Q. "Therefore, for the multiplication of any alien piece of DNA in an organisms it needs to be a part of a chromosome(s) which has a specific sequences known as 'origin of replication'. " Explain the above lines. 
Won't all chromosomes have their own origin of replication?

Dear Student,

Every chromosome has a region called the "origin of replication". This is the starting point of replication. Alien DNA is often attached to the chromosome having an origin of replication for multiplication. 

Now, the answer to your second part of your question. Yes, all chromosomes have their own origin of replication. The number of origin of replication in a chromosome differs from organism to organism. 

Regards,
Pavithra.