Many times, students struggle, with the difference between the terms alleles and gene. how would you explain the difference of these two terms in a way that memorable to you

Unlike  ct scans, which use x-rays,  mri scans  use powerful magnetic fields and radio frequency pulses to produce detailed pictures of organs, soft tissues, bone and other internal body structures.  differences between  normal and abnormal tissue is often clearer on an  mri  image than a  ct.you can see more with a mri scan. for example on an mri you can see internal bleeding.

Avaccine? hiv preventing, of course.