In your garden, you are growing several plants of the species florus imaginarium. you have observed that some of the individuals have leaves with rounded tips and others have leaves with pointed tips. one of these traits is dominant and the other is recessive. assuming all the plants in your garden are true-breeding, how would you go about determining which trait is dominant and recessive?

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?