Dotted and dotless I are two different letters in the Turkish alphabet. One of them (İ, i) has a dot above it and the other (I, ı) does not. This is true in both the capital and lower case forms of the letters (see the picture).
The dotless I has the /ɯ/ sound, while the dotted İ has the /i/ sound. To show how they are pronounced, here are two examples:
Some of the other Turkic languages that use the Latin script, like Azerbaijani and Tatar, also use both kinds of I. But in all these languages, including Turkish, the letter j does not have a dotted or dotless form, with a dot only on the lower case character (J, j), just like in the Indo-European languages. However, a dotless j, ȷ, does exist in Unicode.