continuous range of egg sizes, which is indicative of polygenic inheritance. Polygenic traits are influenced by multiple genes, leading to a more varied phenotype across a spectrum rather than distinct categories.

Thus, the blood group graph demonstrates discrete inheritance due to multiple alleles, while the egg size graph exemplifies continuous variation typical of polygenic inheritance.

DNA fingerprinting utilizes highly variable regions of DNA, known as short tandem repeats (STRs). STR analysis is conducted as follows:

1. Sample Collection: Biological samples such as blood, hair, or skin are collected from the crime scene.
2. DNA Extraction: DNA is isolated from these samples using chemical processes.
3. PCR Amplification: Specific regions of the DNA containing STRs are amplified using polymerase chain reaction (PCR).
4. Gel Electrophoresis: The amplified STRs are separated based on size through gel electrophoresis, resulting in a pattern unique to the individual.
5. Comparison: The obtained DNA profile is then compared to potential suspects or databases to establish identity.

This technique has proved invaluable in forensics, enabling the identification of individuals with high accuracy based on their unique genetic profile.