Question

how does speciation start to take place on a genetic level between two isolated populations?
allele frequencies change in different ways.
large numbers of mutations occur.
new genes are added to one group.
recessive alleles become dominant.

Explanation:

Speciation occurs when two populations become reproductively isolated. On a genetic level, this starts with changes in allele frequencies. Different selective pressures, genetic drift, etc., can cause allele frequencies in the two isolated populations to change in different ways. Over time, these differences can accumulate and lead to reproductive isolation. Mutations (while a source of genetic variation) don't necessarily start speciation in the way described in the options. Adding new genes to one group (gene flow is usually restricted in isolated populations). Recessive alleles becoming dominant is not the typical start of speciation at a genetic level between isolated populations.

Answer:

Allele frequencies change in different ways.