The mechanisms of reproductive isolation prevent the reproduction of two individuals from different species. The prezygotic mechanisms disrupt the stages of reproduction before the forming of the zygote or prevent the mating at the start, and the postzygotic mechanisms affect the stages of reproduction after the forming of the zygote.
So, the first and the third example (the urchins and the grasshoppers) show the prezygotic mechanism, as the two individuals are not able to mate or form a zygote.
The second and the fourth example ( zonkey and the death of a zygote) show the working of the postzygotic mechanisms, as the zygote is formed, but it seems to be inviable, and the zonkeys are sterile, preventing the individual to reproduce.
Answer:
While doing medical research on the human subject, following limitations are unavoidable:
a). Privacy: The privacy of the subject involved in the research should be maintained.
b). the subject must be allowed to the minimal exposure to risks and it must be tested on animals first to avoid deaths.
c). The risk associated with the physiological and physical well being of the subject must be considered.
d). The subject must be well instructed about all the risk and procedure involved in the research.
The magnification will provide better visibility and more detailed information.
The answer is Testicles (testes)
that will be temperature cause the mass will either have to increase or decrease
