How do a chromosome, a gene, and an allele differ? How are they similar?

A gene is a sequence of nucleotides in DNA or RNA that encodes the synthesis of a gene product, either RNA or protein. A chromosome is a long DNA molecule with part or all of the genetic material of an organism. A allele is one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Explanation:

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.