Specimen Prep - Molecular Basis of Inheritance

Specimen Prep Guide: Molecular Basis of Inheritance

Key Concepts (Recall & Understanding)

• The Genetic Material: Know the properties of a genetic material and the experiments that proved DNA as the genetic material (Griffith, Hershey-Chase).
• DNA Structure: Understand the structure of a polynucleotide chain and the double helix model of DNA proposed by Watson and Crick.
• DNA Replication: Know the semi-conservative model of DNA replication and the enzymes involved.
• Transcription & Translation: Understand the processes of transcription (synthesis of RNA from DNA) and translation (synthesis of protein from mRNA).
• Gene Regulation: Understand the lac operon model of gene regulation in prokaryotes.
• Human Genome Project & DNA Fingerprinting: Know the goals of the HGP and the principle of DNA fingerprinting.

Application Corner

• Problem Type: If a DNA molecule has 20% adenine, what is the percentage of guanine? (Answer: 30%).
• Example: Transcribing a given DNA sequence into mRNA and then translating it into an amino acid sequence using a codon table.

Analytical Thinking

• Scenario: A DNA sample from a crime scene is compared with the DNA of two suspects. How can DNA fingerprinting help identify the culprit?
• Analysis: The pattern of VNTRs (Variable Number of Tandem Repeats) in the DNA fingerprint will be unique for each individual. The suspect whose DNA fingerprint matches the one from the crime scene is likely the culprit.
• Diagram Interpretation: Be able to identify the components of a transcription unit (promoter, structural gene, terminator).

Key Experiment

• Meselson and Stahl's Experiment: This experiment proved that DNA replication is semi-conservative. They used heavy nitrogen (¹⁵N) to distinguish between the parent and newly synthesized DNA strands.

Assertion-Reason Practice

1. Assertion: The genetic code is unambiguous and specific. Reason: One codon codes for only one amino acid.

   • (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

2. Assertion: In the lac operon, the structural genes are switched off when the repressor is bound to the operator. Reason: The repressor prevents the RNA polymerase from transcribing the structural genes.

   • (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

HOTS (Higher-Order Thinking Skills) Question

• Why is the genetic code said to be "degenerate"?
  • Answer: Because some amino acids are coded for by more than one codon. This provides a buffer against mutations, as a change in the third base of a codon may not change the amino acid being coded for.