42. Many tumor cells are able to divide uncontrollably in cell culture in the laboratory. Some of these cell lines have genomes with a mutant tumor suppressor gene...

Question

1) Many tumor cells are able to divide uncontrollably in cell culture in the laboratory. Some of these cell lines have genomes with a mutant tumor suppressor gene. By adding a wild-type copy of this tumor suppressor gene to the genomes of these cells, they have a reduced ability to divide in culture. In contrast, adding a wild-type copy of a proto-oncogene to the genomes of a tumor cell line with an activated oncogene doesn’t have any effect on the uncontrolled cell division shown by this line. Which of the following statements best explains why adding a wild-type proto-oncogene doesn’t affect cell division in these cell lines?

A. Most point mutations that produce activated oncogenes are dominant gain-of-function mutations.

B. Many proto-oncogenes encode proteins that act to promote apoptosis.

C.Many proto-oncogenes encode proteins involved in DNA repair.

D.Many proto-oncogenes are inherited as recessive mutations.

E. Most protein products of proto-oncogenes do not have a role in cell division.

2) Posterior development of a Drosophila embryo requires the Nanos protein in the egg prior to fertilization. Otherwise, the embryo will develop two heads if Nanos protein is not present. The loss-of-function nano- mutation is recessive and exhibits a maternal effect. Which of the following correctly describes the embryos produced from a cross between a nano+/nano- male and a nano-/nano- female?

A. All embryos will be normal.

B. All embryos will have two heads.

C.Three-fourths of the embryos will have two heads.

D.One-half of the embryos will have two heads.

E. One-fourth of the embryos will have two heads.

Answer 1

Oh, this should be fun. For the first question, I'm going to use one of those naughty words in biology that one should never use: always. All mutations in proto-oncogenes that "convert" them to oncogenes are always dominant because they gain a new function. So, adding a wild-type version of a proto-oncogene (which, technically, is a misnomer as all proto-oncogenes are "wild type by definition", whereas the mutated "activated" version are just called oncogenes) does nothing because the cells still have one bad copy of the gene, and because it's a dominant mutation, will not be silenced or constrained For tumor suppressors, they must have 2 bad copies in order to cause a problem, so introducing at least one good allele is enough to stop cells from increasing in number. So the correct answer is A. Does that make sense?

This second question is far less fun. Your teacher seeks to deceive you There are 2 quintessential clues in this question that determines the answer. 1) nano is a protein that's present in the egg already and because of that 2) comes only from the mother. The male's ability to make this protein is entirely irrelevant. 3) this is a loss-of-function mutation meaning you need too bad alleles for the phenotype. So, when we get to the cross at the very end, we only need consider the genotype of the female; the female is -/- (so wouldn't she have two heads? Would she even be viable????? It's best not to think about these matters) meaning 100% of that protein she deposits into her eggs will not be functional, meaning the correct answer is B - all offspring will have 2 heads

Hope that helps!