Introduction to Genetics and Heredity
In 1865, Gregor Mendel counted 7,324 pea plant offspring to discover why traits disappear and reappear across generations.
Printable Worksheets
Print or save as PDF, or build a custom worksheet from any module's questions.
Q1 · What do you already know about how traits are passed from parents to children?
Think about physical features like eye colour, hair colour or height, what makes children look like their parents?
Q2 · If two parents both have brown eyes but their child has blue eyes, what does this suggest about how inheritance works?
Consider what must be true about the parents' genes if they can produce a child with a trait neither parent shows.
● Know
- Definitions of genetics, heredity, DNA, gene, chromosome, allele and trait
- That living things reproduce and pass characteristics to offspring
- That genetic variation exists between individuals of the same species
● Understand
- How genetic information is passed from parents to offspring
- Why offspring resemble but are not identical to their parents
- The relationship between DNA, genes, chromosomes and traits
● Can do
- Distinguish between inherited and non-inherited traits
- Use basic genetic vocabulary correctly in explanations
- Identify sources of genetic variation in a population
Look at a parent and child standing side by side: the same nose, the same eye colour, yet something slightly different every time, never a perfect copy. Genetics is the branch of biology that explains why offspring resemble their parents, but never perfectly. Every organism carries genes, which are segments of DNA that act as instructions for building and running the body. Each gene can exist in different versions called alleles, and you inherit one allele from your mother and one from your father for most traits.
A trait is any observable characteristic, such as height, earlobe attachment or the ability to taste certain chemicals. Traits are influenced by genes, but also by environment, identical twins with the same genes can differ in weight if one exercises more. Heredity is the overall process by which these genetic instructions travel from one generation to the next. Understanding heredity is the foundation for everything in this unit, from DNA structure to evolution.
Eye colour is a classic genetic trait. The gene involved produces a pigment called melanin. A high-melanin allele gives brown eyes, while a low-melanin allele gives blue eyes. If you inherit one of each, the brown allele usually masks the blue one, which is why two brown-eyed parents can still have a blue-eyed child if both carry a hidden blue allele.
Australian research: CSIRO scientists study genetic diversity in native plants to help agriculture adapt to climate change. By understanding which genes control drought resistance, they can help farmers breed crops that survive Australia's harsh conditions without relying on extra water.
Students often think heredity means identical copying, that children are exact mixtures of their parents. In reality, each child receives a random half of each parent's genes, and small copying errors (mutations) introduce new variation. This is why siblings share about 50% of their DNA but look and behave differently.
Tap each card to flip. Mark Got it when you can recall the answer without flipping.
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.
To talk precisely about inheritance, we need two key terms: genotype and phenotype. Your genotype is the actual genetic code you carry, the combination of alleles hidden inside your cells. Your phenotype is what we can see or measure: your height, your blood type, whether you can roll your tongue. The same genotype can produce different phenotypes depending on the environment, but the genotype sets the boundaries.
Every gene sits at a specific location on a chromosome, and humans have 23 pairs of chromosomes. Because chromosomes come in pairs, you have two copies of almost every gene, one from Mum, one from Dad. These paired genes may carry the same allele or different alleles. When they differ, the interaction between them (dominant versus recessive) determines the phenotype you actually display.
Consider the gene for earlobe attachment. The free-earlobe allele is dominant; the attached-earlobe allele is recessive. If your genotype is one of each (heterozygous), your phenotype will be free earlobes because the dominant allele masks the recessive one. Only someone with two recessive alleles (homozygous recessive) will show attached earlobes.
Australian context: Researchers at the University of Queensland use twin studies to separate genetic from environmental influences on traits. By comparing identical and non-identical twins raised in the same Australian communities, they can estimate how much of a trait like reading ability or anxiety is inherited versus learned.
One of the most important ideas in genetics is that heredity is not photocopying. When parents reproduce sexually, their chromosomes are shuffled and divided into gametes (sperm and egg cells). Each gamete carries a random half of that parent's genes. When sperm meets egg, the resulting embryo gets a unique combination that has never existed before and will never exist again, unless you have an identical twin.
