Alien gene mapping

Here's an example I used in class a little while ago.  Lucky for us, the aliens exhibit Mendelian dominant/recessive characteristics!  They're also diploid, and have linear chromosomes.

Here's the setup:
You discover an alien species that displays the same type of inheritance that is commonplace with diploid animals on Earth. You cross two true-breeding individuals and the F₁ displays these traits:  pear-shaped head, gray skin, and normal fingers.  The F₁ is testcrossed to give the following data:

		Cross of aliens
91		pear-shaped head, glowing fingertip, and green skin
6		pear-shaped head, glowing fingertip, and gray skin
1		pear-shaped head, normal fingertip, and green skin
1		round head, glowing fingertip, and gray skin
7		round head, normal fingertip, and green skin
506		pear-shaped head, normal fingertip, and gray skin
85		round head, normal fingertip, and gray skin
491		round head, glowing fingertip, and green skin

_{Define gene symbols and create a genetic map that shows how these traits are arranged on the chromosomes.  Be sure to mathematically correct for double crossover events.  Calculate interference.}