What is the only new source of genes in an organism?

Answer 1

There are many sources of new genes, and mutations are not necessarily at the top of the list. Whoever asked the question is probably being overly simplistic and is looking for mutations as the answer.

Depending on the organism there are plenty of means of horizontal gene transfer (transfer from one organsim to another) that don't involve mutation, including but not limited to viruses, transposable elements, conjugation, plasmids and transformation.

Answer 2

There is more than one source. Mutation is the obvious answer, but what about recombinant DNA in biotechnology and genetic engineering? Because the genes are changed, the DNA of an organism can be used to form proteins not normally produced in a cell, to produce drugs or vaccines, or promote human health. Bacteria that carry recombinant DNA can increase soil fertility, serve as insecticides, or relieve pollution. None of this would happen with just mutation being the source of new genes.

Answer 3

Mutations

Answer 4

In addition to mutations, you have crossover.
Crossover isn't considered a mutation by most textbooks.

The context of the question will change the appropriate answer.

Answer 5

mutation
mutations happen spontaneously or as a result of errors in replication.
Mutations are kept around by natural selection (they provide a new function or capability that aides in adaption) or speciation (they delineate a new sub-species or species)

Answer 6

Also viruses can integrate into the genome.