There are two very different things that take the form •'s:
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as the clitic version of a verb, is, has, and sometimes was and does; 2) as the genitive/possessive case marker.
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can be attached at the end of all noun phrases, even when the noun phrases is a single pronoun, like it: it’s=it is, it has (or it was and it does in some dialects).
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can be attached to all noun phrases except to personal pronouns. These inflect, they change their forms: I>my, mine; you>your, yours; he>his; she>her, hers; it>its; we>our, ours; they>their, theirs.
Historically, the genitive case marker •'s originated from inflectional morphology in the form of •es. Different classes of nouns would have different case markers but the •es version ended up prevailing over the others as english shed its case system. The apostrophe that turned •es into •'s seems to have come from imitating the french practice of using an apostrophe where a vowel wasn’t pronounced anymore.
I can get two whoppers for about 5 dollars and they are full of flavor over here (Brazil).