Hi,
For biasing a MOSFET with Drain and Gate connected through a resistor need a big resistor. Why we need to use big resistor? Will shorting Gate and Drain work for Biasing (still the current in feedback path is 0)?
Shorting Gate and Drain will bias the MOSFET into a "diode" connection, Vgs=Vds ; i.e. there will be no gain between input and output. With a high resistance between drain & gate you can have gain.
The gain depends on the operation point (transconductance), surrounding circuit elements' values and - last not least - generation impedance (input) and load impedance (output). Generally the MOSFET's gain in this circuit variant is much smaller than a BJT's gain, usually in the order of >1 ... 10 . See e.g. this example.