Unit 4 (Week 12 Mitosis and Meiosis) Flashcards
[16.1 Start - The Eukaryotic Cell Cycle] What is the process of cell reproduction, in which one cell splits into two cells?
Cell division
What is a series of events that leads to cell division. For eukaryotes, it involves a series of phases in which a cell divides by mitosis or meiosis?
Cell cycle
What is the field of genetics that involves the microscopic examination of chromosomes?
Cytogenetics
When a cell prepares to divide, and the chromosomes become tightly compacted, their length decreases but their diameter increases. What results from this?
A consequence of this compaction is that distinctive shapes and numbers of chromosomes become visible under a light microscope.
Researchers usually treat cells with drugs that stimulate them to divide before beginning the procedure for making a karyotype. Why is this treatment useful?
Chromosomes are readily seen when they are compacted in a dividing cell. By adding such a drug, the researchers increase the percentage of cells that are actively dividing.
What is a an individual’s collection of chromosomes? Also, useful technique in laboratories to photograph and analyze chromosome structure and possible abnormal numbers.
Karyotype.
A photographic representation of the chromosomes from an actively dividing cell. A karyotype reveals the number, size, and form of chromosomes found within an actively dividing cell.
T/F Chromosomes viewed in a karyotype of an actively dividing cell have already been replicated.
True.
What are the two duplicated chromatids that are still joined to each other after DNA replication?
Sister chromatids
How many sets of chromosomes does one set of HUMAN chromosomes have?
23 different types of chromosomes
What does the numbering system of chromosomes not apply to?
The 23rd chromosome, which is the sex chromosomes, which determine the sex of the individual.
What are the letters that determine the sex chromosomes of whether or not a human is male or female?
XX and XY.
Females are XX and males are XY.
What are all of the chromosomes found in the cell nucleus of eukaryotes except for the sex chromosomes?
Autosomes. 22 different types
T/F Many eukaryotic species have cells that contain two sets of chromosomes, with 23 different chromosomes in each set.
True.
Therefore, this human cell contains a total of 46 chromosomes.
Why do most eukaryotic species have two sets of chromosomes?
One inherited by the mother and one inherited by the father.
What do you call a cell containing two sets of chromosomes; designated as 2n?
A diploid.
Since humans are 2n, where n = 23. 23 x 2 = 46
What is the haploid cell that is involved with sexual reproduction, such as a sperm or egg cell?
Gamete
What is a 1n cell, which means they contain one set of chromosomes?
Haploid. These are what gametes are considered as.
What is the member of a pair of chromosomes in a diploid organism?
A homolog.
1 chromosome and the other chromosome, within a pair, are homologous of each other.
Homologous = similar in position, structure, and evolutionary origin but not necessarily in function.
What is a similarity that occurs due to descent from a common ancestor?
Homology
The OCA2 gene found in chromosome 15 determines eye color. Do each homolog confer the same color?
Not always. Since 1 is received from each parent, one may confer blue while the other will confer brown.
What is typically the difference between two chromosomes from different parents, like for example, chromosome 1?
Less than 1% in differences.
What chromosomes does homology, even with slight similarities, not apply and they differ in size and genetic composition?
The sex chromosomes - XX and XY.
Certain genes found on the X chromosome are not found on the Y chromosome, and vice versa. The X and Y chromosomes are not considered homologous chromosomes, although they do have short regions of homology.
What types of changes occur in eukaryotic cell division?
Growth, replication, and division.
What are the phases of cell division?
G1, S, G2, and M.
What is produced at the end of cell division?
Two daughter cells.
During the S phase of cell division, what happens to the count of individual or set chromosomes?
It doubles.
For example, the cell dividing has 3 sets (6 individual chromosomes) and in the S phase, they are replicated to equal 12 individual chromosomes or 6 sets.
This replication creates Chromatids!!!
Which phase, during cell division, is the shortest and which is typically the longest?
M phase is the shortest while G1 is the longest phase.
Which phases make up interphase?
Interphase consists of the G1, S, and G2 phases of the cell cycle.
