Any gene can be a reference gene if its Cq does not change (from sample to sample)in the face of treatment in the particular system studied. Assuming the exact same amount of nucleuc acid is loaded per reaction, the ideal reference gene (housekeeping gene) Cq should not deviate more than 0.2 or 0.3 Cq units per equally-loaded sample. Short question, short answer.
The answer above by Mr Gallup is theoretically perfect or this can be seen in ideal conditions. But in practical setup there is always a change in the gene expression (even for the house keeping gene) after treatment. That's why the concept of normalization is utilized in quantitative PCR experiments, where you can normalize the gene expression change in your target gene against the change in expression levels of housekeeping gene.
how you can normalize ur target gene with a housekeeping gene showing change in expression after treatment. Ideally we have to select a house keeping gene with less deviation as suggested by Jack M Gallup. Thanks for ur suggestions
that's right. that is what the concept of housekeeping genes say that it should not change expression but I am talking about practical situations where I always see some change in expression even in housekeeping genes. There is no ideal housekeeping gene which you can say with surety that it will have constant expression. The best thing would be start with a set of like 6 HKG and narrow down to the best one which have least change in expression.
it depends on the level of activation of cells, house keeping genes also varies. thats why we have to first choose the best house keeping gene (in a panel of atleast 10 HKG) showing no or little variation as suggested by Dr. Gallup. Thank you all for ur suggestions and comments
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