Question

Why is it not possible for an alien DNA to become part of a chromosome anywhere along its length and replicate normally?

Answer 1

Hint: DNA is the hereditary material of eukaryotes and higher animals.

Complete answer: Alien DNA cannot become part of the chromosome anywhere along its length and replicate normally because in order to ligate itself to the host chromosome alien DNA requires specific recognition sequences.
The sequence should also be close to the origin of replication or Ori where DNA replication starts. This site is necessary for the binding of the DNA polymerase to start replication.
As this site may not be present in all alien DNA molecules, so an alien piece of DNA cannot replicate normally by attaching to any DNA.

Additional information: DNA replication is the biological process of producing two identical copies of DNA from one original DNA molecule.
DNA replication occurs in all living organisms acting as the most essential part of biological inheritance.
DNA replication begins at specific locations, or origins of replication, in the genome.
The unwinding of DNA at the origin and synthesis of new strands, accommodated by an enzyme known as helicase, results in replication forks growing bi-directionally from the origin.

Note: A number of proteins are associated with the replication fork to help in the initiation and continuation of DNA synthesis.
DNA polymerase synthesizes the new strands by adding nucleotides that complement each (template) strand.
DNA replication occurs during the S-stage of interphase.