ðə "klˈæsɪk sᵻlˈɛktɪv swˈiːp" ɔːɹ "hˈɑːɹd sᵻlˈɛktɪv swˈiːp" ɪz ɛkspˈɛktᵻd tʊ əkˈɜː wɛn bˌɛnɪfˈɪʃəl mjuːtˈeɪʃənz ɑːɹ ɹˈɛɹ, bˌʌt wˈʌns ɐ bˌɛnɪfˈɪʃəl mjuːtˈeɪʃən hɐz əkˈɜːd ɪɾ ɪŋkɹˈiːsᵻz ɪn fɹˈiːkwənsi ɹˈæpɪdli, ðɛɹbˈaɪ dɹˈæstɪkli ɹᵻdˈuːsɪŋ dʒɪnˈɛɾɪk vˌɛɹɪˈeɪʃən ɪnðə pˌɑːpjʊlˈeɪʃən.
The "classic selective sweep" or "hard selective sweep" is expected to occur when beneficial mutations are rare, but once a beneficial mutation has occurred it increases in frequency rapidly, thereby drastically reducing genetic variation in the population.