This shuffling is why siblings can be so different. You and your brother might share 50% of your DNA on average, but the specific 50% you each inherited is random. One sibling might get Dad's curly-hair allele and Mum's straight-hair allele; another might get the opposite. Add to this the influence of environment, nutrition, sunlight, exercise, and the outcome is even more variety.
Imagine a deck of cards where red cards represent Mum's alleles and black cards represent Dad's. Each child draws half the deck at random. Two draws from the same deck will almost always produce different hands. Genetics works the same way: each child gets a different hand from the same parental deck.
Australian agriculture: Merino sheep in Australia are famous for their fine wool. Farmers have used selective breeding for over 200 years to improve fleece quality, but they still get variation in each generation. This natural genetic shuffle is both a challenge and an opportunity, it means there is always a chance of producing an exceptional animal.
Many students believe that dominant alleles are 'stronger' or more common in the population. Dominance only describes which allele is expressed when both are present; it says nothing about how frequent the allele is. In fact, many dominant alleles are rare (such as Huntington's disease), while many recessive alleles are extremely common (such as the allele for blue eyes in some populations).
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 and are not inherited. Only genetic traits encoded in DNA can be passed to offspring.
Wrong: "If a parent builds muscle through exercise, their children will automatically have bigger muscles because the gained muscle was 'recorded' in their DNA."
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.
Tasmanian Devils and Facial Tumour Disease
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.
Inherited or Acquired?
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
Family Trait Survey
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.
Copy Into Your Book
▼Core Definitions
- Genetics = study of heredity and variation
- Heredity = passing traits from parents to offspring
- Variation = differences between individuals
- DNA = molecule carrying genetic instructions
- Gene = DNA segment for one trait
- Chromosome = package of many genes
- Allele = version of a gene
The Hierarchy
- DNA contains genes
- Genes are packaged into chromosomes
- Chromosomes are in the nucleus of every cell
- You inherit two alleles per gene (one from each parent)
Inherited vs Acquired
- Inherited = genetic, passed in DNA
- Acquired = environmental, not in DNA
- Acquired characteristics are NOT inherited
- Lamarck was wrong about this
Why Variation Matters
- Sexual reproduction shuffles alleles
- Mutations create new alleles
- Variation = raw material for evolution
- Low variation = population at risk
At the start of this lesson you were asked about the brown-eyed parents and their blue-eyed child, a puzzle that seemed impossible to explain. Now that you know about alleles, dominant and recessive traits, and how each parent passes on only half of their genetic information, go back to that question.
How does your new understanding of genes, alleles and heredity change the way you would answer it? Write a fuller explanation, and note anything that surprised you about how traits are actually inherited.
Q1. Define genetics and explain why it is an important area of scientific study. In your answer, refer to both heredity and variation. 3 MARKS
Q2. Distinguish between a gene, an allele and a chromosome . Use an example involving eye colour to illustrate your answer. 4 MARKS
Q3. 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
Revisit Your Initial Thinking
Go back to your Think First responses at the top of the lesson.
- Did you correctly identify that similarities between family members are due to shared genes/alleles passed from parents?
- Did you recognise that differences arise because each offspring receives a unique combination of alleles?
- Write one sentence summarising the most important new concept you learned about how genetic information is organised.
Model answers (click to reveal)
Comprehensive Answers
▼Activity 1, Inherited or Acquired?
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.
Activity 2, Family Trait Survey
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].
Multiple Choice
1. BHeredity is the passing of traits from parents to offspring. Option A defines variation. Option C defines mutation. Option D defines adaptation/evolution.
2. CChromosomes 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. ASiblings 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. DSelective 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. BVariation 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.
Short Answer Model Answers
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].
Jump Through Genetics!
Climb platforms using your knowledge of DNA, genes, chromosomes and alleles. Pool: Lesson 1.