Endosymbiosis and genome evolution
BiologyEvolutionAges 17–18
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Three screens on how eukaryotic cells and genomes became more complex. Endosymbiosis: along a timeline, a host cell related to archaea engulfs an aerobic alpha-proteobacterium (the future mitochondrion) and later a eukaryote engulfs a cyanobacterium (the future chloroplast); watch genes move to the nucleus and open five evidence cards: double membranes, circular DNA, 70S ribosomes, binary fission and rRNA sequences. Gene families: duplicate genes, let the copies collect mutations, read the identity matrix and build the globin gene tree or your own, then solve a mystery family. Gene transfer: conjugation, transformation and transduction between bacterial species and the spread of antibiotic resistance.
Lesson: Origin of eukaryotic cells and genome evolution
What it shows
Mitochondria and chloroplasts descend from bacteria that lived inside other cells. About 2 billion years ago a host cell related to archaea engulfed an aerobic alpha-proteobacterium, and later a eukaryote engulfed a cyanobacterium; most of their genes moved to the nucleus. Double membranes, circular DNA, 70S ribosomes, binary fission and rRNA sequences are the evidence. Genomes also grow by gene duplication: copies diverge at a roughly constant rate and form families such as the globins. Bacteria also share genes by horizontal transfer. Dates, rates and gene-loss curves are simplified.
How to use
On Endosymbiosis, press Run or Next step to follow the timeline and choose an Evidence card to compare the organelles with bacteria. On Gene families, pick Globins, Build your own (Run, then Duplicate a gene) or Mystery, and read the identity matrix. On Gene transfer, choose the Mechanism, Donor and Recipient, press Transfer, then Add antibiotic; in Detective mode, find the species that received gene R.
Parameters you can change
- Screen Endosymbiosis, Gene families, Gene transfer
- Timeline step 1–6
- Evidence card None (timeline), Double membrane, Circular DNA, 70S ribosomes, Binary fission, Gene sequences
- Gene family Globin family, Build your own, Mystery family
- Transfer mechanism Conjugation, Transformation, Transduction
- Gene transfer mode Transfer lab, Gene detective
Questions to explore
- Why do scientists think the outer membrane of a mitochondrion came from the host cell?
- If two copies of a gene are 93 % identical and two others are 43 % identical, which pair was duplicated more recently?
- How can a gene for antibiotic resistance spread from one bacterial species to an unrelated one?
