C++ :: How To Initialize Vector In A Class Object

I want to make a class, named generation, having a vector<chromosome> type data member.

chromosome is also class name.

chromosome has a 'route' as data member, which type is class TArrayI defined in ROOT package.

the size of route is to be fixed according to parameters of generation class object.

class chromosome{
public: chromosome(){;}
....
protected:
TArrayI route;
};
class generation{
public: generation(int PopSize=300, int numCity = 36){
.........
}
vector<chromosome> Population;
};

I want each element, chromosome of Population, to have a numCity size of route.