Your sister-in-law never gets sick, while her male neighbour seems to be sick all the time. Although there are several explanations for this, one is that they are genetically different. Which of the following hypotheses concerning genetic inheritance of major histocompatibility complex (MHC) is consistent with this observation and your understanding of the immune system as described in the text?
A) MHC inheritance works like normal Mendelian genetics in the sense that there are dominant traits and recessive traits, and in the case of MHC, those with the dominant trait (including both those who are heterozygous and homozygous dominant) produce more normal MHC proteins and are healthier than those with the recessive trait (homozygous recessive).
B) In the case of MHC, it is beneficial to have as many different alleles as possible, so heterozygous individuals are healthier than homozygous dominant or recessive individuals.
C) MHC proteins are often closely associated with small antigen particles that have been broken off the main pathogen, so that individuals who are recessive for MHC don't normally have many illnesses because they don't produce these MHC-antigen complexes.
D) MHC inheritance is X-linked and thus males will have a higher percentage of weak immune systems than females do.
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