How do cells in the ovary detect a hormone from
the brain?
(1) the brain sends a nerve impulse to the ovary.
(2) white blood cells bring the hormone to the
ovary.
(3) receptor molecules on the cells of the ovary
bind with the hormone.
(4) vacuoles within the ovary bind with the
hormone.

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?