Unit 4: Heredity and continuity of life
8 dot points across 3 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.
Topic 3: Continuity of life on Earth
- Describe key biotechnology techniques including PCR, gel electrophoresis, recombinant DNA technology, transgenic organisms (GMOs) and CRISPR-Cas9, and evaluate their applications
A focused answer to the QCE Biology Unit 4 dot point on biotechnology. Covers PCR (denaturation, annealing, extension, Taq, primers), gel electrophoresis (charge, size, ladder), recombinant DNA (restriction enzymes, plasmids, ligase, transformation), transgenic organisms (Bt cotton, golden rice, recombinant insulin) and CRISPR-Cas9 (guide RNA, PAM, repair pathways).
12 min answer → - Explain natural selection as a mechanism of evolution including variation, selection pressure, differential survival and reproduction, fitness, and compare Darwinian and neo-Darwinian theories
A focused answer to the QCE Biology Unit 4 dot point on natural selection. Covers the four preconditions (variation, heritability, differential survival and reproduction), defines fitness as reproductive success, distinguishes Darwin's theory from the neo-Darwinian synthesis (Mendelian genetics, mutation, population genetics) with examples in peppered moths, bacteria and cane toads.
11 min answer →
Topic 1: DNA, genes and the continuity of life
- Describe the structure of DNA, the process of semi-conservative replication and the role of key enzymes including helicase, DNA polymerase, primase and ligase
A focused answer to the QCE Biology Unit 4 dot point on DNA. Walks through the double-helix structure (sugar, phosphate, four bases, complementary pairing, antiparallel strands), the semi-conservative model demonstrated by Meselson and Stahl, and the roles of helicase, primase, DNA polymerase III, DNA polymerase I and ligase on the leading and lagging strands.
10 min answer → - Explain gene expression through transcription and translation, including the role of mRNA, tRNA, rRNA, the codon table and ribosomes, and compare prokaryotic and eukaryotic gene expression
A focused answer to the QCE Biology Unit 4 dot point on gene expression. Covers transcription (RNA polymerase, template strand, mRNA), the codon to amino acid code (universal, degenerate, non-overlapping), translation at the ribosome (initiation, elongation, termination) and the main differences between prokaryotic and eukaryotic expression.
11 min answer → - Describe types of mutation (point, frameshift, chromosomal) and the sources of genetic variation including meiosis, fertilisation and mutation, and explain the consequences of mutations for phenotype and population polymorphism
A focused answer to the QCE Biology Unit 4 dot point on mutations and variation. Covers point mutations (silent, missense, nonsense), frameshift indels, chromosomal mutations (deletion, duplication, inversion, translocation, non-disjunction) and the three sources of variation (independent assortment, crossing over, random fertilisation) plus mutation as the ultimate source.
10 min answer →
Topic 2: Inheritance
- Apply Mendel's laws of segregation and independent assortment to predict the outcomes of monohybrid and dihybrid crosses using Punnett squares, and explain the purpose of a test cross
A focused answer to the QCE Biology Unit 4 dot point on Mendelian genetics. Defines genotype, phenotype, allele, homozygous and heterozygous, applies the laws of segregation and independent assortment to monohybrid and dihybrid Punnett squares (3:1 and 9:3:3:1 ratios), and explains how a test cross with a homozygous recessive parent reveals the genotype of an unknown dominant phenotype.
9 min answer → - Describe and apply non-Mendelian patterns of inheritance including codominance, incomplete dominance, multiple alleles, sex linkage and polygenic inheritance
A focused answer to the QCE Biology Unit 4 dot point on non-Mendelian inheritance. Walks through codominance (ABO blood groups, roan cattle), incomplete dominance (snapdragon flower colour), multiple alleles (ABO, coat colour), X-linked inheritance (haemophilia, colour blindness, Punnett squares with sex chromosomes), and polygenic inheritance (skin colour, height) with continuous variation.
10 min answer → - Interpret pedigrees to deduce patterns of inheritance (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive) and calculate the probability of specified offspring genotypes and phenotypes
A focused answer to the QCE Biology Unit 4 dot point on pedigree analysis. Explains pedigree symbols, generation and individual numbering, the four inheritance patterns and the signature clues for each (skipped generations, sex bias, affected fathers and daughters), and works through probability calculations using the product and sum rules for combined events.
9 min answer →