chapter 1

The stage of the cell cycle where the cell is preparing to begin DNA replication is called:

A. G1 Correct. Yes, G1 cells are preparing for S

The Thompson seedless grape is triploid, with three copies of each chromosome. Which phase of the cell cycle would you expect triploid cells to be unable to complete.

A. meiosis 1 Correct. True, homologous chromosomes must pair in meiosis I. Triploid cells would be unable to complete meiosis I.

The Biology Project > Cell Biology > Meiosis > Problems Meiosis Tutorial Problem 1: Number of chromosomes A human cell has 46 total or 23 pairs of chromosomes. Following mitosis, the daughter cells would each have a total of ______ chromosomes. After meiosis I, the two daughter cells would have _____chromosomes, and after meiosis II ______ chromosomes.

B. 46, 23, 23 Correct. The chromosome number is reduced to one half during the first meiotic division. Recall that the number of chromosomes is determined by the number of centromeres, and not the number of chromatids.

The sputum (fluid coughed up from the lungs) of many smokers contain cells with mutations (errors) in the genes for p53. The smoking induced mutations appear to be an early signal showing that cancer of the lungs will follow. What is the likely relationship between early p53 mutation and the development of lung cancer?

B. Mutations in p53 would prevent abnormal cells from dying by apoptosis. Correct. If the mechanism for eliminating abnormal cells is defective, then the cells will continue to divide and further damage their DNA. This process leads to cancer. Exposure to sun also causes apoptosis in damaged cells. This produces the familiar peeling and blistering associated with severe sunburn. Over many years, exposure to sun also leads to cancer. It is particularly interesting that smoke seems to cause a high frequency of p53 mutations.

During anaphase, a free kinetochore formed by disrupting an attached spindle fiber results in an immediate block to the process. This result shows that:

B. The cells have mechanisms to insure that errors are not made during anaphase. Correct. This observation is entirely correct. Scientists are now working on the mechanisms by which detachment is detected, a process probably involving phosphorylation

Coral in the ocean grows by budding, where the new organism grows out of the old one by mitosis. This form of replication is an example of:

B. asexual reproduction Correct. Yes, and can produce large numbers of organisms but without genetic diversity.

The first stage of mitosis when chromosomes start becoming visible in the microscope is called:

B. prophase Correct. Yes, at the beginning of prophase, the chromosomes condense into structures visible in the light microscope.

The process of meiosis produces four cells with nonidentical chromosomes. This diversification occurs during:

B. prophase 1 Correct. Prophase I includes recombination of genetic material and the random arrangement of the homologous pairs, producing diversification of the resulting haploid cells.

The stage of meiosis where cells become haploid.

C. anaphase I Correct. Separation of homologous pairs occurs at anaphase I. Even though each chromosome has two chromatids, the total number of chromosomes is 23 for humans after anaphase I of meiosis I. Recall that the number of chromosomes is determined by the number of centromeres.

The class of enzymes that are involved in triggering events in the cell cycle are called:

C. kinases Correct. Yes, kinases add phosphate to molecules, and the modification can serve as a "switch" to turn events in the cell on or off. Cdk or cyclin dependent kinases regulate the cell cycle.

Cytokinesis in a plant cell is characterized by:

C. the formation of a cell plate in the cytoplasm Correct. Yes, the spindle fibers are used to bring in vesicles that line up along the cell plate and produce a new cell wall.

Which sequence of the cell cycle is common to eukaryotes?

D. G1 to S to G2 to M to cytokinesis Correct. The correct sequence has G1 as a preparation for S and G2 as the time between the completion of S and entry into M. Cytokinesis occurs after the other stages to create two daughter cells.

The stage of the cell cycle where each chromosome is composed of two chromatids in preparation for mitosis.

D. G2 Correct. Yes, S resulted in the duplication of each chromatid. Since there is only one centromere on the sister chromatids, we still call them one chromosome. When completed, the cells are in G2 and preparing for M.

Which of the following statements is NOT true of mitosis?

D. Homologous chromosomes synapse in prophase. Correct. Homologous chromosomes are independent in mitosis and synapse or line up only in prophase I of meiosis

One of the earliest events that distinguishes meiosis occurs in prophase I and involves:

D. Pairing of homologous chromosomes Correct. Pairing of chromosomes is unique to meiosis, and allows crossing over.

Some organisms are capable of asexual or sexual reproduction. Under favorable conditions, reproduction proceeds asexually. When conditions become more stressful reproduction switches to a sexual mode. Why?

D. Sexual reproduction produces individuals with new combinations of recombined chromosomes increasing diversity. Correct. This answer provides the reason for sexual reproduction, and also interestingly enough, the reason for death. Our species survives if we increase variation by meiosis.

Which of the following features of cell division are very different for animal and plant cells?

D. cytokinesis Correct. Yes, the animal cell can pinch into two by a ring of microfilaments. The plant cell with a rigid wall synthesizes a new cell plate. In both cases, the spindle fibers play a role in determining the site where the cell is split.

The proteins which complex with DNA producing the "beads on a string" or nucleosomes are called:

D. histones Correct. Yes, the histones form structural complexes with DNA. In the electron microscope, these can take the appearance of beads on a string.

Which of the following is unique to mitosis and not a part of meiosis?

D. homologous chromosomes behave independently Correct. Pairing of homologous chromosomes allowing independent segregation and crossing over is unique to meiosis. In mitosis, homologous chromosomes behave independently.

The Biology Project > Cell Biology > Meiosis > Problems Meiosis Tutorial Problem 9: Phases of meiosis _________________ most closely resembles events of mitosis except that the cells are ___________.

D. meiosis II, haploid Correct. Yes, meiosis II events are similar to mitosis with haploid cells.

Prior to cell division, each chromosome replicates or duplicates its genetic material. The products are connected by a centromere and are called:

D. sister chromatids Correct. Yes, the replication of the chromosome begins with the production of sister chromatids. The complex is considered to be one chromosome since there is only one centromere.

What is DNA and where is it stored?

DNA packs tightly into metaphase chromosomes