Unit 4: Heredity and continuity of life

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).

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.

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.

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.

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.

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.

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.

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.