When you list things such as X, Y, and Z...can it be also grammatical correct to list it as X and Y and Z in a sentence or is this construction wrong?

thank you.

If you are composing a list, you should separate the elements of the list with commas and include "and" only before the final item in the list.

(You're also allowed to use semicolons instead of commas when the members of the list are especially long and/or and contain commas themselves. Not an issue I've seen on the GMAT.)

Rey