BY 123 SI Session #7 Answer Key

Chapter 12

1)How many chromosomes are in your somatic cells?-46

2)How many chromosomes are in your gametes?-23

3)How many chromatids are in one of your somatic cells that has duplicated its chromosomes prior to mitosis?-92

4)True or False: Cell division and Cytokinesis is usually the longest part of the cell cycle, compromising about 90%.

5)Match the following stages of the cell cycle with their proper description:

  1. G1 phase
  2. G2 phase
  3. S phase

__c___ cell continues to grow as it copies its chromosomes

__a___ cell growth

__b___ cell grows as it completes preparation for cell division

6)Match the following checkpoints of the molecular control system with its correct description:

  1. G1 checkpoint
  2. G2 checkpoint
  3. M checkpoint

__b____ checkpoint before the cell enters cell division and cytokinesis

__a____ the “restriction checkpoint” which is usually the determining checkpoint for the cell to move to all other phases of the cell cycle.

__c____ checkpoint before cytokinesis

7)Are most of the cells in the human body in a dividing phase? Give an example of a cell that would never be diving. Give an example of a cell that can be “called back” by growth factors.

No, most are in G0 phase. An example of cells that would never be dividing are nerve and muscle cells. Liver cells, however, can be called back by growth factors. They would then enter the G1 phase and undergo mitosis.

8)Identify the appropriate phase of the cell cycle:

__G0 phase____ most cells that will no longer divide are in this phase

__Anaphase____ sister chromatids separate and chromosomes move apart

_Prophase_____ mitotic spindle begins to form

_Cytokinesis_____ cell plate forms or cleavage furrow pinches cells apart

__S phase____ chromosomes duplicate

__Metaphase____ chromosomes line up at central plane

__Telophase____ nuclear membranes form around separated chromosomes

_Prophase_____ chromosomes become visible

__G1 phase_____ restriction point occurs in this phase

9)What is the difference between cyclin, CDK’s and MPF? What is a simple way to remember MPF’s? –cyclin is a protein. CDK’s areCyclin dependent kinases and their concentration rises and falls with cyclin concentration. Cyclin and CDK’s form a cyclin-CDK complex. MPF’s are Maturation promoting factors, however an easy way to remember them is “Metaphase promoting factor”. The concentration of MPF fluctuates, increasing when cyclin-CDK complex increases.

10)When would cyclin levels be the highest? When would MPF levels be the highest?

-Cyclin levels would be the highest during S and G2 phases before they are getting ready to divide. MPF levels would also be the highest then because it is directly proportional. Figure 12.17 on page 240.

11)Which of the following would NOT be exhibited by cancer cells?

  1. Changing levels of MPF concentration
  2. Passage through the restriction point
  3. Density-dependent inhibition
  4. Metastasis
  5. G1 phase of the cell cycle

12)A drug blocks the function of actin in the cell. Which of the following functions of the animal cell would be most affected by this drug?

  1. DNA synthesis
  2. Cell elongation during anaphase
  3. Cleavage furrow formation and cytokinesis ( because of microfilaments)
  4. Spindle formation
  5. Spindle attachment to kinetochores

13)Draw and label the stages of the Mitosis in an Animal cell: (Interphase, Metaphase, Prophase, Anaphase, and Telophase)

Page 232-233 of Campbell textbook

Chapter 13 : Genetics

1)How many chromosomes are there in the somatic cells of an animal in which 2n = 14? How many chromosomes are in its gametes? --14 in somatic cells, 7 in gametes

2)If n=14, how many chromosomes are there in diploid somatic cells? How many sets of homologous chromosomes are in the gametes?—28 in diploid somatic cells, 1 chromosome in each gamete

3)If 2n=28, how many chromatids are there in a cell in which DNA replication has occurred prior to cell division? What is the difference between sister chromatids and non sister chromatids?

--56 chromatids

--Sister chromatids are produced when a chromosome duplicates before cell division. They are joined at the centromere and attached along their lengths. Non sister chromatids are found on different chromosomes of a homologous pair.

4)How many chromatids are present in metaphase II in a cell undergoing meiosis from an organism in which 2n = 24?

  1. 12
  2. 24
  3. 36
  4. 48
  5. 96

5)In a species with a diploid number of 6, how many different combinations of maternal and paternal chromosomes would be possible in gametes?

  1. 6
  2. 8 because 23
  3. 12
  4. 64
  5. 128

6)Which of the following is LEAST likely to be a source of genetic cariation in sexually reproducing organisms?

  1. Crossing over
  2. Replication of DNA during S phase before meiosis I
  3. Independent assortment of chromosomes
  4. Random fertilization of gametes
  5. All of the above contribute equally to the genetic variation produced in sexual life cycles.

7)Draw and Label the stages of Meiosis.

See Pages 254-255 Figure 13.8