Preview
IB DP Biology — Unit D: Continuity and Change | SL | D1.3 Genomics and Advanced Biotechnology
📋 What You Will Learn
- Identify the key findings of genome sequencing projects, including the human genome, and explain what they reveal about genome organisation
- Explain the nature and significance of transposable elements — what they are, how they move, and why they matter for genome evolution
- Describe the principles and applications of CRISPR-Cas9 as a gene-editing tool, including its mechanism and biological basis
- Analyse data from genome comparisons and biotechnology experiments to draw conclusions about gene function and evolutionary relationships
- Evaluate the ethical implications of genome editing and the use of personal genomic data in medicine and research
🔍 Guiding Question How has our ability to read, compare, and edit genomes transformed our understanding of life — and what responsibilities does that power create?
🌍 Why This Matters In 2003, scientists completed the first full sequence of the human genome — three billion base pairs, decoded after thirteen years and three billion dollars. Today, a personal genome can be sequenced in hours for under a thousand dollars. That shift from impossibility to routine has opened an era in which we can not only read the genome but rewrite it — raising questions about what it means to be human, who controls genetic information, and how far biological intervention should go.
What Is a Genome — and Why Sequence It?
Before we can edit or compare genomes, we need to read them. Genome sequencing is the process of determining the precise order of nucleotide bases across an entire organism's DNA. The results are consistently surprising: genomes are far larger, stranger, and more repetitive than early biologists expected.
📖 Key Definition — Genome The complete set of genetic information of an organism, including all of its DNA — both coding and non-coding sequences. In eukaryotes, this includes nuclear chromosomal DNA, mitochondrial DNA, and (in plants) chloroplast DNA.
📖 Key Definition — Genome Sequencing The process of determining the complete nucleotide base sequence of an organism's genome. Modern sequencing uses next-generation sequencing (NGS) technologies that read millions of short DNA fragments simultaneously and assemble them computationally.
The Human Genome Project (HGP), completed in 2003, was the first large-scale effort to sequence an entire human genome. It revealed that the human genome contains approximately 3.2 billion base pairs, organised across 23 pairs of chromosomes. Yet only about 1.5% of that sequence codes for proteins. The rest — once dismissed as "junk DNA" — turns out to be biologically active in ways we are still discovering.
Key Findings from Genome Sequencing Projects
Genome sequencing has overturned many assumptions about how genetic information is organised. The human genome contains approximately 20,000–25,000 protein-coding genes — far fewer than the 100,000 predicted before sequencing began. This is comparable to the gene count of a nematode worm ( Caenorhabditis elegans ), which has roughly 20,000 genes despite being vastly less complex. Complexity, it turns out, does not arise simply from having more genes.
A striking finding is that a large proportion of eukaryotic genomes consists of repetitive sequences. In humans, over 50% of the genome is made up of repeated elements, many of which are derived from transposable elements. Non-coding RNA genes, regulatory sequences, introns, and pseudogenes account for much of the remaining non-coding DNA. Far from being inert, these sequences regulate gene expression, influence chromosome structure, and drive genome evolution.
- Human genome: ~3.2 billion base pairs; ~20,000–25,000 protein-coding genes; ~1.5% coding sequence
- E. coli genome: ~4.6 million base pairs; ~4,300 genes; ~88% coding sequence
- Arabidopsis thaliana (plant): ~135 million base pairs; ~27,000 genes
- Puffer fish ( Fugu rubripes ): ~365 million base pairs — much smaller than human genome but similar gene count, due to less repetitive DNA
Comparative Genomics
Comparing genomes across