What are the differences between conventional pcr andreal time pcr?

PCR allows amplification of DNA for a specific gene, after too many cycles of PCR the result will reach saturation, basically meaning all of the DNA has been amplified.

Conventional PCR will basically tell you whether or not a gene is expressed in your sample. This can be done semi-quantitavely if the PCR is performed for a low number of cycles, ie it will tell you whether one sample expresses more of your gene of interest than another sample. The results are seen by separating the PCR products by agarose gel/ethidium bromide electrophoresis.

Real-time PCR will record exactly what cycle of PCR a detectable level of amplified product became detectable, giving a far more accurately quantifiable estimation of gene expression.