How can you get 4:0 (grande:petite) but not 0:4 when you sporulate the r- diploid?
The r- diploid is heteroplasmic. There are enough wt mitochondria to be able to override the r- in at least 1 spore in a tetrad. After a few mitoses, however, there are far too many r- mitochondria (in a suppressive r-), the cell is essentially homplasmic, and so sporulation of a petite from this population always produces 0:4 (all petite). After several mitoses, a grande cell is homoplasmic too, so sporulation of a grande from this population will give 4:0 (all grande).
