What evidence supports the proposal that MHC diversity evolved by natural selection caused by infectious pathogens rather than exclusively by random DNA mutations?
What will be an ideal response?
MHC polymorphisms are non-randomly localized, predominantly to the region of the molecule that makes contact with peptide and T-cell receptors. Random DNA mutations, in contrast, would be scattered through the gene, giving rise to amino acid changes throughout MHC molecules and not just in those areas important for peptide binding and presentation.
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Peptic ulcer disease does NOT occur in the:
A) stomach. B) duodenum. C) colon D) esophagus.
Which of the following poses the greatest threat to Joan?
A. a nasty hangover B. alcohol poisoning C. disorientation D. swimming injuries
What type of program is typically offered by employers and large institutions that want to provide some level of medical assistance but do not want to pay for full insurance?
A) health discount program B) co-pay C) managed-care plan D) All of the answers are correct.
People who have experienced repeated failures may develop a pattern of response in which they give up and fail to take any positive action. This is called
A) resistance. B) learned helplessness. C) learned optimism. D) laziness.