Question

The formation of heterochromatin begins at a site, continues by ________ in both directions, and stops when a site is reached.

1) replication
2) transcription
3) translation
4) recombination

Answer 1

The formation of heterochromatin continues by 'replication' in both directions; it begins at a specific site and ends upon reaching another such site or termination signal.

Step-by-step explanation:

The formation of heterochromatin begins at a site, continues by spreading in both directions, and stops when a site is reached.

The correct term to fill in the blank is 'replication' because heterochromatin formation is associated with the DNA replication process, in which the DNA unwinds at the origin of replication, and helicase forms replication forks that are then extended bidirectionally.

During the replication process, single-strand binding proteins prevent the DNA from rewinding, while topoisomerase prevents supercoiling ahead of the replication fork.

DNA polymerase adds nucleotides to the new strands, and the whole process continues until it reaches a termination point or another bound protein that stops replication.

Answer 2

Answer: recombination

Explanation: The formation of heterochromatin begins at a site, continues by recombination in both directions, and stops when a site is reached. Heterochromatin formation involves the modification and condensation of chromatin structure, often associated with silencing of gene expression or inactivation of certain genomic regions. Recombination processes contribute to the spreading of heterochromatin by modifying neighboring chromatin regions and forming a compact and condensed chromatin structure.