Spelling of stems and suffixes; writing together

When a suffix is added to a stem, a vowel in the stem sometimes changes, and this is shown in writing. When -v, -q, -qi, -vchi are added to a verb ending in a, o is written instead of a: tara — taroq (comb), to‘la — to‘lov (payment), saqla — saqlovchi (keeper), yasha — yashovchi (resident). In some verbs ending in i, the i turns into u: o‘qi — o‘quvchi (pupil), qazi — qazuvchi (digger). Suffixes beginning with g are written with g, k or q depending on the previous sound: kelgan, ko‘kka, yoqqan. But in words ending in g or g‘ neither the stem nor the suffix changes: geologga, bog‘ga.