Calculating Interference two ways

I've demonstrated above that I calculate interference by comparing the ratios of DCO offspring (observed/expected).  It's simply a ratio to show what percentage of DCOs you see in the offspring compared to what you're expecting.

The McGraw-Hill Hartwell et al. textbook uses the ratio of obs DCO frequency to exp DCO frequency.

In my method, you calculate the expected DCO frequency and multiply it by the total number of offspring to figure out how many you should have seen.

In the book's method, you use the calculated DCO frequency, and convert the observed number of offspring into a frequency.

Basically, it's the same number of steps.  That said, I can understand why this might be confusing and so I made a video of it (in part because the book's way of doing it confused me at the end of class and I made a fool of myself.

Here's my apology.  But you can go a little further ... here are the ratios and you can calculate the distances yourself.  Don't bother making new gene symbols; they did that for you.  The eight rows represent all the progeny from a cross between a het and a tester.

In my video below, you see the distances, and two ways to calculate interference from it.  Try it out yourself before going to the video.