In this problem we will explore some of the many ways that mutations in two different genes can interact to produce different Mendelian ratios. Consider a hypothetical insect species that has red eyes. Imagine mutations in two different unlinked genes that can, in certain combinations, block the formation of red eye pigment yielding mutants with white eyes. In principle, there are two different possible arrangements for two biochemical steps responsible for the formation of red eye pigment. The two genes might act in series such that a mutation in either gene would block the formation of red pigment. Alternatively, the two genes could act in parallel such that mutations in both genes would be required to block the formation of red pigment.

Further complexity arises from the possibility that mutations in either gene that lead to a block in enzymatic activity could be either dominant or recessive. If the crosses between a wild type insect with red eyes and a true breeding white eyed strain with mutations in both genes. Such considerations yield the Pathways in parallel with a recessive mutation in one gene and a dominant mutation in the other, determine the phenotype of the F1 progeny and the expected phenotypic ratio of red to white eyed insects in the F2.

#Question id: 1501

#Unit 4. Cell Communication and Cell Signaling

When a culture of rodent cells is infected with a DNA tumor virus whose gene products bind to p53 and RB, all the cells take on characteristics of malignancy. If the viral gene coding the p53-binding protein is mutated, but that coding for the RB-binding protein is not mutated, how will infected cells respond?

#Question id: 1502

#Unit 4. Cell Communication and Cell Signaling

The textbook states that cells of patients with adenomatous polyposis coli (APC) “contain a deletion of a small portion of chromosome #5, which was subsequently identified as the site of a tumor-suppressor gene called APC.” In which cells of these patients would you expect to find this chromosomal deletion?

#Question id: 1503

#Unit 4. Cell Communication and Cell Signaling

When the genes responsible for familial breast cancer were sequenced, it was found that the polypeptides they encoded contained a zinc finger motif. What does this suggest to you about the normal functions of the products of these genes?

#Question id: 1504

#Unit 4. Cell Communication and Cell Signaling

Tumor-suppressor genes usually act as .......... genes, and oncogenes usually act as ...........  genes.

#Question id: 1505

#Unit 4. Cell Communication and Cell Signaling

Which of the following types of genes have not been identified as oncogenes?

#Question id: 1506

#Unit 4. Cell Communication and Cell Signaling

An oncogene codes for a growth factor receptor that is constitutively active. Of the following statements about a culture of cells expressing this gene, which would you expect to be true?