Gel Electrophoresis
Lesson notes
Overview
An electric field pulls DNA fragments through a gel, with small pieces moving farthest. This topic is rated beginner and is number 19 of 110 in Biology. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
Gel electrophoresis separates DNA fragments by size. DNA is negatively charged, so in an electric field it moves through a gel towards the positive electrode, and the gel acts like a sieve: small fragments move farthest, large ones lag behind. The distance travelled is roughly proportional to the logarithm of the size. A ladder of known sizes is run alongside for comparison, and a dye shows the bands. It is used in DNA fingerprinting, genetic testing and checking PCR products.
Reading the relationship
The expression "distance ∝ 1/log(size)" is a compact summary of the idea. It uses the symbols d, i, s, t, a, n; name what each one stands for before you start. Notice that it contains a ratio, so increasing the denominator makes the result smaller, and a logarithm, which turns multiplication into addition and compresses large values. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Start by only moving one slider at a time. Say aloud what you expect, then check.
Common pitfalls
Biological processes are rarely all-or-nothing. Look for the feedback, the timing and the exceptions, rather than learning a single fixed sequence by heart.
How it connects
It builds on “PCR Exponential Amplification”, the topic before it in Biology. Once you are comfortable, continue with “Cell Structure”.
Why it matters
Biology shows how living things are built and how they work, grow, inherit traits and adapt.
Where you might use it
- Revising “Gel Electrophoresis” before a class, exam or certification
- Understanding inherited conditions, medicines and how the body responds to disease
- Working in farming, conservation and food production, where populations and genes matter
- Following news about vaccines, genetic testing and climate effects on wildlife
Frequently asked questions
What is Gel Electrophoresis?
An electric field pulls DNA fragments through a gel, with small pieces moving farthest. It is a beginner topic in Biology.
How do I use the Gel Electrophoresis simulation?
The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression distance ∝ 1/log(size) packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Core ideas and first intuitions. No prior knowledge needed. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “PCR Exponential Amplification”, the previous topic in Biology. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.