ethics - Is it ethical for a professor to get a graduate student to complete a manuscript peer review that the professor has been assigned?

Is it ethical to a professor to accept a manuscript for review, and then have a graduate student referee it? What about assisting as a referee?

I understand that graduate students can be involved in the review process- this isn't my question. As far as the journal/editors are aware, the professor is the referee, but in actuality, the student is performing the review.

If an assigned referee would like a student to participate, how could this be done properly?