Some organisms have a large geographic range. For example, the Norway rat lives on every
continent except Antarctica.
A population of Norway rats is the number of rats
in one particular area. Do you think it's
scientifically possible for a population of Norway
rats in North America to carry different genetic
mutations than a population of Norway rats in
Africa? Do you think it's possible that they carry
some of the same mutations? What types of
information can scientists learn by studying the
genomes of these two populations of rats?

Astudy by solloch and et. al., in 2017, gives the map above which shows the frequency of alleles with a ccr5-delta32 mutations over 87 different countries. this mutation deletes the presence of a co-receptor (ccr5) on the outside of human t-cells (lymphocytes). some viruses, such as the one responsible for the black death and human immunodeficiency virus (hiv), require this receptor for attachment to host cells during the infection process. the black death was an epidemic that passed over northern europe during the 14th century killing nearly 60% of europeans. according to this information, which explanation best explains why northern europeans show a greater immunity for hiv than some other parts of the world?