KS3 · Biology
Heritable variation and selection
Identical twins share the same genetic material, yet you can still tell them apart. So which features can actually be passed on?
Commit, then check
Look at the three dogs: a bulldog, a Chihuahua and a Great Dane. They differ in size, type of fur, muscle mass, ears and tails.
Are they three different species, or one?
Why genetic variation is heritable
Reason it through
Why can genetic variation be passed on to offspring?
First link · your turn
Every cell an organism is made of holds something that stores instructions. What is it, and where is it kept in animal and plant cells?
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
What you need to know
- Variation means differences in the features of individuals of the same species.
- Some variation is caused by the environment: the surroundings of an organism, such as temperature, sunlight, pollutants, nutrients or soil pH.
- Some variation is caused by lifestyle: what a person does and chooses, such as diet, exercise, a tattoo or a nose piercing.
Have a goYour friend insists a new nose piercing counts as 'environmental variation' because it's on her face. Which kind is it, and what would you say?
Lifestyle variation. Environment means surroundings; a piercing is something a person chooses to do to their body.
Environment is the surroundings of an organism, such as sunlight or soil pH, while lifestyle is what a person does and chooses.
- Some variation is caused by genetic information stored in genetic material, which is made of DNA.
- Variation caused by the environment or lifestyle is not heritable, so it cannot be passed on to offspring.
Have a goYour classmate is confidently wrong: 'My aunt's tattoo is so cool, my cousin will definitely be born with one.' Is she right?
No. A tattoo is lifestyle variation, so it can't be passed on to offspring.
Variation caused by lifestyle is not heritable, however much the parent likes the tattoo.
- Genetic variation is heritable because genetic material is passed from parents to offspring through reproduction.
- Only features that result from instructions in genetic material can be inherited, such as natural eye colour or blood type.
- Most traits come from a combination of genetic, environmental and lifestyle factors, such as body mass, plant size and height.
Have a goBody mass comes from genes, environment and lifestyle combined. Name one lifestyle factor that could affect a person's body mass.
Diet, or how much exercise they do.
Lifestyle is what a person does and chooses, such as diet and exercise, so these can add to what their genes contribute.
- Identical twins share genetic material but are not exactly the same, because environment and lifestyle cause variation between them.
The big picture
Features differ between individuals of the same species, and that is called variation. Some variation comes from genetic information, some from the environment and some from lifestyle. Only variation from genetic material is heritable, but most traits combine all three causes.
Key points
Worked example
Problem
Sam has natural brown hair, a nose piercing and blood type O. Which of these features could Sam pass on to a child, and which could not?
⚠ Watch out
Thinking any feature a parent has can be passed on, even one they gained during their life, such as a scar, a tattoo or muscles built by exercise. Only features that result from the instructions in genetic material can be inherited.
Memory hook
Ask of any feature: was it in the instructions, or did it happen to me? Only the instructions get passed on.
Check yourself
Pick a feature of your own, such as your height. Which of the three causes could be behind it: genetic information, environment, lifestyle? How would you decide which part could be passed on?
Flashcards
(12)What is variation?
What is the environment, in the topic of variation?
What is lifestyle variation?
Is variation caused by the environment or lifestyle heritable?
What is genetic material made of, and where is it stored in animal and plant cells?
What does genetic material store instructions for?
Why is genetic variation heritable?
Name three features that result from instructions in genetic material.
What controls the sex of the offspring in many turtle species?
What controls the colour of hydrangea flowers?
Why do most traits not have a single cause?
Identical twins: what is the same, and why are they not exactly alike?
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
Learning with Lightbulb is opening soon
You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.
Keep me postedMore KS3 Biology topics
- A balanced diet
- A healthy pregnancy
- Adaptations of leaves: stomata and gas exchange
- Adaptations of organisms to their environment
- Adaptations of predators and prey
- Agriculture and habitat loss
- Animal adaptations to environment
- Animal cell structure and functions
- Asthma and the lungs
- Bacteria in the human digestive system
- Biomechanics: forces in the skeleton
- Breathing, respiration and gas exchange
How this lesson was checked. This KS3 Biologylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 9 October 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.