Team CryptoInsightfull 
Seeds are not stored on the blockchain. Rather seeds are used to generate private keys, which are then used to create digital signatures, which serve as proof that the owner of it agrees to the transaction.
Bitcoin transactions create transaction outputs that contain the value in Bitcoin assigned to them, as well as the conditions required to spend that output as an input to another transaction. The owner of that output, and therefore the Bitcoin value associated with it, is the persons who can satisfy the conditions specified in the output. The most common condition is that of a digital signature – the output specifies a public key (or its hash) and so the condition is that the spending input must contain a digital signature created by the private key corresponding to the specified public key.
As their name suggests, public keys are meant to be public and can be shared publicly without exposure of the private key. The private key, as the name suggests, must be kept private. It is then used to generate the signature. The math works out such that it is not possible to compute the private key for a public key, nor is it possible to create a signature for that public key without also having the private key.
A seed is simply another private key, as it is used to generate other private keys. Although seeds are not typically used directly as private keys for producing signatures.
Lastly, Bitcoin does not require any sort of registration of public keys when their private keys are generated. The space of possible private keys is so large that it is basically impossible for two people to generate the same private key if they are generating their keys correctly. However, given that ownership is basically defined as the ability to spend an output, if private keys are improperly generated, or an output has insecure spending conditions, multiple people may “own” the output and be able to spend it independently of each other.
