15 & 16 Mitosis and Meiosis

A skin cell in G2 of interphase has _____ as much DNA as it had in G1.

Twice (S phase, where DNA synthesis occurs, and the chromosomes are all replicated, is in between G1and G2phases of the cell cycle)

The FoxP2 gene is thought to be involved in language in humans. At prophase I, how many copies of the FoxP2 gene are present in a cell? Keep in mind that humans are diploid.

4 copies; 1 on each sister chromatid in a pair of homologous chromosomes

The random alignment of maternal and paternal homologous chromosomes during metaphase I is one of the ways genetic variability among gametes comes about. For example, it is possible for an organism with 4 pairs of homologous chromosomes to produce gametes with up to 16 different combinations of maternal and paternal chromosomes (24= 16). In the case of humans with 23 pairs of chromosomes, there are over 8 million possible combinations. How many possible combinations of maternal and paternal chromosomes are possible in the gametes of an organism with 6 chromosomes?

64 - There are two options for each chromosome, maternal and paternal, and the two options can occur six times: 26 options for 64 total possibilities.

What type of protein is being activated by the G1/S cyclin-CDK complex to promote the expression of histone genes?

A transcription factor (Recall that the regulation of gene expression involves the binding of transcription factors to stimulate RNA polymerase transcription)

At which checkpoint would a cell become arrested if a chromosome was not properly aligned in the spindle?

At a checkpoint early in the mitotic phase (The M phase checkpoint is dependent on signals associated with spindle fiber attachment to kinetochores on the chromatids. Only after attachment of every last kinetochore will the cell progress from metaphase to anaphase)

Why does meiosis result in more genetic variation than can be explained by mutation alone? Select all that apply.

Because of the random alignment of maternal and paternal homologs during metaphase of meiosis I Because of crossing over between homologs during prophase I

How does meiosis generate genetic diversity?

Both crossing over at prophase I and random alignment of homologs at metaphase I (Genetic diversity is from the sequence differences that differ on the homologs derived from each parent. The way those slightly different chromosomes are mixed and then divided up to form gametes is the process that generates genetic diversity in each gamete. It is enhanced by the fact that homologs undergo recombination in Meiosis I, so the homologs are also mixed up.)

What cellular process(es) is/are responsible for the increase in protein content associated with the gap phases of the cell cycle?

Both transcription and translation (Increased protein content comes most directly from translation, but translation requires RNA produced from transcription, so both are required)

A graduate student is planning an experiment to evaluate the expression of PDGF-related genes in her cell population of interest. As a control, she hopes to confirm the expression of genes that are present in all dividing cells. For her controls, she should evaluate the expression of:

CDKs

Which choices accurately match each of the cellular processes to the stage of meiosis in which it occurs? Select all that apply.

Chromosomes condense to thickened structures that are visible under the microscope in prophase I. Microtubules attach to kinetochores at the centromere of each homolog in prometaphase I. The nuclear envelope disappears in prophase I.

Predict what would happen if crossing over between homologous chromosomes occurred as part of mitosis.

Daughter cells would not be genetically identical. (Somatic cells undergo mitosis, and they have genetic diversity because they have copies of each chromosome from two parents, who were genetically different. If crossing over occurred in mitosis, the resulting cells could end up with copies of parts of chromosomes that both came from the same parent, and that would differ from the other daughter cell formed in that unusual mitosis.)

When nutrients are suboptimal for cell growth and division, the cell cycle arrests. At which stage of the cell cycle/checkpoint would you predict this arrest to occur?

G1 checkpoint

Which one of the statements regarding the S cyclin-CDK complex is true?

It ensures that DNA is not replicated multiple times.

The alignment of chromosomes at metaphase of meiosis II is most similar to the alignment of chromosomes during metaphase of mitosis.

True

Which of the options correctly match the type of cell division with the cellular events or results characteristic of that type of cell division? Select all that apply.

Mitosis produces genetically identical daughter cells. In meiosis, the original cell undergoes two rounds of cell division. Meiosis produces genetically unique daughter cells.

A researcher is studying phases of the cell cycle in a population of cells during which there is an increase in the DNA content. This stage is most likely:

S Phase

The second meiotic division resembles mitosis because:

Spindle microtubules attach from opposite directions to the centromere of each sister chromatid pair. The daughter cells have the same number of chromosomes as the parent cell. Sister chromatids are separated during anaphase II to become the chromosomes of the daughter cells.chromosomes decondense during telophase II. The second meiotic division is much like mitosis except it is starting with half the number of chromosomes after the reduction division in meiosis I. Spindles form to facilitate the separation of sister chromatids, which decondense after telophase.

A researcher is evaluating the expression of p53 in cells she is culturing in the laboratory. She notices that in a small group of cells, high levels of phosphorylated p53 occur in the nuclei. What can she deduce about these cells?

These cells likely contain damaged DNA. (Damage to the DNA can occur in any stage of the cell cycle and when it occurs, p53 is phosphorylated and transported into the nucleus where it participates in stopping the cell cycle and activating the DNA repair process)

Non-sister chromatids are:

copies of homologs but not fully identical chromosomes.

The amount of _____ is fairly constant throughout the cell cycle, but the amount of _____ varies.

cyclin-dependent kinases; cyclins (Cyclin levels rise and fall during the cell cycle, but cyclin-dependent kinase (CDK) levels remain constant. The activity of CDKs does increase though when cyclin levels are high, causing cyclins to bind and activate CDKs.)

Which stages of mitosis are correctly matched with the events that occur in the stage? Select all that apply.

cytokinesis; a contractile ring of actin filaments forms at the cell equator metaphase; chromosomes line up in the middle of the cell

Prophase of meiosis I has some important differences from prophase of mitosis. These differences include: ___________ pair, and _________ occurs.

homologous chromosomes; crossing over

Homologous chromosomes separate from each other in:

meiosis I

During meiosis, genetic variability is introduced during which phase?

metaphase I

Many of the specific functions that are triggered when a cell passes one of the cell cycle checkpoints result from activation of enzymes and other proteins. A common mechanism for this activation is:

phosphorylation of specific proteins.

Why would a compound that interferes with bacterial cell wall synthesis be useful for treating a bacterial infection?

t would limit growth of the bacterial population through cell division. (When bacterial cells grow and divide by binary fission, they must construct new cell walls. Blocking the synthesis of cell walls would slow or block bacterial growth)

Which of these events includes a checkpoint in the cell cycle?

the transition from G1 to S phase

Meiosis is thought to have appeared early in evolution because most eukaryotes perform meiosis and the steps of meiosis are the same in all eukaryotes.

true