Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight, and mutations to the dna in their skin cells are left uncorrected. why are the mutations not corrected in individuals with this disorder?

This disease is caused by mutations in 8 genes involved in DNA repair. Seven of these genes are involved in nucleotide excision repair. Some of the genes involved code for DNA polymerase, which is necessary for DNA replication with UV-induced damage.

The wavelength of ultraviolet light, which oscillates between 280 and 340 nm, induces a DNA or nucleotide lesion, under normal conditions the cells have the capacity to repair this damage, in people with this disease there is a defect in excision. Nucleotide repair by an alteration in the enzyme that is responsible for the repair of nuclear DNA in the course of mitosis.

one would be wind another would be water density

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.