WACE Biology · Unit 3
WACE Biology Unit 3: Heredity & Continuity of Species — Flashcards & Quiz
WACE Biology Unit 3 explores heredity and the continuity of species — how genetic information is stored, copied and passed from one generation to the next. These free flashcards and true/false questions cover DNA structure and replication, the cell cycle, mitosis and meiosis, Mendelian genetics including Punnett squares, incomplete dominance, codominance, sex-linked inheritance, pedigree analysis, karyotypes and chromosomal abnormalities. Every card is aligned to the SCSA Biology ATAR syllabus so you study exactly what appears in your WACE external examination. Master these foundational genetics concepts with spaced repetition — the most effective study technique for locking knowledge into long-term memory before your WA exam.
Key Terms
- Semi-Conservative Replication
- The SCSA-prescribed model of DNA copying in which each new double-stranded molecule retains one original parent strand and one newly synthesised strand, as assessed in the WACE ATAR course exam Unit 3 Heredity module.
- Allele
- An alternative form of a gene occupying the same locus on homologous chromosomes. In the SCSA Unit 3 curriculum, students must distinguish between dominant, recessive, and codominant alleles when completing genetic crosses.
- Meiosis
- A two-stage cell division process producing four genetically unique haploid gametes. The WACE Biology ATAR course requires students to explain how crossing over and independent assortment during meiosis generate genetic variation.
- Punnett Square
- A grid-based tool used in WACE ATAR exam responses to predict genotypic and phenotypic ratios from parental crosses, including monohybrid, dihybrid and sex-linked scenarios as specified by SCSA.
- Non-Disjunction
- The failure of chromosomes to separate correctly during meiosis, producing aneuploid gametes. SCSA expects Western Australian students to link non-disjunction to conditions such as trisomy 21 and Turner syndrome.
- Codominance
- An inheritance pattern where both alleles in a heterozygote are fully and simultaneously expressed, producing a phenotype distinct from blending. The WACE ATAR course exam distinguishes this from incomplete dominance.
- Karyotype
- An organised display of an organism's chromosomes arranged by size and centromere position. SCSA assesses the ability to interpret karyotype images to identify chromosomal abnormalities in Unit 3 exam questions.
Sample Flashcards
Q1: Describe the structure of a DNA nucleotide.
A DNA nucleotide consists of three components: a deoxyribose sugar, a phosphate group and one of four nitrogenous bases — adenine (A), thymine (T), guanine (G) or cytosine (C). Nucleotides are joined by phosphodiester bonds to form a polynucleotide strand.
Q2: Explain complementary base pairing in DNA.
In DNA, adenine (A) always pairs with thymine (T) via two hydrogen bonds, and guanine (G) always pairs with cytosine (C) via three hydrogen bonds. This ensures the two antiparallel strands are complementary.
Q3: Outline the steps of semi-conservative DNA replication.
1) Helicase unwinds and unzips the double helix by breaking hydrogen bonds. 2) Each strand acts as a template. 3) DNA polymerase adds complementary nucleotides in the 5' to 3' direction. 4) The leading strand is synthesised continuously; the lagging strand is synthesised in Okazaki fragments. 5) DNA ligase joins the fragments, producing two identical DNA molecules.
Q4: Describe the stages of the cell cycle.
The cell cycle consists of interphase (G₁ — cell growth; S — DNA replication; G₂ — preparation for division) and the mitotic phase (mitosis + cytokinesis). Most of the cycle is spent in interphase.
Q5: What is the purpose of mitosis and what are its stages?
Mitosis produces two genetically identical daughter cells for growth, repair and asexual reproduction. Stages: Prophase (chromosomes condense, spindle forms), Metaphase (chromosomes align at the equator), Anaphase (sister chromatids separate to poles), Telophase (nuclear envelopes reform, chromosomes decondense). Cytokinesis divides the cytoplasm.
Q6: How does meiosis differ from mitosis?
Meiosis involves two rounds of division (meiosis I and II), producing four genetically unique haploid cells (gametes). Key differences: homologous chromosomes pair up and cross over in prophase I; homologues separate in anaphase I (reductional division); sister chromatids separate in anaphase II. Mitosis produces two identical diploid cells.
Q7: Explain how crossing over and independent assortment generate genetic variation.
Crossing over: during prophase I, homologous chromosomes exchange segments of DNA at chiasmata, creating recombinant chromatids. Independent assortment: during metaphase I, homologous pairs orient randomly at the equator, so each gamete receives a random mix of maternal and paternal chromosomes. Together, these produce enormous genetic diversity in offspring.
Q8: State Mendel's Law of Segregation.
The Law of Segregation states that during gamete formation, the two alleles for each gene separate (segregate) so that each gamete carries only one allele for each trait. At fertilisation, offspring receive one allele from each parent.
Sample Quiz Questions
Q1: A DNA nucleotide consists of a ribose sugar, a phosphate group and a nitrogenous base.
Answer: FALSE
DNA nucleotides contain deoxyribose sugar, not ribose. Ribose is found in RNA nucleotides.
Q2: In DNA, guanine pairs with cytosine via three hydrogen bonds.
Answer: TRUE
Guanine (G) always pairs with cytosine (C) through three hydrogen bonds, while adenine (A) pairs with thymine (T) through two hydrogen bonds.
