Explain the cre or lox system

Provided the rising rates of hypercholesterolemia and hypertension in the U.S. and other industrialized nations, you are interested in studying the importance of cholesterol transport in the sodium re-absorptive pathways in the kidney that are important for blood pressure control. One way to study this pathway is to use a mouse model in which an important transporter for cholesterol is “knocked out.”Standard gene targeting methods to “knock out” the cholesterol transporter, Abca1, create mice with several severe developmental abnormalities including glomerulonephritis, a kidney defect that would confound the study of other renal processes in this model. For this reason, you decided to make a tissue specific knockout mouse where Abca1 is only “knocked out” in your cell type of interest, the renal collecting duct principal cell. Luckily, you discover a commercially available, floxed Abca1 transgenic mouse model and a Cre-recombinase expressing mouse with the Cre gene downstream of the promoter for the water channel that is expressed in collecting duct principal cells (Aqp2).
Questions:
1) Describe the Cre/Lox system used to generate tissue-specific knockout mice.
2) Reading about the Aqp2-Cre mouse model, you discover that the Aqp2 promoter also causes Cre expression in the vas deferens and testes of male mice. Since these tissues also express Abca1, you desire to avoid mating Aqp2-Cre males as they are infertile. Design a breeding scheme (hint: use Punnett squares) that will produce Aqp2-Cre and floxed Abca1 mice without breeding Aqp2-Cre expressing male mice. (Remember the Cre recombinase gene only needs to be present on one chromosome to function.)
What are the ratios of different genotypes that this breeding scheme will produce?
3) In question 2 above, which genotypes would serve as your controls for future experiments? Why?

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