Inheritance, variation and evolution
Genetics explains why offspring resemble their parents without being identical, and evolution explains how that variation reshapes species over time.
Lesson overview
What you'll learn in this lesson
Explain inheritance, variation, evolution and ecological relationships at GCSE standard.
Key learning points
- • DNA, genes and meiosis
- • Genetic crosses
- • Evolution by natural selection
This lesson at a glance
- 30 minutes
- 20 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 20
Visual introductionPicture this
Inheritance, variation and evolution
Genetics explains why offspring resemble their parents without being identical, and evolution explains how that variation reshapes species over time.
In a nutshell
Explain inheritance, variation, evolution and ecological relationships at GCSE standard.
Learning cycle
Part 2 of 20
Learning cycle 1 of 2
Part 1 · DNA, genes and meiosis
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 20
Learn
DNA, genes and meiosis
DNA is a double helix carrying genes that code for proteins; the full set is the genome. Meiosis produces four genetically different gametes with half the chromosome number, so fertilisation restores the full set while creating variation. Mitosis, by contrast, produces identical cells for growth and repair.
Reset break
Part 4 of 20
Pause
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Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 20
Learn
Genetic crosses
Alleles may be dominant or recessive; genotype is the alleles present and phenotype the characteristic shown. A Punnett square predicts proportions, not guarantees: a 3 : 1 ratio is a probability for each offspring. Inherited disorders such as cystic fibrosis and polydactyly are standard examples.
Quick check
Part 6 of 20
Quick check
Part 7 of 20
Reset break
Part 8 of 20
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 20
Learning cycle 2 of 2
Part 2 · Evolution by natural selection
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 20
Learn
Evolution by natural selection
Variation exists within a population; individuals with advantageous characteristics are more likely to survive, reproduce and pass on those alleles, so over many generations the population changes. Evidence comes from fossils and from observed antibiotic resistance in bacteria. Selective breeding and genetic engineering apply the same principles deliberately.
Quick check
Part 11 of 20
Reset break
Part 12 of 20
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 20
Explore the idea
Part 14 of 20
Worked example
Worked answer: two carriers of a recessive disorder have a child. Give the probability it is affected (3 marks)
Both parents are heterozygous, Aa (1). A Punnett square of Aa × Aa gives AA, Aa, Aa and aa (1). Only aa shows the disorder, so the probability is 1 in 4, or 25% (1). Note this is a probability for each child independently, not a guarantee that one in every four children will be affected.
Challenge round
Part 15 of 20
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 16 of 20
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 20
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Meiosis produces four genetically different gametes with half the chromosome number, so fertilisation restores the full set while creating ____.
Challenge round
Part 18 of 20
Game · Recall cards
Meiosis produces
Card 1 of 4
Mastery quiz
Part 19 of 20
Marked quiz
End of lesson quiz: Inheritance, variation and evolution
4 questions, marked with the reasoning shown. No timer.
1. Meiosis produces
2. Genotype refers to
3. Antibiotic resistance spreads because resistant bacteria
4. A cross of Aa × Aa gives affected offspring with probability
Lesson round-up
Part 20 of 20
Lesson round-up
Ready when you are
Quiz score
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Points this lesson
0
Best run
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Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 20 · Watch & discover