Assertion: Transgenic mouse is termed a ‘super mouse’ because it is twice bigger in size than the normal mouse. Reason: In ‘super mouse’, the gene for human growth factor has been introduced and expressed. A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion. B. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion. C. Assertion is correct but Reason is incorrect. D. Both Assertion and Reason are incorrect.
Hint: A transgenic mouse or genetically engineered mouse model (GEMM) is a mouse whose genome has been altered through the use of genetic engineering techniques. These genetically modified mice are used in various researches and in oncology. Transgene is a gene that has been transferred naturally or by genetic engineering techniques from one organism to another.
Complete Answer: There are two basic technical approaches to produce transgenic mice. The first one is by means of pronuclear injection into a single cell of the mouse embryo. There it will randomly integrate into the mouse genome. This method creates a transgenic mouse and is used to insert new genetic information into the mouse genome or to over-express endogenous genes. The second approach involves modifying embryonic stem cells with a DNA construct containing DNA sequences homologous to the target gene. This method is used to manipulate a single gene, in most cases "knocking out" the target gene. Transgenic mice are individually termed as 'super mice' because they are twice as big in size than the normal mouse. For such mice to be studied for the purpose of various human medical researches, they have to be inserted with the human growth factor. Such factors also have been expressed and thereby enabled the study of obesity, heart disease, diabetes, arthritis, substance abuse, anxiety, aging, temperature and pain reception and Parkinson disease. Transgenic mice have also been generated to carry cloned oncogenes. Thus, transgene need not necessarily be a human growth factor gene; it could be artificial.
Therefore, option (B) Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion is the correct answer.
Note: The key difference between transgenic mouse and knockout mouse is that in latter the desired gene is inserted into a specific locus in the target genome via homologous recombination. By contrast, transgenic models use random integration, i.e., the desired gene could end up anywhere in the host genome.