Fungi like Neurospora and Sordaria that have an ordered tetrad can be used to map a gene's location relative to its centromere.

To preform this cross, place two squares of a mutant strain (either tan spores, tn, or gray, g) as indicated below on the crossing agar. Then place two wild type squares as indicated below.

After 7-12 days, check the perithecia (tiny black bodies at the edge) for hybrid asci. Pick a few off from the indicated spot with a toothpick and place them on a slide with a drop of water and add a coverslip. Press on the coverslip with a pencil eraser until the perithecia burst. Examine the slide under the microscope to see if there are any asci with both dark and light spores (hybrid asci). If not, try again. The arrows below show the most likely places to find hybrid asci. When you find hybrid spores, count a total of 100 hybrid asci recording how many show first division segregation and how many show second division segregation. From this data, you should be able to calculate the distance between the gene (tn or g, whichever one you chose) and its centromere.

This exercise will be written up as a "formal" lab report. For this first lab report only you may freely cooperate with others in the writing of the exercise.