Question

determine how phenotypes can reappear after being eliminated from a population
the graphs above show a change in distribution of beak phenotypes 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.

Explanation:

• Option 1: Recessive genes can remain hidden (not expressed as a phenotype) when dominant genes are present. If the alleles for Beak X were recessive, they could be carried in the population without being visible (as a phenotype) in Generation 5. Then, in Generation 10, if two carriers (heterozygous individuals) mated and passed on the recessive alleles to their offspring, the Beak X phenotype could reappear. This is in line with Mendelian genetics.
• Option 2: While mutations can occur, beak - shape is a complex trait that is not likely to be mutated in a single - generation response to the environment in such a precise way to bring back a previously eliminated phenotype. Mutations are random changes in DNA, and for a specific beak shape (a complex morphological trait) to reappear due to mutation in one generation is highly unlikely.
• Option 3: Genetic mutation is not so frequent that a specific, complex phenotype (Beak X) would randomly reappear in a predictable generation (Generation 10). Mutations are random events, and the chance of getting the exact set of mutations to recreate Beak X in a specific generation is extremely low.
• Option 4: This is incorrect because of the possibility of recessive genes (as explained in Option 1). Extinction of a phenotype does not mean extinction of the underlying genes if they are recessive.

Answer:

Yes, the alleles for Beak X could remain in the population as a recessive gene.