A test cross can be used to .

cross-breed dominant and recessive plants
give probabilities that a trait will appear
predict the phenotypes of a monohybrid cross
predict an unknown genotype of a purebred dominant plant

Umm I'm not sure about a purebred  dominant plant but test crosses are used to find unknown genotypes by crossing the animal with an organism containing homozygous recessive genes, sooo...

i dont know this but ask your teacher for !

"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."