A person who has a weakened immune system may not be able to fight against infection because pathogens may enter the body and cause illness.
phagocytes may enter the body and cause illness.
normal cells crowd out unhealthy cells.
antibodies production is increased.

All individuals have two alleles for a given trait. according to mendel's these alleles are passed down one each from both mother and father.

Explain the process that creates the heat of the sun?

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?