Question

A v-onc gene may be found in
A. bacteriophages
B. human cells
C. retroviruses
D fowl
E. bacteria

Answer 1

The "v" in "v-onc" stands for "viral"

Answer 2

I'm interested in the answer and an explanation as well. Do you mind elaborating, @jc7 ?

This is from Wikipedia ( http://en.wikipedia.org/wiki/Carcinogenesis)
"Furthermore, many cancers originate from a viral infection; this is especially true in animals such as birds, but less so in humans. 12% of human cancers can be attributed to a viral infection.[27] The mode of virally-induced tumors can be divided into two, acutely-transforming or slowly-transforming. In acutely-transforming viruses, the viral particles carry a gene that encodes for an overactive oncogene called viral-oncogene (v-onc), and the infected cell is transformed as soon as v-onc is expressed. In contrast, in slowly-transforming viruses, the virus genome is inserted, especially as viral genome insertion is obligatory part of retroviruses, near a proto-oncogene in the host genome."

If I'm understanding this correctly, choices B and D both seem to be acceptable.

Answer 3

Viral oncogenes are present in viral genomes. In most cases, they are homologues of cellular proto-oncogenes. For example, the first viral oncogene characterized is v-src, a gene present in Rous sarcoma virus. This is a retrovirus that makes a DNA copy of it's genome in infected cells, and the viral genome integrates into the infected host cells chromosomal DNA. There the v-src gene causes unregulated cell growth, creating a tumor. Further study showed that normal, uninfected cells contain a similar gene, called c-src. We now understand that c-src has a role in regulating mitotic growth of cells. One can generalize that most viral oncogenes (v-oncs) are homologues of cellular growth regulating genes (c-oncs or proto-oncogenes). So the correct answer to this question would be C retroviruses. v-oncs are present only in tumorigenic retroviruses. They can become part of a cell's DNA only if the cell is infected by an oncogenic retrovirus.

Answer 4

Thank you.