Rocky mountain juniper (juniperus scopulorum) and one-seeded juniper (j. monosperma) have overlapping ranges. pollen grains (which contain sperm nuclei) from one species are unable to germinate and make pollen tubes to bring the sperm nuclei to the female ovules (which contain egg cells) of the other species. these two juniper species are kept separate by

Mechanical isolation

Mechanical isolation occurs when two organisms of the same species are unable to copulate because of the differences in their reproductive organs. In flowering plants, differences in the structure of the reproductive parts may also hinder pollination. From the question given above, even though the two plants have overlapping ranges, the pollen grains from one species are unable to grow thus disallowing the pollen tubes to connect or transport the sperm nuclei to the female ovules of the other species where the fertilization of the eggs will occur. These two species are said to be isolated mechanically.

answer; i believe that the correct answer is ; males are hemizygous for the x chromosome;

very