Chapter 8
A cell biologist carefully measured the quantity of DNA in grasshopper cells growing in cell culture. Cells examined during the G2 phase of the cell cycle contained 200 units of DNA. What would be the amount of DNA in one of the grasshopper daughter cells?
100 units, Recall that G2 follows S, and that during the S phase, DNA is replicated. Then, chromatids are separated during mitosis to form daughter cells.
How many pairs of autosomes do humans have?
22
In humans, the haploid number of chromosomes is 23. Independent assortment has the possibility of producing __________ different gametes.
2^23
A human somatic cell contains __________ chromosomes.
46
Each somatic cell in an individual with Down syndrome contains _____ chromosomes.
47
In a cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing __________ chromosomes.
5
Imagine that a human skin cell went through mitosis but did not undergo cytokinesis. How many chromosomes would be in the cell?
92
Polyploidy is involved in which of the following examples?
A normal watermelon has 22 chromosomes but seedless watermelons have 33 chromosomes.
A benign and a malignant tumor differ in that _____.
cells of a benign tumor remain within the tumor, whereas cells of a malignant tumor can spread to other body tissues
In the picture below, the chromosomal region where the nonsister chromatids are crossing over is called a(n) _____.
chiasma
Meiosis differs from mitosis in that _____ only occurs in meiosis.
crossing over
A cleavage furrow forms in an animal cell during _____
cytokinesis
At the end of the mitotic (M) phase, the cytoplasm divides in a process called _________________.
cytokinesis
Meiosis starts with a single diploid cell and produces
four haploid cells.
During anaphase I, __________.
homologous chromosomes separate and migrate toward opposite poles
Asexual reproduction ___________.
produces offspring genetically identical to the parent
Crossing over occurs during _____.
prophase I
Variation occurs when chromosomes are shuffled in _____.
meiosis
Which of the following indicates Turner syndrome?
XO
Which of the following represents a chromosomally normal human female?
XX
Consider the photograph of a karyotype. This is _____.
a photograph of all a person's chromosomes
Crossing over is important because it __________.
allows the exchange of different versions of genes between homologous chromosomes
If a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction, the resulting chromosomal abnormality is called _____.
an inversion
The stage of mitosis during which the chromosomes move toward separate poles of the cell is _____.
anaphase
In many organisms, including humans, chromosomes are found in homologous pairs. Homologous chromosomes _____.
are identical in the arrangement of their genes, but some versions of the genes may differ between the chromosomes
A cell replicates its entire chromosomal DNA only __________.
before it is about to divide
Which of the following conditions would prevent cell division due to density-dependent factors?
being completely surrounded by other cells
Asexual and sexual reproduction differ in that sexual reproduction _____.
can produce great variation among the offspring
A cell is treated with a drug that prevents the formation of vesicles. Which of the following processes depends on the formation of vesicles and would therefore be blocked?
cytokinesis in a plant cell
In bacterial cells, binary fission involves __________.
distribution of a copy of the single parental chromosome to each daughter cell
The diploid phase of the human life cycle begins with _____.
fertilization
Consider the photograph shown below. You can determine this is a plant cell rather than an animal cell because it has __________.
formed a cell plate
The function of meiosis is to make __________.
four cells with a haploid number of chromosomes
What is the typical result when a diploid cell undergoes meiosis?
four haploid cells
During asexual reproduction, yeast cells can produce _____.
genetically identical offspring
At the conclusion of meiosis I, the daughter cells are _____.
haploid and the sister chromatids are joined
In anaphase I, __________.
homologous chromosomes move toward opposite poles
During prophase I of meiosis,
homologous chromosomes stick together in pairs.
Chromatids are _____.
identical copies of each other if they are part of the same chromosome
A cell preparing to undergo meiosis duplicates its chromosomes during
interphase.
A fragment of chromosome 21 reattaches to chromosome 21, but in the reverse direction. What is the name given to this change?
inversion
When we say that an organism is haploid, we mean that _____.
its cells each have one set of chromosomes
In some organisms such as certain fungi and algae, cells undergo mitosis repeatedly without subsequently undergoing cytokinesis. What would be the consequence of this?
large cells containing many nuclei
Which of the following is a correct representation of an event that occurs in mitosis?
metaphase—chromosomes line up on the equatorial plane.
After fertilization, the resulting zygote begins to divide by __________.
mitosis
During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.
nondisjunction
Down syndrome can be the result of _____.
nondisjunction of chromosome 21 during meiosis
The term binary fission is best applied to _____.
prokaryotes
In the telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in _____.
prophase
Synapsis occurs during _____.
prophase I
The correct order of events during meiosis is
prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II
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.
