Why do you look like your parents but not exactly like either of them? The answer lies in molecular instructions passed down through generations — instructions so precise they predict eye colour, yet so flexible that no two people (except identical twins) share the same genetic blueprint.
Think about your own family. Write down three traits you share with a parent or sibling (e.g., eye colour, hair texture, height) and three traits that make you different from them.
Now answer: What do you think controls these similarities and differences? Is it just chance, or is there a biological system that passes information from one generation to the next?
Every living thing is shaped by information passed down from its parents — information written in a molecular code that has been copied, shuffled and transmitted for billions of years.
Genetics is the branch of biology that studies how this information is passed from one generation to the next (heredity) and why individuals within a species are not identical (variation).
Think of genetics as the instruction manual for building and running a living organism. Just as a builder follows architectural plans to construct a house, cells follow genetic instructions to build proteins, regulate processes and determine traits. But unlike a house plan, genetic instructions can be shuffled and recombined every generation — which is why you are not a clone of either parent.
Australian Merino sheep are one of the world's finest examples of selective breeding — a practice that predates modern genetics but applies the same principles. In the early 1800s, John Macarthur imported Spanish merinos to Australia and selectively bred sheep with the finest wool. Today, Australian merinos produce wool with fibre diameters as fine as 15 microns — roughly one-fifth the thickness of a human hair. This was achieved by choosing which animals reproduced based on heritable traits, exactly the kind of decision-making that genetics explains at the molecular level.
The genetic information in your body is organised like a library: molecules group into genes, genes group into chromosomes, and chromosomes sit inside every cell nucleus.
To understand genetics, you need to grasp the relationship between four key structures:
If you cut your hair, dye it pink or build muscle at the gym, those changes do not alter your DNA — and they will not be passed to your children.
Inherited traits are determined by genes passed from parents to offspring. Examples include blood type, natural eye colour, attached or detached earlobes, and tongue-rolling ability.
Acquired characteristics are changes that occur during an organism's lifetime due to environment, behaviour or accident. Examples include scars, tattoos, tanned skin, learned languages and muscle mass from training.
This distinction is crucial because it was at the heart of one of the biggest mistakes in biology history. In the 1800s, Jean-Baptiste Lamarck proposed that acquired characteristics could be inherited — for example, that giraffes stretched their necks and passed longer necks to offspring. We now know this is false. Only changes to DNA (mutations) can create heritable variation.
Australian sprinting legend Cathy Freeman won gold in the 400m at the Sydney 2000 Olympics. While training and dedication were essential, genetics also played a role. Research shows that variants of the ACTN3 gene (often called the "speed gene") influence whether muscle fibres are optimised for explosive power or endurance. About 18% of the global population carry two copies of a variant that produces less alpha-actinin-3 protein, making them less suited to sprinting. Cathy Freeman, like most elite sprinters, likely carried the "power" variant — but her success was still the result of genetics plus extraordinary training, diet and mental toughness.
Wrong: "If parents work out and get muscular, their children will be born muscular."
Right: Acquired characteristics like muscle mass from exercise do not change DNA. However, parents can pass genes that make it easier to build muscle. The children inherit the genetic potential, not the parent's actual muscles.
If every organism in a species were identical, the entire population could be wiped out by a single disease, one climate shift or one predator adaptation.
Variation is the presence of differences in traits among individuals of the same species. It arises from two main sources at this stage:
Variation is not just interesting — it is essential. In Unit 1, you will learn how variation provides the raw material for natural selection and evolution. Without variation, populations cannot adapt to changing environments.
Since 1996, Tasmanian devils have faced a contagious cancer (Devil Facial Tumour Disease, DFTD) spread by biting. Because devil populations had very low genetic diversity, the cancer could infect nearly every individual it contacted. Conservation programs are now selectively breeding devils with natural resistance and releasing them to boost genetic variation in wild populations. This is a powerful example of why variation matters for survival.
1 A scar from a skateboard accident
2 Blood type (A, B, AB or O)
3 Ability to speak Mandarin
4 Dimples when smiling
5 Tanned skin after a summer at Bondi Beach
1 Can you roll your tongue? Record for yourself and your family member.
2 Do you have attached or detached earlobes? Is this the same or different from your family member?
3 Explain why two siblings with the same parents can still look different. Use the words gene, allele and variation in your answer.