Q3: DNA replication is described as semi-conservative because each new molecule contains one original strand and one new strand.
Answer: TRUE
Semi-conservative replication means each daughter DNA molecule retains (conserves) one parental strand and has one newly synthesised strand, as demonstrated by Meselson and Stahl.
Q4: DNA polymerase unwinds the double helix during replication.
Answer: FALSE
Helicase unwinds and unzips the double helix by breaking hydrogen bonds. DNA polymerase adds complementary nucleotides to the template strand.
Q5: Cells spend most of their time in the mitotic phase of the cell cycle.
Answer: FALSE
Cells spend the majority of their time in interphase (G₁, S and G₂ phases), which involves growth, DNA replication and preparation for division. The mitotic phase is relatively brief.
Why It Matters
Heredity forms the foundation of modern biology, connecting molecular genetics to observable traits. For WACE Biology students, understanding how DNA encodes information, how genes are transmitted across generations, and how Mendelian principles predict inheritance patterns is essential. This topic frequently appears in exam questions requiring you to interpret pedigrees, complete Punnett squares, and explain deviations from expected ratios. Mastering genetic crosses, including dihybrid and sex-linked inheritance, builds analytical skills that extend into gene regulation and evolution topics. This module connects directly to Unit 4 evolution content, where understanding allele frequencies and inheritance underpins population genetics. Exam questions on heredity commonly appear in the extended response section, so practise linking Punnett square results to real phenotypic ratios. Strong performance here often distinguishes high-achieving students in the external exam.
Key Concepts
DNA Structure and Replication
Understanding the double helix, complementary base pairing, and semi-conservative replication is critical. You need to explain how DNA faithfully copies itself before cell division, the role of enzymes like helicase and DNA polymerase, and why accuracy matters for passing genetic information to daughter cells.
Mendelian Genetics and Genetic Crosses
Gregor Mendel's laws of segregation and independent assortment explain how alleles separate during gamete formation. Practise completing monohybrid and dihybrid Punnett squares, calculating phenotypic and genotypic ratios, and recognising patterns like co-dominance, incomplete dominance, and multiple alleles.
Sex-Linked and Non-Mendelian Inheritance
Genes on the X chromosome follow distinct inheritance patterns, producing different ratios in males and females. Study sex-linked conditions like haemophilia, and understand how epistasis, polygenic inheritance, and environmental influences cause traits to deviate from simple Mendelian predictions.
Pedigree Analysis
Pedigree diagrams are a staple of WACE Biology exams. Learn to identify autosomal versus sex-linked inheritance, determine whether traits are dominant or recessive, and calculate the probability of offspring inheriting specific genotypes by tracing alleles through multiple generations.
Common Mistakes to Avoid
- Confusing codominance with incomplete dominance on WACE ATAR exam responses — codominance shows both phenotypes simultaneously while incomplete dominance produces a blended intermediate; SCSA marking guides penalise conflation of these terms.
- Stating that non-disjunction only occurs in meiosis I — the SCSA Unit 3 course requires students to recognise it can occur in meiosis II as well, producing different gamete abnormalities.
- Using uppercase and lowercase letters for codominant alleles instead of the superscript notation required by SCSA — WACE examiners expect notation like C^R C^W rather than simple Rr for codominance.
- Forgetting to include the location dependency in useEffect when studying — in a WACE ATAR exam context, students often omit that crossing over occurs specifically during prophase I, not prophase II.
- Failing to state both genotypic and phenotypic ratios when completing Punnett squares — SCSA WACE marking guides typically allocate separate marks for each ratio.
Study Tips
- Practise drawing Punnett squares under timed conditions until you can complete dihybrid crosses in under three minutes without errors.
- Create flashcards pairing each inheritance pattern with a worked example, and review them using spaced repetition to lock in the logic.
- Work through past WACE exam pedigree questions and annotate each individual's possible genotype before checking the marking key.
- Summarise the differences between co-dominance, incomplete dominance, and multiple alleles in a comparison table for quick revision.
- Teach a study partner how to solve a genetic cross problem — explaining the reasoning out loud reveals gaps in your understanding.
- Before your exam, work through the practice questions in this set at least twice using spaced repetition. Testing yourself repeatedly is the most effective revision strategy for long-term retention.
Related Topics
Frequently Asked Questions
What does WACE Biology Unit 3 Heredity cover?
Unit 3 Heredity covers DNA structure and replication, the cell cycle (interphase, mitosis, cytokinesis), meiosis and genetic variation, Mendelian inheritance including monohybrid and dihybrid crosses, codominance, incomplete dominance, sex-linked traits, pedigree analysis, karyotypes and chromosomal abnormalities such as Down syndrome.
How many flashcards are in this set?
This free set contains 20 flashcards and 20 true/false quiz questions covering all key concepts in WACE Biology Unit 3 Heredity, aligned to the SCSA Biology ATAR course.
Are these flashcards aligned to the SCSA WACE syllabus?
Yes — every flashcard and quiz question is mapped to the SCSA Biology ATAR Unit 3 syllabus content for Heredity and Continuity of Species, ensuring relevance to your WACE external examination.
Last updated: March 2026 · 20 flashcards · 20 quiz questions · Content aligned to the SCSA Curriculum