Grammar - genitive

study ex 1 ex 2
 
1. Possessive case
To make the genitive of nouns of PEOPLE or ANIMALS we add 's
My mother's hobby is surfing.
The yellow one is my dad's car.
To plural of nouns of PEOPLE or ANIMALS ending in -s we add ' (apostrophe)
The cats' food is in the kitchen.
Where is the ladies' room?
To proper nouns (name) ending in a sibilant (=sound like an S) we add an 's
Prince Charles's wedding was in 1981.
We walked through St James's park.
 
2. Special use
When THE PLACE IS UNDERSTOOD, 
words such as house, shop, cathedral,...are generally omitted after a genitive:

The wedding took place at St Paul's. (Cathedral)
Mum is at the baker's. (shop)
I'm staying at my uncle's. (house)
The genitive is often used in EXPRESSIONS denoting TIME or DISTANCE:
Where is yesterday's newspaper?
We go to Bath for a week's holiday.
She lives in an hour's distance from work.
Sometimes a noun is followed by OF + GENITIVE: it is called the double possessive 
and is used to put the stress on the person who possesses:

This is a house of my sister's.
These are friends of my father's.