Coaching Centre
Genetics and biotechnology review
A summary of the whole Genetics and Biotechnology chapter, key words, and a mixed test covering DNA, chromosomes, meiosis, protein synthesis, mutations, inheritance patterns, pedigrees, PCR and profiling, genetic engineering, CRISPR and ethics.
Use this page to check the whole chapter. Read the summary, make sure you can explain every key word, then do the test without looking back.
Chapter summary
| Topic | What you need to know |
|---|---|
| 1A Structure of DNA | Miescher (1869), Levene (nucleotides), Avery and Hershey–Chase (DNA is genetic material), Chargaff (A = T, G = C), Franklin and Gosling (Photo 51, 1952), Watson and Crick (double helix, 1953). Nucleotide = phosphate + deoxyribose + base. Antiparallel strands; A–T (2 H-bonds), G–C (3). Semi-conservative replication by helicase and DNA polymerase. DNA extraction. |
| 1B Genes, chromosomes, genomes | DNA wraps round histones → chromatin → chromosomes (two sister chromatids, centromere). Gene, locus, allele. Homologous pairs; diploid 2n, haploid n; 22 pairs of autosomes + XX or XY. Karyotypes; trisomy 21, XXY, 45,X. Chromosome number varies (jack jumper ant 2, human 46, dog 78). Genome 3.1 billion bp, ~20 000 genes, 1–2% coding; HGP 2003, complete T2T genome 2022; mitochondrial DNA from mother. |
| 1C Meiosis and variation | Mitosis: 2 identical diploid cells. Meiosis: 4 different haploid cells, number halves in meiosis I. Variation: independent assortment (223), crossing over at chiasmata (recombinant chromosomes), random fertilisation. Linked genes; 1% recombination = 1 map unit (Sturtevant 1913). Nondisjunction → trisomy or monosomy. |
| 1D Gene to protein | DNA → mRNA → protein → trait. RNA: single strand, ribose, U instead of T. Transcription (nucleus, RNA polymerase, template strand); translation (ribosome, codons, tRNA anticodons, start AUG, stop codons). 64 codons, redundant, almost universal; cracked 1961–66. mRNA vaccines. |
| 1E Mutations | Spontaneous or induced by mutagens (UV, X-rays, tobacco chemicals). Substitution, insertion, deletion → silent, missense, nonsense, frameshift. Sickle cell (GAG → GTG, Glu → Val; carriers resist malaria). Chromosome mutations: deletion, duplication, inversion, translocation. Somatic vs germline. CF F508del; CFTR modulators. |
| 1F Mendel and Punnett squares | Mendel's peas, P/F1/F2, 3 : 1. Dominant, recessive, genotype, phenotype, homozygous, heterozygous, carrier. Punnett squares; ratios are probabilities for each offspring. Test cross with homozygous recessive. Labradors B/b (and E/e epistasis). |
| 1G Beyond simple dominance | Incomplete dominance (pink snapdragons, 1 : 2 : 1); codominance (roan cattle). ABO: Iᴬ, Iᴮ codominant, i recessive; groups A, B, AB, O. Polygenic traits, continuous variation. Environment (hydrangeas, temperature and reptile sex, twins) and epigenetics. |
| 1H Sex linkage and pedigrees | Father's sperm decides sex. X-linked recessive (colour blindness, haemophilia): more males affected, carrier females, no father-to-son passing. Pedigree symbols. Unaffected parents → affected child = recessive; affected parents → unaffected child = dominant; father-to-son = not X-linked. |
| 1I PCR and DNA profiling | PCR (Mullis 1983): denature 95 °C, anneal ~55 °C, extend 72 °C with Taq; doubles each cycle. Restriction enzymes and sticky ends. Gel electrophoresis: DNA negative, moves to +, short fragments furthest. STR profiles (~20 sites) for forensics, paternity, remains, conservation; limits. |
| 1J Genetic engineering and CRISPR | Recombinant DNA: restriction enzyme, plasmid vector, ligase, transgenic bacteria (human insulin 1982). GM crops: Bt cotton (>99% of Australian crop), Golden Rice. Sanger sequencing (1977) → next-generation sequencing; bioinformatics, AlphaFold. CRISPR-Cas9 (2012): guide RNA, PAM, cut, knock-out or template repair. Gene therapy: Luxturna, Zolgensma, Casgevy (first CRISPR therapy, 2023). |
| 1K Testing and ethics | Newborn (PKU), carrier (Mackenzie's Mission; Medicare-funded since 2023), prenatal, diagnostic, predictive testing. iPS cells; Dolly (1996, somatic cell nuclear transfer). Approved GM foods as safe as conventional; debates on environment, economics, choice. Germline editing (He Jiankui 2018). Indigenous data sovereignty, CARE principles, NCIG. |
Putting it together
The chapter follows one molecule through every level of life. The sequence of bases in DNA stores information; base pairing lets it copy itself and be transcribed into mRNA, and the genetic code turns that into the sequence of amino acids in a protein, whose shape decides what it does, and so the characteristics we see. Mutations change the sequence and create new alleles. Meiosis and fertilisation shuffle those alleles into new combinations, and the rules of dominance, codominance and sex linkage let us predict what offspring will probably inherit, with the environment shaping how genes are expressed. Because the code is universal, the same tools that cells use (polymerases, restriction enzymes, ligases, Cas9) can be used by scientists to copy, read, cut and edit DNA in any organism. That power brings benefits in medicine, farming and justice, and questions about safety, consent, fairness and who controls genetic information.
