What is dopamine? What role does it play in the brain

Which would be the outcome in a fertilized egg if the process of meiosis did not occur? twice as many chromosomes as the parents half as many chromosomes as the parents same number of chromosomes as the parents triple the number of chromosomes as the parents?

Restriction enzymes are used in making recombinant dna. describe the role restriction enzymes perform when constructing recombinant dna.

Ialready know the answers to these questions and they are on the attachment. but i just need to know why that answer is the correct one. plz asap! this is for a report that i need to email by 10!