Which of the following shows mitosis in the correct chronological order? prophase, prometaphase, metaphase, anaphase, telophase telophase, prophase, anaphase, prometaphase, metaphase prometaphase, metaphase, prophase, telophase, anaphase anaphase, prometaphase, metaphase, prophase, telophase
prophase, prometaphase, metaphase, anaphase, telophase
The exchange of parts between nonhomologous chromosomes is called _____.
reciprocal translocation
In meiosis II, _____.
sister chromatids are separated
During anaphase II, __________.
sister chromatids separate and migrate toward opposite poles
The kinetochores are __________.
sites at which microtubules attach to chromosomes
An example of a cell that is 2n is a __________.
somatic cell
DNA replication occurs in _____.
the S phase of interphase
Crossing over is _____.
the exchange of homologous portions of nonsister chromatids
During mitosis, the chromosomes move because _____.
they attach to a dynamic, precisely regulated mitotic spindle
Mitosis and cytokinesis result in the formation of __________; meiosis and cytokinesis result in the formation of __________.
two diploid cells : four haploid cells
At the end of telophase I of meiosis, as cytokinesis occurs, there are __________.
two haploid cells
A human bone marrow cell in the prophase stage of mitosis contains 46 chromosomes. Therefore, there are a total of __________ sister chromatids in this cell.
92, Mitosis follows the S phase, during which the cell's DNA is duplicated.
The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?
Anaphase
What is the difference between a benign tumor and a malignant tumor?
Benign tumors do not metastasize; malignant tumors do
In the laboratory, cancer cells fail to show density-dependent inhibition of growth in cell culture. What is one explanation that could account for this?
Cancer cells continuously secrete growth factors into the cell culture medium.
During meiosis I, homologous chromosomes form a tetrad and crossing over occurs. What is the outcome of crossing over?
Crossing over creates new combinations of genes present on a single chromosome
Which of the following statements correctly describes the timing of DNA synthesis?
DNA is synthesized in the S phase of interphase.
Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?
Extra copies of the other somatic chromosomes are probably fatal.
Cells will usually divide if they receive the proper signal at a checkpoint in the __________ phase of the cell cycle.
G1
Immune system cells enter a resting phase after undergoing mitosis. When activated—for example, by an infection—they can reenter the sequence of events in the cell cycle that leads to cell division. What would be the correct cell cycle sequence of events for these reactivated cells?
G1, S, G2, M
When examining cells in the laboratory, you notice that a particular cell has half as much DNA as the surrounding cells. This observation can be explained if this cell's cell cycle halted at checkpoint _____.
G1, The cell cycle must have stopped before the S phase; otherwise, the cell would also have twice as much DNA
You suspect that a serious developmental disorder is due to a chromosome abnormality and prepare a karyotype from an affected individual. In analyzing the karyotype, how could you distinguish trisomy from a chromosome structural defect such as a duplication?
In trisomy there would be one extra chromosome; in a duplication, the number of chromosomes would be normal, but one chromosome would have two copies of a portion of the chromosome.
During binary fission, each copy of the duplicating chromosome moves to opposite ends of the cell. What does this achieve?
It ensures that each daughter cell receives one copy of the chromosome.
The chromosomes line up in the center of the cell during which phase of mitosis?
Metaphase
Trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the X chromosome is not. What is the explanation for this difference?
Only one copy of the X chromosome is functional within any given cell, regardless of the total number of X chromosomes.
The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?
Prophase
Which of the following is a key difference between meiosis and mitosis?
Synapsis occurs.
The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis?
Telophase
The sequences are identical.
The chromosomes must be duplicated.
What would be the immediate consequence of destroying a cell's centrosomes?
The mitotic spindle would not form.
The M phase of mitosis and M phase of meiosis both occur after interphase. However, the two processes differ in the arrangement and behavior of their chromosomes. How?
The pairing up of homologous chromosomes and crossing over only occur during meiosis.
Within one chromosome, what is the relationship between the sequence of bases in DNA of one sister chromatid compared to the other?
The sequences are identical.
During cell division, what role do centrosomes play?
They organize the microtubules.
Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. Of the remaining 19 autosomes, many trisomies have not been seen in newborns. Why not?
Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried.
Which of the following occurs during mitosis?
Two daughter nuclei, one at each pole of the cell, are generated.
In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?
Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.