A geneticist crossed tall pea plants and obtained 971 tall pea plants and 315 short pea plants in the F1 generation. A Punnett square for tall and short pea plants is shown.

What were the genotypes of the parents that produced the offspring in the Punnett square shown, if T is the allele for tall, and t is the allele for short?
A. Tt
B. TT
C. tt
D.

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?