CCEA A Level Biology 5.4 Gene Technology Exam Questions

About CCEA A Level Biology 5.4 Gene Technology

Gene technology, section 5.4 of Unit A2 2, is one of the most detailed parts of the CCEA course. You need PCR, DNA probes, genetic markers (microsatellite repeat sequences and SNPs), microarrays, genetic fingerprinting with restriction enzymes and gel electrophoresis, and the stages of gene transfer into bacteria or yeast using plasmids and phages with marker genes. Applications include GM microorganisms, transgenic animals and plants, gene therapy (with haemophilia B and cystic fibrosis as examples), genome sequencing, knockout and knockin mice, and pharmacogenetics and personalised medicine. You must also discuss ethical, social, legal and ecological issues. Gel electrophoresis or DNA extraction is the linked practical.

What you need to know

• PCR Cycles of heating to about 95 C to separate strands, cooling so primers anneal, and heating to about 72 C so heat-stable DNA polymerase extends them. Each cycle doubles the DNA.
• Probes, markers and microarrays A DNA probe is a short labelled single strand that binds a complementary sequence. Microsatellite repeat sequences and SNPs vary between individuals. A microarray has thousands of probes on a chip; fluorescent sample DNA binds and signal strength shows sequence variation or expression level.
• Genetic fingerprinting Restriction endonucleases cut DNA at specific sites; gel electrophoresis separates fragments by size as DNA (negatively charged) moves towards the anode; probes locate specific fragments.
• Gene transfer Obtain the gene with restriction endonucleases or make it from mRNA using reverse transcriptase; insert it into a vector (plasmid or phage) using the same restriction enzyme and ligase; transform E. coli or yeast; identify transformed cells with marker genes such as antibiotic resistance or fluorescence; then grow them on a large scale.
• Applications Transgenic plants give higher yields and pest resistance; transgenic animals can produce pharmaceutical proteins. Gene therapy adds working copies of genes to somatic cells (not passed on) or germ line cells (passed on); haemophilia B has been treated successfully, while cystic fibrosis needs repeated treatment.
• Sequencing and pharmacogenetics The Human Genome Project sequenced about 3 billion nucleotides and around 21 000 genes. Knockout mice show gene function. Pharmacogenetics uses a person's genotype to predict drug response, for example to codeine, enabling personalised medicine.
• Issues and safety Concerns include gene flow to wild species, effects on ecosystems, ownership of genetic data and germ line changes. Safety measures include using ill-adapted bacterial strains, suicide genes and containment.

Common mistakes in 5.4 Gene Technology

• Saying DNA moves to the negative electrode in electrophoresis. DNA is negatively charged so moves towards the positive electrode, with smaller fragments moving further.
• Saying PCR uses normal DNA polymerase. It needs a heat-stable polymerase such as Taq that is not denatured at 95 C.
• Forgetting to use the same restriction enzyme for gene and vector. The same enzyme produces complementary sticky ends so they can be joined by ligase.
• Saying somatic gene therapy is inherited. Only germ line therapy affects offspring.
• Giving ethical points with no explanation. Explain the specific benefit or risk, for example insect-resistant crops reducing pesticide use.

Try three 5.4 Gene Technology exam-style questions