Chapter 8
A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.
16
Normal human gametes carry _____ chromosomes.
23
How many spindle poles is each condensed chromosome attached in metaphase?
2; Each chromosome is attached to two spindle poles in metaphase.
Which would be more severe? A mitotic error producing aneuploid cells in the second division of a fertilized egg; or a mitotic error producing aneuploid cells in the 20th division of a fertilized egg?
2nd division because this could cause HALF of the organism's cells to be aneuploid, as all of these cell's descendants would be aneuploid as well.
Human cells have 46 condensed chromosomes at the start of mitosis. How many sister chromatids are passed on to each daughter cell?
46; Each daughter cell receives one sister chromatid from each chromosome.
Human cells have 46 condensed chromosomes at the start of mitosis. How many DNA molecules are in a cell at the start of mitosis?
92
asexual reproduction
A reproductive process that involves only one parent and produces offspring that are identical to the parent.
In which phases of mitosis is the nuclear envelope absent for at least part of the phase?
All but Prophase
Which phases are chromatids or sister chromosomes connected to the spindle?
All but Prophase
During _____ sister chromatids separate.
Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.
Why is there a checkpoint at the end of metaphase instead of during anaphase or later?
Anaphase is irreversible. Once it is triggered, cohesin dissolves and sister chromatids separate from each other.
Meiosis I produces _____ cells, each of which is _____.
At the end of meiosis I there are two haploid cells.
Meiosis II typically produces _____ cells, each of which is _____.
At the end of meiosis II there are typically 4 haploid cells.
At the end of _____ and cytokinesis there are four haploid cells.
At the end of telophase II and cytokinesis there are four haploid cells.
During prophase a homologous pair of chromosomes consists of _____.
At this point each of the chromosomes consists of two chromatids.
Spindle fibers attach to kinetochores during _____.
Attachment of spindle fibers to kinetochores is one of the events of prometaphase.
What must happen before a cell can begin mitosis?
Before mitosis can begin, the chromosomes, or genetic material, must be copied, which occurs during interphase.
A cell preparing to undergo meiosis duplicates its chromosomes during
Chromosomes are duplicated during interphase.
_________ is a protein complex that holds sister chromatids together from the time DNA replicates until chromatids separate during mitosis.
Cohesin
At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.
Correct At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.
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.
At the end of the mitotic (M) phase, the cytoplasm divides in a process called _________________.
Cytokinesis is the division of the cytoplasm that occurs in conjunction with telophase, the last phase in mitosis.
Cytokinesis often, but not always, accompanies _____.
Cytokinesis often, but not always, accompanies telophase.
Homologous chromosomes migrate to opposite poles during _____.
During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.
How do microtubules behave differently during anaphase?
During anaphase, a sister chromatid remains attached to a microtubule in the absence of something pulling in the opposite direction.
Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
During anaphase, sister chromatids separate and migrate to opposite poles.
Chromosomes become visible during _____.
During prophase, the chromatin fibers become discrete chromosomes.
Why do chromosomes move to the midline when attached to both spindle poles?
Each pulls on the chromosome in a tug-of-war that moves the chromosome to the middle.
True or False; The spindle attaches to cohesin during prometaphase.
False
The spindle assembly checkpoint ________.
Helps prevent Aneuploidy.
During prophase I of meiosis...
Homologous chromosomes stick together in pairs during prophase I.
During _____ the cell grows and replicates both its organelles and its chromosomes.
Interphase
__________ is the only time that chromosomes line up by homologous pairs.
Meiosis I
Meiosis starts with a single diploid cell and produces
Meiosis produces four haploid cells.
The correct order of events during meiosis is....
Meiosis starts with prophase I and continues with metaphase I, anaphase I, telophase I, and cytokinesis. This is followed by meiosis II.
During _____ chromosomes align single file along the equator of a haploid cell.
Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.
The chromosomes line up in the center of the cell during which phase of mitosis?
Metaphase occurs in the middle of mitosis, when the chromosomes line up in the middle of the cell.
_________ goes on continuously in most parts of the body, whereas meiosis takes place only in the gonads.
Mitosis
Nucleoli are present during _____.
Nucleoli are present during interphase.
Which phase of mitosis is arrested by the cancer drug Taxol?
Prometaphase; the spindle does not properly attach to chromosomes.
During _____ a spindle forms in a haploid cell.
Prophase II is essentially the same as mitotic prophase except that the cells are haploid.
The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?
Prophase is the first phase of mitosis, when the centrosomes begin moving toward opposite poles and the nuclear envelope breaks up.
During meiosis, segments of non-sister 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?
Segments of nonsister chromatids trade places during prophase I, resulting in recombination.
endoreplication
Set of chromosomes replicates repeatedly without nuclear division. Cytokinesis is absent from the cell cycle.
The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?
Sister chromatids separate and start their migration toward opposite poles during anaphase.
In meiosis II, _____.
Sister chromatids separate. This is the task of meiosis II and is the reason meiosis II resembles mitosis.
An example of a cell that is 2n is a __________.
Somatic cell; Somatic is a word used to refer to the "body." These body cells are diploid and have two homologous copies of each chromosome.
Synapsis occurs during _____.
Synapsis, the pairing of homologous chromosomes, occurs during prophase I.
The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis?
Telophase is the final phase of mitosis, when the chromosomes have arrived at the poles and the nuclear envelopes of the two new cells form.
________________is the point of attachment between two duplicated chromosomes.
The centromere
Why do cells coil DNA into condensed chromosomes?
The coiled structure facilitates movement of DNA molecules in the cell.
Why does the nuclear envelope dissolve during mitosis?
The nuclear envelope is impenetrable to the spindle in many organisms, and would block proper movement of chromosomes during mitosis. However, the spindle can (and does) form when the nuclear envelope is present.
embryonic development
The process by which the embryo is formed and develops, until it develops into a fetus.
In which way does the spindle move attached chromosomes?
The spindle pulls the chromosomes toward a spindle pole center. The spindle can only pull-it cannot push chromosomes.
The diploid phase of the human life cycle begins with _____.
The union of haploid gametes at fertilization produces the zygote, or fertilized egg, which starts the diploid phase of the life cycle of humans and is characteristic of animals.
What can microtubules attach to?
They attach at one end to centrosomes and the other to kinetochore.
True of False; Sister chromatids in the same chromosome have equivalent DNA and are connected by cohesin.
True
True of false; DNA is in its condensed form during every phase of mitosis?
True
True or False; During anaphase, sister chromatids are pulled by motor proteins that are attached to microtubules.
True
Without ________ tension can never devlope at the attachment, so the microtubules release.
cohesin
Just before mitosis, the chromosomes in a body cell are ______________, but the sister chromatids remain joined together. So you will see ___________chromosomes in a typical body cell.
duplicated; double
recombinant gametes
gametes with new combinations of alleles
Once meiosis I is completed, cells are _______.
haploid
Gametes are produces by
meiosis
We can see that the chromosomes are duplicated and lined up by homologous pair. That only happens at the start of ___________.
meiosis I.
Spindles in all eukaryotic cells have a protein complex called the ______________.
microtubule organizing center
Problems with cohesin would result in ___________.
premature separation of some of the chromosomes.
Which processes lead to most genetic variation in sexually reproducing organisms?
random fertilization, independent orientation of chromosomes in meiosis, crossing over
During _____ both the contents of the nucleus and the cytoplasm are divided.
the mitotic phase (encompasses both mitosis and cytokinesis)