As difficult as learning quantum math
As difficult as running five miles in one minute
As difficult as learning three languages
As difficult as catching a greased pig
You need another comma after the word "think" because it's a parenthetical expression and is set off from the sentence.
The changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.