Final answer:
The most direct cause of polyteny in somatic cells of certain organisms is chromosome replication without cell division.
Step-by-step explanation:
The most direct cause of polyteny in somatic cells of certain organisms is chromosome replication without cell division (Option C).
Polyteny is the phenomenon where multiple copies of homologous chromosomes are present in a single nucleus. This occurs due to repeated rounds of DNA replication without cell division, resulting in an increase in chromosome number.
For example, in certain species of insects, such as the fruit fly Drosophila, polyteny occurs in the salivary glands. The increased number of chromosomes allows for the production of large amounts of specific proteins, such as salivary gland secretory proteins, which are needed for the insect's survival and reproduction.
Learn more about polyteny