Hi Abhishek
Mr Rama Chary has already explained a lot.
Following are my few bits:-
A property can be purchased under the joint names of your mother and your name with percentage share in proportion to the amounts paid by each joint holder. So the tax benefit would be proportionate to the amount paid by each joint holder.
To keep it crystal clear for future with tax authorities, you (Abhishek) can put in 1% or even less ( but not Zero) of the purchase price and rest of the amount by your mother. LTCG tax for your mother would be calculated accordingly (99% property purchase price), and you will need to explain ( if required) balance 1% paid by you to the tax people.
During filing of ITR, both would need to show in individual ITRs the property purchase along with TDS deduction from the seller ( as per percentage of the property share) and the share of the property in percentage. Tax would get calculated accordingly.
Finally, when one of the joint holders is no more in this world, the whole property would be vested automatically to the remaining joint holder. So no need for any gift deed etc, which would lead to re-registration with good amount of registration fee.
Regarding, changing of registration documents in such a case( the method explained by me), different states have different bye laws, some states allow registration change with just a tiny amount of a few thousand rupees. Other states may ask for a percentage of the market rate of the property at that time, which could be even 1%.
Hope I have been able to provide some useful info.