4. Haploid cells have

Haploid cells contain a single set of chromosomes. Gametes are an example of haploid cells produced as a result of meiosis. Examples of gametes are the male and female reproductive cells, the sperm and egg cell respectively.

Explanation:

Haploid describes a cell that contains a single set of chromosomes. The term haploid can also refer to the number of chromosomes in egg or sperm cells, which are also called gametes. In humans, gametes are haploid cells that contain 23 chromosomes, each of which a one of a chromosome pair that exists in diplod cells.

it would be c. xylem.

"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."