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

The information in DNA is converted into a polypeptide through the processes of transcription and translation:

1. Transcription:

   • The DNA strand unwinds and unzips at the gene of interest.
   • RNA polymerase synthesizes a complementary mRNA strand using the DNA template.
   • This results in a single-stranded mRNA molecule that carries the genetic code from the nucleus to the ribosome.

2. Translation:

   • The mRNA strand binds to a ribosome.
   • Transfer RNA (tRNA) molecules carrying specific amino acids recognize codons in the mRNA sequence.
   • Amino acids are linked together in the order dictated by the mRNA, forming a polypeptide chain that folds into a functional protein.

This entire process demonstrates the flow of genetic information from DNA to functional proteins.

To model linkage, the following steps can be outlined:

1. Selection of Traits:

   • Choose the traits to be studied (e.g., seed shape and color in pea plants).

2. Crossing Parental Plants:

   • Cross plants with known genotypes to observe offspring phenotypes.

3. Observation of Offspring:

   • Analyze the phenotypes of the offspring for variations to determine linkage.

4. Statistical Analysis:

   • Calculate the ratio of phenotypes among offspring.
   • If the traits assort together more frequently than expected under independent assortment, linkage is suggested.

This investigation deepened my understanding of linkage by demonstrating how certain genes are inherited together rather than independently. Observing the offspring ratios allowed me to grasp the concept of genetic linkage and how genes located close to each other on the same chromosome tend to be inherited together, influencing phenotypic traits.

Genetic changes due to human intervention have had profound impacts on society, including:

1. Agricultural Advances:

   • Genetic modification has led to the development of crops resistant to pests, diseases, and herbicides, allowing for increased agricultural productivity.

2. Health Concerns:

   • Genetic engineering in humans can lead to potential cures for genetic disorders, but it raises ethical concerns regarding gene editing and designer babies.

3. Environmental Impact:

   • The introduction of genetically modified organisms (GMOs) has caused shifts in ecosystems and biodiversity, raising questions about ecological balance.

These changes have sparked debates on ethical, environmental, and health-related issues, highlighting the need for responsible use of biotechnology.

The graph representing polygenic inheritance is the one depicting a continuous range of traits, such as egg size frequency, indicating multiple genes influence the characteristics with overlapping phenotypic expressions.

The blood groups frequency graph shows distinct categories (A, B, AB, O) which illustrate multiple allele inheritance, where more than two alleles exist for a trait. In contrast, the egg size frequency graph illustrates polygenic inheritance, where many genes contribute to a phenotype resulting in a continuous distribution.

• Multiple Allele Inheritance:
  Involves scenarios like blood types, where multiple alleles (IA, IB, i) interact.

• Polygenic Inheritance:
  Involves traits controlled by multiple genes, leading to a range of phenotypes (e.g., human height, egg size).

Highly variable genes, such as short tandem repeats (STRs), are used in DNA fingerprinting to identify individuals based on unique genetic profiles.

1. Sample Collection:

   • Collect DNA samples from crime scenes and suspects.

2. PCR Amplification:

   • Use polymerase chain reaction (PCR) to amplify specific STR regions from the DNA.

3. Gel Electrophoresis:

   • Separate the amplified DNA fragments by size using gel electrophoresis.

4. Analysis:

   • Compare patterns from different samples; the unique patterns can confirm or exclude a suspect's involvement in a crime.

An example would be using STR analysis in a criminal case to match DNA samples from a suspect to evidence left at a crime scene.