Key words
allele · amino acid · anticodon · antiparallel · autosome · bioinformatics · carrier · Cas9 · centromere · Chargaff's rules · chiasma · chromatid · chromatin · chromosome · cloning · codominance · codon · complementary base pairing · CRISPR · crossing over · deletion · diploid · DNA · DNA ligase · DNA polymerase · DNA profile · dominant · double helix · epigenetics · F1 / F2 generation · frameshift · gel electrophoresis · gene · gene therapy · genome · genotype · germline mutation · guide RNA · haploid · helicase · heterozygous · histone · homologous chromosomes · homozygous · incomplete dominance · independent assortment · Indigenous data sovereignty · insertion · karyotype · linked genes · meiosis · missense · monohybrid cross · mRNA · multiple alleles · mutagen · mutation · nondisjunction · nonsense mutation · nucleotide · PAM · PCR · pedigree · phenotype · plasmid · polygenic · primer · protein synthesis · Punnett square · recessive · recombinant DNA · replication · restriction enzyme · ribosome · RNA · semi-conservative · sex-linked · short tandem repeat · silent mutation · somatic mutation · sticky ends · substitution · test cross · transcription · transgenic · translation · trisomy · tRNA · vector · X-linked
Test yourself
A DNA strand reads 5′ AGTC 3′. Its complementary strand reads
A–T, G–C, and the strands are antiparallel.
Which statement about meiosis is correct?
Meiosis I separates homologous pairs, halving the chromosome number.
The mRNA codon CAU is read on a ribosome. The tRNA anticodon that pairs with it is
C–G, A–U, U–A, and tRNA is RNA, so it uses U.
A deletion of three bases in a gene will most likely
Three bases = one codon, as in the F508del CF mutation.
In cats, a gene for coat length has alleles S (short, dominant) and s (long). Ss × ss gives
Ss, Ss, ss, ss.
A mother is group O and a child is group AB. This is
An AB child needs Iᴬ from one parent and Iᴮ from the other; a group O mother can only give i.
A haemophilia allele could pass from
Sons receive their X from their mother.
In PCR, primers are needed because
The primer gives the polymerase a starting point and marks the section to copy.
Cas9 will only cut DNA where
Both the match and the PAM are required.
Label CRISPR gene editing.
DNA, RNA or both?
Order the stages from gene to characteristic.
A permanent change in DNA is a . An organism with two different alleles for a gene is . A family tree showing a trait is a . In gel electrophoresis, the fragments travel furthest. A small loop of bacterial DNA used as a vector is a . Making genetically identical copies of an organism is .
Cystic fibrosis is an autosomal recessive condition caused by mutations in the CFTR gene. Using this example, explain how a change in DNA leads to a disease, how CF is inherited by children of two carriers, and evaluate two modern technologies that are used to diagnose, prevent or treat it.
The CFTR gene codes for a channel protein that moves chloride ions out of cells lining the lungs and gut; water follows, keeping mucus thin. In the common F508del mutation, three bases are deleted, so one amino acid (phenylalanine 508) is missing. The protein misfolds and is destroyed, so too little chloride and water leave the cells, and mucus becomes thick and sticky, blocking airways and the pancreas. Because the allele is recessive, carriers (Ff) are healthy. If two carriers have a child, a Punnett square gives FF, Ff, Ff and ff, so each pregnancy has a 1 in 4 chance of a child with CF and a 1 in 2 chance of a carrier. Carrier screening, now Medicare-funded in Australia, can identify couples who are both carriers before pregnancy. Its benefit is that couples can make informed choices, such as IVF with embryo testing; limitations are that it does not detect every rare mutation, and the choices can raise difficult ethical questions. CFTR modulator drugs such as Trikafta help the faulty protein fold and work. They have greatly improved lung function and life expectancy for people with at least one F508del allele, but they treat rather than cure the disease, must be taken for life, and are extremely expensive without government subsidy. By contrast, gene therapy for CF, once expected to cure it, has not yet worked well enough to be used.