Homozygous Dominant × Recessive
Lesson notes
Overview
Crossing AA with aa gives all Aa offspring showing the dominant trait. This topic is rated beginner and is number 59 of 110 in Biology. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows a living system animated over time. 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
Crossing a homozygous dominant parent, AA, with a homozygous recessive parent, aa, gives offspring that are all heterozygous, Aa, and since A is dominant they all show the dominant trait. This was Mendel’s first generation, where all the offspring of tall and short pea plants were tall. The recessive trait seems to vanish but returns in the next generation when the Aa offspring are crossed, which showed that the factors do not blend.
Reading the relationship
The expression "AA × aa → 100% Aa" is a compact summary of the idea. It uses the symbols A, a; name what each one stands for before you start. 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 “Brain Size Through Hominin History”, the topic before it in Biology. Once you are comfortable, continue with “Test Cross”.
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 “Homozygous Dominant × Recessive” 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 Homozygous Dominant × Recessive?
Crossing AA with aa gives all Aa offspring showing the dominant trait. It is a beginner topic in Biology.
How do I use the Homozygous Dominant × Recessive simulation?
The panel at the top shows a living system animated over time. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression AA × aa → 100% Aa 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 “Brain Size Through Hominin History”, 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.