Scientists commonly choose white blood cells that are going through mitosis to prepare karyotypes. Why?

This is because during the phase of mitosis, chromosomes of the white blood cells condense.

Explanation:

A karotype tells us about the appearance of a chromosome which involves the number of the chromosomes as well as the structure of the chromosomes.

Karotype can be used to detect any defect or abnormalities that can lead to sicknesses or health disorders in a person.

In order to prepare a karotype, white blood cells going through mitosis is used because during mitosis the chromosomes of the white blood cells condense thereby making movement easier for the cells.

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.