Mastering A & P - Lab 20, 21, 22

Homologous chromosomes are labeled __________.

A

The enzyme that synthesizes the new DNA strand during replication is __________.

DNA polymerase (DNA polymerase is an enzyme that works in the nucleus to replicate DNA.)

If the top panel shows the cell before DNA replication and meiosis, then the bottom panel shows the cell in __________.

telophase I

The phase labeled 2 on the figure is the __________.

S phase (The S phase is the phase of interphase in which the DNA is replicated, so when the cell eventually divides, each daughter cell inherits a complete copy of the genome.)

What would happen if a cell completed several rounds of mitosis but did not undergo cytokinesis?

The cell would keep getting larger in size. (Cytokinesis is the fundamental process needed to split the cell into two cells. If this does not occur, the size of the cell would increase in size.)

Synapsis and crossing over takes place during __________.

prophase II of meiosis

Now that you have learned the correct order for the phases of mitosis, this activity will test your understanding of events that occur during each phase. Sort the following events into the phase of mitosis that they occur.

prophase: DNA condenses into chromosomes Nuclear envelope breaks up Centrosomes move to opposite sides of the cell Mitotic spindle fibers form and attach to centromeres Metaphase: Chromosomes align in the center of the cell Anaphase: Sister chromatids separate into chromosomes Chromosomes move along the spindle fibers Telophase: Chromosomes reach the opposite ends of the cell Chromosomes relax and nuclear envelopes form Completion of cytokinesis

Which of the following are tube-shaped organelles that assist in organizing the spindle fibers during mitosis?

centrioles

Two identical copies of the same chromosome are called __________.

sister chromatids

If nondisjunction, a process in which the homologous chromosomes fail to separate, occurs during meiosis I,

the offspring will either have one too many or one too few numbers of chromosomes.

Which of the following is NOT produced by meiosis?

a liver cell

Which of the following is a likely result of meiosis?

four sperm, each with 23 chromosomes

If crossing over and independent assortment ceased to occur,

genetic variation would decline rapidly, with sperm or ova having the same alleles.

The primary sex organs are also called __________.

gonads

During prophase I of meiosis,

homologous chromosomes stick together in pairs.

A cell preparing to undergo meiosis duplicates its chromosomes during

interphase

Chromosomes can exchange genetic information during a process called "crossing over." This occurs when homologous chromosomes are lined up in pairs. When does this happen?

prophase I

During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?

prophase I

The correct order of events during meiosis is

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II.

Rank from the first to the last steps in DNA synthesis.

1.) DNA strands separate as the enzyme helicase unwinds them 2.) The enzyme primase builds RNA primers on the existing DNA strands 3.) DNA polymerase catalyzes the covalent addition of free nucleotides to the growing new DNA strand. 4.) Two identical double helices

The stage of mitosis during which sister chromatids separate and daughter chromosomes are pulled to opposite poles of the cell is called __________.

Anaphase

Which of the following is NOT one of the phases of interphase?

M phase (M phase, or mitosis, is the cell division stage of the cell cycle and follows interphase.)

Which of the following statements about replication is correct? RNA is used as a template to synthesize DNA. Proteins are synthesized during replication. Replication is semiconservative. The main enzyme of replication is RNA polymerase.

Replication is semiconservative. (Replication is semiconservative because the newly formed DNA molecule contains one original DNA strand and one newly synthesized DNA strand.)

Cytokinesis occurs concurrently with what stage of mitosis?

Telophase Cytokinesis, which divides the cytosol and organelles equally between the two daughter cells, occurs at the same time as telophase.

Mitosis produces cells that are ___________; meiosis produces cells that are ___________.

diploid; haploid

When does the total number of chromosomes get reduced from 46 pairs to 23 individual chromosomes?

during meiosis I

After DNA replication, each individual chromosome becomes a homologous pair.

false (After DNA replication, each chromosome is composed of two sister chromatids.)

Meiosis starts with a single diploid cell and produces

four haploid cells.

Both the periwinkle and yew plants produce toxins that interfere with microtubules by binding to them and either inhibiting their assembly (in the case of the periwinkle) or preventing their disassembly (in the case of the yew). Why would both actions ultimately prevent mitosis?

The chromosomes would not be able to line up in the middle and separate the sister chromatids. (Microtubules attach to kinetochores of the chromosomes to line up at the equator and separate the sister chromatids equally in metaphase and anaphase, respectively.)