1. Which statement best defines heredity?
2. What is the correct relationship between DNA, genes and chromosomes?
3. A person has brown eyes, while their sibling has blue eyes. Both have the same parents. What best explains this difference?
4. An Australian farmer selectively breeds Merino sheep with the finest wool. Which concept does this practice rely on?
5. Why is genetic variation important for the survival of a species?
6. Define genetics and explain why it is an important area of scientific study. In your answer, refer to both heredity and variation. 3 MARKS
7. Distinguish between a gene, an allele and a chromosome. Use an example involving eye colour to illustrate your answer. 4 MARKS
8. Explain why offspring resemble their parents but are never identical to either parent (except identical twins). In your answer, refer to alleles, sexual reproduction and variation. 5 MARKS
Go back to your Think First responses at the top of the lesson.
1. Scar from skateboard accident: Acquired. The scar is caused by physical injury and tissue repair. It does not change DNA and cannot be passed to offspring.
2. Blood type: Inherited. Blood type is determined by alleles of the ABO gene inherited from both parents.
3. Ability to speak Mandarin: Acquired. Language is learned through exposure and education. It is not coded in DNA.
4. Dimples: Inherited. Dimples are caused by variations in facial muscle structure controlled by genes.
5. Tanned skin: Acquired. Tanning is the skin's response to UV exposure (melanin production). It does not change DNA and is not inherited.
3. Why siblings look different: Siblings inherit different combinations of alleles from their parents because of sexual reproduction [1 mark]. Each parent passes on only half of their alleles to each offspring, and which half is random [1 mark]. This means two siblings can inherit different alleles for the same gene — for example, one sibling might get the brown-eye allele from mum and the blue-eye allele from dad, while another sibling gets blue from both [1 mark]. This genetic shuffling creates variation within a family [1 mark].
1. B — Heredity is the passing of traits from parents to offspring. Option A defines variation. Option C defines mutation. Option D defines adaptation/evolution.
2. C — Chromosomes are structures made of DNA and proteins. Genes are segments of that DNA. Option A is backwards. Option B is completely backwards. Option D is incorrect — they are related structures, not separate molecules.
3. A — Siblings receive different combinations of alleles due to the random assortment of chromosomes during gamete formation. Option B confuses acquired characteristics with inheritance. Option C is biologically impossible — siblings have the same number of chromosomes. Option D is false — eye colour is strongly genetic.
4. D — Selective breeding relies on heritable traits controlled by genes. Option A describes Lamarckism, which is incorrect. Option B ignores the genetic component. Option C contradicts the existence of variation.
5. B — Variation provides different traits, some of which may be advantageous in changing environments or against diseases. Option A is wrong — identical individuals would be more vulnerable. Option C is false — variation matters for all species. Option D is incorrect — variation does not automatically eliminate disease.
Q6 (3 marks): Genetics is the scientific study of heredity and variation in living things [1 mark]. It is important because understanding heredity allows us to predict and explain how traits are passed between generations, which is essential in medicine, agriculture and conservation [1 mark]. Understanding variation is equally important because it explains why individuals differ and provides the raw material for populations to adapt and survive environmental changes [1 mark].
Q7 (4 marks): A gene is a segment of DNA that codes for a specific trait or protein [1 mark]. An allele is a version or variant of that gene — for example, the gene for eye colour has brown, blue and green alleles [1 mark]. A chromosome is a structure made of DNA and proteins that contains many genes packaged together [1 mark]. For example, the eye colour gene is located on chromosome 15. A person might inherit a brown-eye allele from one parent and a blue-eye allele from the other [1 mark].
Q8 (5 marks): Offspring resemble their parents because they inherit genes and alleles from both parents through sexual reproduction [1 mark]. However, they are not identical to either parent because each offspring receives a unique combination of alleles [1 mark]. During reproduction, each parent contributes only half of their chromosomes (23 in humans), and which chromosomes are passed on is random [1 mark]. This means siblings can inherit different alleles for the same genes — one might get a brown-eye allele where another gets a blue-eye allele [1 mark]. This genetic shuffling creates variation, ensuring that every sexually reproduced individual has a unique genetic blueprint (except identical twins, who come from the same fertilised egg) [1 mark].
Test your knowledge of heredity, DNA, genes and variation in this fast-paced quiz battle. Correct answers power your attacks!
Climb platforms using your knowledge of DNA, genes, chromosomes and alleles. Pool: Lesson 1.
Tick when you have finished all activities and checked your answers.