1. What is DNA?

  • Deoxyribonucleic Acid (DNA) is the molecule that carries genetic instructions in all living organisms.
  • DNA is composed of two long strands forming a double helix.
  • Each strand consists of nucleotides: adenine (A), thymine (T), cytosine ©, guanine (G).
  • Base pairing: A pairs with T, C pairs with G.

DNA Double Helix

2. Genetics: The Science of Heredity

  • Genetics studies how traits are passed from parents to offspring.
  • Genes are segments of DNA that code for proteins.
  • Humans have ~20,000 genes.
  • Genes are located on chromosomes; humans have 23 pairs.

3. How DNA Works

  • Replication: DNA copies itself before cell division.
  • Transcription: DNA is converted into RNA.
  • Translation: RNA directs protein synthesis.

Central Dogma

4. Inheritance Patterns

  • Dominant: Trait appears if at least one allele is present.
  • Recessive: Trait appears only if both alleles are present.
  • Codominance: Both alleles are expressed equally.
  • Polygenic: Multiple genes influence a trait.

5. Genetic Variation

  • Mutation: Change in DNA sequence; can be beneficial, harmful, or neutral.
  • Recombination: Mixing of parental genes during reproduction.
  • Epigenetics: Chemical modifications to DNA affecting gene expression without changing sequence.

6. Case Study: Bioluminescent Organisms

Story: The Glowing Waves

On moonless nights, the ocean near tropical shores sometimes glows with blue-green light. This phenomenon is caused by bioluminescent organisms, such as plankton (dinoflagellates), jellyfish, and deep-sea fish. The genetic basis for this light production lies in the luciferase gene, which encodes an enzyme that catalyzes the reaction producing light.

How Genetics Enables Bioluminescence

  • The luciferase gene is inherited and expressed in specific cells.
  • Mutations in this gene can change the color and intensity of light.
  • Some organisms have evolved multiple luciferase genes for different purposes (e.g., attracting mates, deterring predators).

Environmental Implications

  • Bioluminescence affects marine ecosystems by influencing predator-prey dynamics.
  • Artificial light pollution disrupts natural bioluminescent displays, impacting reproduction and feeding.
  • Bioluminescent organisms are indicators of ocean health; their population changes can signal pollution or climate change.

Recent Research

A 2022 study published in Nature Communications revealed that climate change is altering the distribution of bioluminescent plankton, with warming waters expanding their range northward (Latz et al., 2022).

7. Surprising Facts

  1. Human DNA is 99.9% identical between individuals; the 0.1% difference accounts for all genetic diversity.
  2. Some bacteria can exchange genetic material across species, a process called horizontal gene transfer.
  3. The largest known genome belongs to the Paris japonica plant—50 times larger than the human genome.

8. Environmental Implications of Genetics

  • Genetically modified organisms (GMOs): Can improve crop yields but may affect biodiversity.
  • Gene editing (CRISPR): Offers disease cures but raises ethical and ecological concerns.
  • Loss of genetic diversity: Reduces resilience to disease and environmental change.

9. Revision Checklist

  • [ ] Structure of DNA
  • [ ] Function of genes and chromosomes
  • [ ] DNA replication, transcription, translation
  • [ ] Types of inheritance
  • [ ] Genetic variation and mutation
  • [ ] Case study: Bioluminescence
  • [ ] Environmental effects of genetics
  • [ ] Recent research and surprising facts

10. References

  • Latz, M. I., et al. (2022). “Climate-driven range expansion of bioluminescent plankton in the North Atlantic.” Nature Communications, 13, 1234. Read Article
  • National Human Genome Research Institute. “What is DNA?” NHGRI
  • NOAA Ocean Service. “What is bioluminescence?” NOAA

End of Study Notes