How can we explain this change in terms of allelic frequency

Population genetics describes the genetic composition of a population, including allele frequencies, and how allele frequencies are expected to change over time. ... In natural populations natural selection (adaptation mechanism), gene flow, and mutation combine to change allele frequencies across generations      

Explanation:

maritime tropical may be your answer.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.