DNA & GENOME

DNA & Genome

1. What is DNA?

  • DNA = Deoxyribonucleic Acid.
  • DNA is the genetic material of most living organisms.
  • It can be understood as:
    • Code of life → contains instructions for making and maintaining an organism.
    • Vehicle of heredity → carries genetic information from parents to offspring.
  • DNA contains genes, which carry instructions mainly for making proteins.
  • In humans, most DNA is present in the nucleus.

2. What is a Chromosome?

  • A chromosome is a thread-like structure made mainly of DNA + proteins.
  • It carries genetic information.
  • Humans normally have 46 chromosomes = 23 pairs.
    • 22 pairs → autosomes.
    • 1 pair → sex chromosomes.
  • Female: XX.
  • Male: XY.
  • Human chromosomes together contain about 3.2 billion base pairs of DNA.

3. What is a Genome?

  • Genome = complete set of genetic material/DNA of an organism.
  • It includes:
    • Genes.
    • Non-coding regions.
  • The human genome is distributed mainly across 23 pairs of chromosomes.

4. Building Blocks of DNA

The basic unit of DNA is called a nucleotide.

Each nucleotide has 3 parts:

  1. Deoxyribose sugar.
  2. Phosphate group.
  3. Nitrogenous base.

5. Mitochondrial DNA (mtDNA)

  • DNA is found mainly in the nucleus, but mitochondria also contain DNA.
  • This is called mitochondrial DNA (mtDNA).
  • Mitochondria are called the powerhouses of the cell because they produce ATP ATP (Adenosine Triphosphate) is the main energy currency of the cell, providing energy for cellular activities.

6. What is RNA?

  • RNA = Ribonucleic Acid.
  • Usually single-stranded.
  • RNA helps in protein synthesis.

7. Genes & Human Genome

  • A gene is a functional segment of DNA containing information needed to produce a functional product, often a protein.
  • Humans have approximately 20,000 protein-coding genes.
  • Only about 1–2% of the human genome directly codes for proteins.
  • The remaining DNA includes many non-coding regions with important regulatory and other functions.

8. Epigenetics

What is epigenetics?

  • Epigenetics = changes in gene activity/expression without changing the DNA sequence itself.
  • Almost all cells in the body contain essentially the same genome.
  • Yet cells have different structures and functions.

Why?

Because different genes are switched ON or OFF in different cells.

For example:

  • Heart cells express genes needed for heart function.
  • Kidney cells express genes needed for kidney function.

9. Applications of Genome Sequencing

Medical

  • Detect genetic mutations.
  • Diagnose some inherited disorders.
  • Help understand cancers.
  • Support personalised medicine.

Agriculture

  • Identify genes responsible for desirable traits.
  • Help in selective breeding of crops and livestock.

Prenatal Screening

  • Can help detect certain genetic/chromosomal abnormalities in a fetus.

Forensics

  • DNA information can help:
    • Identify individuals.
    • Establish biological relationships such as paternity.

Evolution

  • Helps study evolutionary relationships and ancestry.

10. Genetic Variation / Polymorphism

  • Humans are genetically very similar, but individuals still have many DNA differences.
  • A genetic variant is a difference in DNA sequence between individuals.
  • Polymorphism generally refers to a genetic variation that is relatively common in a population.
  • Variations can influence:
    • Physical traits.
    • Disease susceptibility.
    • Response to medicines.
    • Ancestry.
    • Biological relationships.

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