Question

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.

Answer 1

Best answer: Yes — the alleles for Beak X could remain in the population as a recessive gene.

Why:
- A recessive allele can be carried in heterozygotes without producing the X phenotype. If most carriers are heterozygous, the phenotype can disappear (no X/X individuals) but the allele still exists and can reappear when two carriers mate.
- Other realistic ways X could return: gene flow (immigration of birds carrying the allele) or, much less likely, a new mutation recreating the allele.

Why the other choices are wrong or misleading:
- “Birds could mutate their beaks in response to a change in the environment” implies directed (Lamarckian) change in individuals; that isn’t how genetic inheritance works. Some traits show plasticity, but beak phenotype reappearance across generations is explained genetically, not by individuals choosing or “mutating” their beaks.
- “Genetic mutation is so frequent that Beak X will likely reappear” overstates mutation rates. New mutations can produce similar phenotypes but are rare, so this is not the most likely explanation.
- “No, once extinct they cannot appear again” is false: the underlying allele can persist hidden, or be reintroduced by migration or mutation.