A) Although in some cases researchers have inferred that gene families are adaptive, gene families may also evolve due to genetic drift.
B) Having multiple copies of a gene can increase transcription and translation of the gene, so when increased transcription is adaptive, then natural selection favors genes duplicating into gene families.
C) Gene families are adaptive because each gene can produce a slightly different protein, which allows for diverse functions that are favored by natural selection.
D) Gene families evolve because of the activity of mobile genetic elements, which cause repeated gene duplication events.

A) Multicellular eukaryote genomes have a greater number of protein-coding genes than prokaryote genomes.
B) Prokaryote genomes have more introns than multicellular eukaryote genomes.
C) Multicellular eukaryote genomes have larger intergenic regions than prokaryote genomes.
D) There are more mobile genetic elements in prokaryote genomes than in multicellular eukaryote genomes.

A) natural selection only
B) genetic drift only
C) both natural selection and genetic drift, acting in the same direction to either increase or decrease mutation rates
D) both natural selection and genetic drift, acting in opposing directions: one process favors increasing mutation rates and the other favors decreasing mutation rates