Think about Gregor Mendel growing generation upon generation of pea plants, trying to find
out why some plants produced certain traits
while others didn't.
Think about how hard it can be just to keep
plants alive!
If you were like Mendel and trying to design
experiments with pea plants, what would you
need to think about in your planning in order
to get good results?

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?