The graphs above show a change in distribution of beak phenotyzes x, y, and z over 10 generations. notice that beak x completely disappears from the population by generation 5, but reappears by generation 10. could this occur in nature? how? yes, the alleles for beak x could remain in the population as a recessive gene. yes, the birds could mutate their beaks in response to a change in the environment. yes, genetic mutation is so frequent that beak x will likely reappear randomly by generation 10. no, once birds with beak x are extinct, they cannot appear again.