IGCSE Biology / Selective breeding
Transgenic organisms and using cloned animals to make human proteins revision notes
Edexcel International GCSE Biology (4BI1), chapter 20: Selective breeding, specification point 5.16, 5.20B. Free lesson.
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A transgenic organism has genetic material transferred from a different species. A transgenic animal can make a human protein in its milk, then be cloned so that many genetically identical animals make the same protein.
What makes an organism transgenic?
An organism is transgenic when genetic material has moved from one species into another. The key test is whether the gene crossed a species boundary. This is different from selective breeding, which selects parents with useful characteristics but does not transfer a gene from another species. Bacteria with the human insulin gene: transgenic, because a human gene is in a bacterium. Maize with a bacterial insecticide gene: transgenic, because the gene crossed from a bacterium to a plant. A sheep with a human gene in its milk: transgenic, because a human gene is in a sheep. A cow bred…
How a sheep is made to produce a human protein
A human gene for a wanted protein, such as a blood-clotting factor, is put into a sheep so the protein is made in its milk. A promoter is a DNA sequence that switches a gene on. Using one that works in milk-producing cells means the protein is made in milk, where it can be collected and purified.
Why clone the successful animal?
Making a transgenic animal takes many attempts, and most attempts fail. It would be impractical to repeat the whole process for every animal. Instead, the one successful animal is cloned. Cloning transfers a diploid nucleus from one of its body cells into an enucleated egg cell, an egg cell with its nucleus removed. Dolly the sheep is an example of this method. Clones are genetically identical to the successful animal, so each carries the inserted gene. Each clone can produce the same human protein in its milk.
Why not breed the animal normally?
Sexual reproduction produces variation in the offspring. They receive different combinations of alleles, so not every offspring will inherit the inserted gene, and those that do may produce different amounts of protein. Cloning gives a reliable group of animals with the same genetic make-up as the successful animal.