Practise A2 genetic technology by explaining gene-transfer choices, PCR and gel results, and how fluorescent probes or sequence databases reveal genetic information.
The potato plant, Solanum tuberosum, is an important food crop. Crop yield is reduced if the leaves of the plant are eaten by the larvae (immature stages) of the Colorado beetle, Leptinotarsa decemlineata.
Crop scientists used recombinant DNA technology to create two genetically modified (GM) varieties of potato plant. These plants produce proteins that are poisonous to insects.
- GM potato variety A contains two new genes, S N and Bt.
- GM potato variety B contains two new genes, SN and OCII.
The new varieties were tested by having a constant number of Colorado beetle larvae introduced to the plants at time 0 hours. The number of larvae that were alive after 24,48 and 72 hours was recorded. The percentage of the larvae that had died in each time interval was calculated. This was repeated for potato plants that had not been genetically modified (non-GM).
Table 4.1 shows the percentage of Colorado beetle larvae that had died on the GM potato plant varieties and on non-GM potato plants.
Table 4.1
Suggest what is meant by recombinant DNA technology.
Adenosine deaminase (ADA) deficiency is an immune system disorder caused by a recessive autosomal mutation.
Severe combined immunodeficiency caused by a lack of ADA is called ADA-SCID.
Genetic engineering is used to make a recombinant human protein to treat people with ADA-SCID.
Outline the principles of genetic engineering.
In 2016 gene therapy to cure ADA-SCID was approved in Europe. The gene therapy involves three main steps.
- Blood (haematopoietic) stem cells are taken from the bone marrow of the person with ADA-SCID.
- The functional gene and its promoter are inserted into the blood stem cells.
- A single infusion (injection) of the gene-corrected cells is given to the patient.
Explain why a promoter has to be transferred as well as the desired gene.
The gene therapy technique used to cure ADA-SCID is not suitable for treating the genetic disease called Huntington's disease. A newer technique called gene editing could potentially be used instead to cure Huntington's disease.
Explain why gene editing is more suitable as a potential cure for Huntington's disease.
Factor VIII can be made as a recombinant human protein.
The gene that codes for human factor VIII can be synthesised from messenger RNA purified from human liver cells.
Name the enzyme that uses messenger RNA as a template to produce complementary DNA.
Outline two sources, other than messenger RNA, from which genes can be obtained for genetic engineering.
The gene that codes for human factor VIII can be transferred into mammalian cells in tissue culture.
Explain why a promoter also needs to be transferred into the mammalian cells so that human factor VIII can be synthesised.