Expected frequency of tetrad spores with Tetratype?

[sproti]

This problem is written in my language (not english) so I'll try to translate it the best I can. I've spend the last hour trying to figure this out but I just can't understand this problem.

-------------------

The fungi S. cerevisiae creates tetrad spores. How high of a ratio can be expected of tetrad spores with tetratype (both parental types and recombinants) if there are 14 map units between genes?

A. 7%

B. 14%

C. 28%

D.72%

E. 86%

-------------------

So I assume what they mean is basicly among PD (Parental ditype), NPD (Nonparental ditype) and T (Tetratype) what ratio of tetrad spores has the tetrad type. I understand that the tetrad type itself will have parental types of 86% (43% each) and recombinants will have 14% (7% each) but I have no idea how I figure out the ratio of tetratypes.

Edited May 18, 2013 by sproti