Give a brief description of the factors involved in understanding the etiology of a disease.

Relatedly, when disease is widespread, epidemiological studies investigate what associated factors, such as location, sex, exposure to chemicals, and many others, make a population more or less likely to have an illness, condition, or disease, thus helping determine its etiology.  

Location, sex, and exposure to chemicals make a population more or less likely to have an illness. This helps determine the etiology when the disease is widespread.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.