Asked by daniel
3 pie charts are shown. The first is labeled Generation 1 and has about 33 percent Beak X, 33 percent Beak Y, and 33 percent Beak Z. The second labeled Generation 5 has about 33 percent Beak Y and 66 percent Beak Z. The third labeled Generation 10 has 60 percent Beak Z, 30 percent Beak Y, and 10 percent Beak X.
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.
All Answers 1
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Best answer: Yes — the alleles for Beak X could remain in the population as a recessive gene.
Why:
- If the allele for Beak X is recessive, individuals can be heterozygous carriers (X allele hidden by a dominant allele). The X phenotype can disappear from view (no homozygous recessives) while the allele still exists in carriers. With the right matings (or changes in selection, drift, or migration), homozygous X individuals can reappear later.
- Migration (new birds carrying X entering the population) could also reintroduce the phenotype.
Why the other choices are wrong or unlikely:
- “Birds mutate their beaks in response to the environment” implies Lamarckian inheritance (acquired traits passed on). That is not how inherited genetic changes generally work, so this is not a valid explanation for a heritable trait reappearing.
- Random mutation could recreate the X allele, but spontaneous mutation rates are usually very low, so it’s unlikely to explain the quick reappearance by Generation 10 (possible but not the most plausible).
- “Once extinct they cannot appear again” is false because alleles can persist hidden in carriers or be reintroduced by migration or, rarely, mutation.
Why:
- If the allele for Beak X is recessive, individuals can be heterozygous carriers (X allele hidden by a dominant allele). The X phenotype can disappear from view (no homozygous recessives) while the allele still exists in carriers. With the right matings (or changes in selection, drift, or migration), homozygous X individuals can reappear later.
- Migration (new birds carrying X entering the population) could also reintroduce the phenotype.
Why the other choices are wrong or unlikely:
- “Birds mutate their beaks in response to the environment” implies Lamarckian inheritance (acquired traits passed on). That is not how inherited genetic changes generally work, so this is not a valid explanation for a heritable trait reappearing.
- Random mutation could recreate the X allele, but spontaneous mutation rates are usually very low, so it’s unlikely to explain the quick reappearance by Generation 10 (possible but not the most plausible).
- “Once extinct they cannot appear again” is false because alleles can persist hidden in carriers or be reintroduced by migration or, rarely, mutation.
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