All GRE Subject Test: Biology Resources
Example Question #1 : Understanding Cell Division, Mitosis, And Meiosis
A scientist has discovered a mutation that prevents cells from passing anaphase of mitosis. Of the following options, which is the most likely target of the mutation?
Proteins involved in chromosome condensation
If the cell cannot progress past metaphase, the cell is most likely having trouble separating the sister chromatids. This process is mediated by attaching the kinetochore microtubules to the kinetochore on the sister chromatids. Our most likely explanation for a problem proceeding past metaphase is that the mutation is affecting the formation of microtubules. The progression from metaphase to anaphase is regulated by the metaphase checkpoint in the cell cycle, which is used to ensure proper attachment of spindle fibers to the centromeres. Problems with spindle fiber formation and binding would cause the cell to be arrested in metaphase.
Actin and myosin are not directly involved in this portion of mitosis, but are very important during cytokinesis. Chromosome condensation has already occurred (during prophase), so our mutation cannot be affecting those proteins.
Example Question #2 : Understanding Cell Division, Mitosis, And Meiosis
Which phase of mitosis involves the separation of chromatids?
Cellular division usually takes place in four steps before undergoing cytokinesis. In prophase, the chromosomes condense and become visible, and the spindle apparatus begins to form. In metaphase, the chromosomes line up on the equator of the cell. In anaphase, the chromatids are pulled apart and separated to opposite sides of the cell. Finally, telophase involves the nuclear membrane reforming around the chromosomes, which begin to decondense.
Example Question #3 : Understanding Cell Division, Mitosis, And Meiosis
Which phase of mitosis is characterized by the reappearance of the nuclear envelope?
Once the cell has split and transported its sister chromatids to opposite ends of the cell, the nuclear envelopes can begin to regenerate around the genetic material at each pole. This event occurs during the end of mitosis, commonly known as telophase.
Example Question #7 : Mitosis And Meiosis
Combrestatin is a drug that prevents the polymerization of microtubules. Which of the following processes would be most affected by combrestatin?
Combrestatin interferes with the formation of microtubules, which make up the cytoskeletal architecture of a cell; therefore, the correct answer choice is involved with some microtubule-based process. DNA and protein synthesis do not involve microtubules, and would not be affected by the lack thereof. Muscle contraction depends on myosin, actin, troponin, etc., and not on microtubules. Membrane depolarization involves sodium/potassium channels, neurotransmitters, etc., and is not directly affected by microtubule inhibition.
The only answer that remains is mitosis, which involves microtubules in chromosomal segregation. The mitotic spindle in this separation is primarily composed of microtubules. The polymerization and depolymerization of microtubules is crucial for mitotic division. Combrestatin therefore prevents proper mitosis.
Example Question #4 : Understanding Cell Division, Mitosis, And Meiosis
Crossing over occurs during which stage of meiosis?
In the process of meiosis, crossing over (the exchange of genetic material between homologous chromosomes resulting in recombination) only occurs during prophase I, when pairs of homologous chromosomes recombine during synapsis. This contributes to the increase in diversity due to sexual reproduction.