Given:
Aniket sold two Genesis for rupees 990 each.
On one Genesis, he gains 10%.
On the other Genesis, he loses 10%.

To Find:
The overall gain or loss percentage in the whole transaction.

Solution:
To find the overall gain or loss percentage, we need to calculate the total cost price (CP) and the total selling price (SP) of both Genesis.

Calculating CP and SP:
Let's assume the cost price of each Genesis is CP.

On the first Genesis, Aniket gains 10%.
So, the selling price (SP1) of the first Genesis can be calculated as:
SP1 = CP + (10/100) * CP
SP1 = CP + 0.1CP
SP1 = 1.1CP

On the second Genesis, Aniket loses 10%.
So, the selling price (SP2) of the second Genesis can be calculated as:
SP2 = CP - (10/100) * CP
SP2 = CP - 0.1CP
SP2 = 0.9CP

Aniket sold both the Genesis for rupees 990 each.
Therefore,
SP1 = 990
SP2 = 990

Now, we can equate the selling prices to find the value of CP:
1.1CP = 990 (from SP1)
0.9CP = 990 (from SP2)

Calculating CP:
Let's solve the equations to find the value of CP:
1.1CP = 990
CP = 990 / 1.1
CP = 900

0.9CP = 990
CP = 990 / 0.9
CP = 1100

From the above calculations, we can see that there is a contradiction in the values of CP. This suggests that there might be an error in the given information or the solution is not possible.

Conclusion:
Since we obtained contradictory values for the cost price (CP) of the Genesis, it is not possible to determine the overall gain or loss percentage in this transaction. It is advisable to recheck the given information or seek clarification to find a valid solution.