# Genetics : Genetics

## Example Questions

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### Example Question #1 : Cell Division

If two genes are found to have a recombination frequency of 25%, what does this mean about the location of the two genes?

The genes are located on the same chromosome and are on opposite ends of the chromosome

The genes are located on the same chromosome and neither extremely close, nor extremely far apart

The genes are linked

The genes are on different chromosomes

The genes are located on the same chromosome and neither extremely close, nor extremely far apart

Explanation:

If the genes were linked, there would be an incredibly small recombination frequency. If the genes were on opposite ends of the chromosome or on separate chromosomes, the recombination frequency would approach the maximum of 50%.

Because the recombination frequency is relatively intermediate, we can conclude that the distance between the genes does not fall at either extreme. The genes are neither very close, nor very far apart.

### Example Question #2 : Genetics

A scientist performs a series of experiments to determine the recombination frequencies between the following genes. He acquires the following data:

W-X: 3%

X-Y: 2%

Y-Z: 13%

Z-W: 8%

Which of the following choices places the genes in the correct order relative to one another?

W, Y, Z, X

W, X, Y, Z

Z, W, X, Y

X, W, Z, Y

Z, W, X, Y

Explanation:

The larger the recombination frequency, the larger the distance between two genes. By looking at the data, we know that genes W and X are close to one another. Also, genes X and Y are close to one another. Gene Z, however, seems to be far away from both W and Y (but closer to W). We can represent these distances relatively in a picture:

W - - - X (3)

X - - Y (2)

Y - - - - - - - - - - - - - Z (13)

Z - - - - - - - - W (8)

The most likely explanation is that W, X, and Y are close to one another and Z is located slightly farther away on whichever side W is closest. A spatial map would look something like this:

Z - - - - - - - - - - W - - - X - - Y

### Example Question #1 : Cell Division

In which phase of cell division does DNA synthesis (replication) occur?

S

G0

S

G1

G2

S

Explanation:

The S phase is the "synthesis" phase, where DNA is duplicated. Cells that are not dividing are considered to be in the G0 phase, however, they can enter the cell cycle if they receive the proper signals. The S phase occurs before the M phase (mitosis) as the cell begins to prepare for division.

### Example Question #1 : Genetics

Which of the following terms is used to described programmed cellular death?

Apoptosis

Heterozygous

Centromere

Allodynia

Homozygous

Apoptosis

Explanation:

Apoptosis is the term used to describe programmed cellular death. Apoptosis is useful because it prevents the replication of damaged/mutated cells. p53 is an important signal that when activated, instructs a cell to commit apoptosis. Cancer is partially caused by a failure of the p53 signal, thus allowing for uninterrupted cellular growth.

### Example Question #2 : Cell Division

In which phase of mitosis do spindle fibers align chromosomes in the middle of the cell nucleus?

Telophase

Prophase

G1

Anaphase

Metaphase

Metaphase

Explanation:

In metaphase, spindle fibers align chromosomes along the middle of the cell nucleus. A good way to remember this is "M" in metaphase stands for middle. In this portion of mitosis, the cell ensures that each daughter cell will receive the appropriate genetic material. Metaphase occurs right before Anaphase.

### Example Question #2 : Genetics

In which phase of the cell cycle does the nucleolus disappear?

Metaphase

Anaphase

Prophase

Telophase

G1 phase

Prophase

Explanation:

The nucleolus disappearing is an important part of the cell cycle. This step takes place in prophase. In prophase, chromosomes become visible under the light microscope. They are visible as the chromatin become condensed. There are important facts to remember about prophase.

### Example Question #1 : Cell Division

Cells arrested from the cell cycle are found in which phase?

G1

M

G0

S

G2

G0

Explanation:

The G0 phase is for cell cycle arrest. Cells in this phase are not actively dividing and are not preparing to divide. Being in G0 is technically "outside" of the cell cycle. A cell must receive certain and specific signals to exit the G0 phase and enter the G1 phase (to prepare for replication and division). Cells within the cell cycle might receive certain signals telling them to stop dividing. in this case, a cell will exit the cell cycle and enter the G0 phase.

### Example Question #3 : Cell Division

During which phase of the cell cycle are the chromosomes replicated through DNA synthesis?

S phase

G2 phase

Cytokinesis

G1 phase

Gphase

S phase

Explanation:

When the cell moves past the restriction point, it has committed to dividing to form a daughter cell. S phase follows immediately after this point, and the cell begins to duplicate all of the chromosomes comprising its genetic material.

### Example Question #2 : Cell Division

Mitosis is the process by which a parent cell divides to produce two daughter cells with identical genetic material. The chromosomes must condense, align, and be pulled apart to complete this process. What is the name of the mitotic phase in which the duplicated sister chromatids are physically pulled apart?

Cytokinesis

Prophase

Telophase

Anaphase

Metaphase

Anaphase

Explanation:

Prophase and metaphase happen before anaphase, and the duplicated chromosomes (sister chromatids) condense and align. During anaphase they are pulled apart and start migrating to opposite cell poles. Telophase and cytokinesis follow anaphase to complete the division of the cell into two new cells.

### Example Question #1 : Genetics

Mitosis is the process by which a parent cell divides to produce two daughter cells with identical genetic material. The chromosomes must condense, align, and be pulled apart to complete this process. What is the name of the protein structure that physically attaches to the chromatids to pull them apart?

Nucleus

Centriole

Mitotic spindle

Centromeres

Allele