The portion of the cell cycle consisting of the G1, S, and G2 phases, during which the chromosomes are decondensed and found in the nucleus.
List the phases of cell division in order and what their abbreviations mean.
G1 which is the first gap
S which is the synthesis of DNA, the genetic material.
G2 which is the second gap
M which is the phase of mitosis and cytokinesis
What were G1 and G2 phases originally described to indicate what?
Gaps in the DNA synthesis and mitosis phases.
What phase does the cell grow and copy its chromosomes in preparation for cell division?
The interphase
What phase happens when a cell exits the cell cycle and remain for long periods of time? This is an alternative to proceeding through G1.
G0 or G zero phase.
A cell in the G0 phase has postponed division or, in the case of terminally differentiated cells (such as muscle cells in an adult animal), will never divide again. G0 is a nondividing phase.
What phase in the cell cycle pertains to cell growth and the commitment of division? Typically triggered by environmental conditions and signaling molecules.
G1 Phase
In what phase does each chromosome replicate to form a pair of sister chromatids? At the conclusion of this cycle, a cell will have twice as many chromatids as the number of chromosomes in the previous phase.
S phase.
For example, a human cell in G1 phase has 46 distinct chromosomes, whereas the same cell in G2 phase will have 46 pairs of sister chromatids, for a total of 92 chromatids.
[Bonus] When do we use the phrase sister chromatid?
Term sister chromatid is only used during the parts of cell division when the structures are in that X shape, or when the two copies are connected by a centromere.
What phase is when a cell synthesizes the proteins necessary for chromosome sorting and cell division? Some cell growth may occur.
G2 phase
In eukaryotes, what is the phase in the process in which nuclear division results in two nuclei, each of which receives the same complement of chromosomes?
Mitosis
What follows mitosis, in which the division of cytoplasm produces two distinct daughter cells?
Cytokinesis
T/F Cell division can vary where embryos divide in a few minutes while slow-growing adult cells divide in several months.
True.
For a cell that divides in 24 hours, what is the time it takes for each phase to finish? Think 3-4-3 gaps
G1 phase: 11 hours
S phase: 8 hours
G2 phase: 4 hours
M phase: 1 hour
Again, what triggers cell division? (3)
External factors such as environmental conditions and signaling molecules.
Growth factors have an effect as well on cell division (see picture)
What internal factors effect cell division? (2)
Cell cycle control molecules and checkpoints.
Why is the advancement through the cell cycle highly regulated?
To ensure that the genome remains intact and that the conditions are appropriate for the cell to divide.
What are responsible for advancing a cell through the phases of the cell cycle?
Cyclins - A protein responsible for advancing a cell through the phases of the cell cycle by binding to a cyclin-dependent kinase.
Cyclin-dependent kinases (cdks) - A protein responsible for advancing a cell through the phases of the cell cycle. Its function is dependent on the binding of a cyclin.
To be active, the cyclin-dependent kinases controlling the cell cycle must bind to (are dependent on) cyclins. The numbers of different types of cyclins and cdks vary from species to species.
Why are cyclins named the way they are?
Cyclins are so named because their amount varies throughout the cell cycle.
Cyclin/cdk complexes are needed to transition a cell through the cell division cycle. What is the significance of these complexes, like G1 cyclin/cdk and mitotic cyclin/cdk?
For G1 complex, it increases the nutrients and growth factors. For mitotic complex, it allows for the phosphorylation of proteins needed in the M phase.
Once these complexes complete their jobs, they are degraded and the products are reused at a later time.
How many critical regulatory points called checkpoints are found in the cell cycle of eukaryotes?
Three
At these checkpoints, a variety of proteins act as sensors to determine if a cell is in the proper condition to divide.
Which checkpoint determines if conditions are favorable for division which commits for division and senses if DNA has incurred damage?
The restriction checkpoint in the G1 phase. This checkpoint can prevent complexes from being formed.
Where is the second checkpoint located that also checks for DNA damage and ensures all DNA has been replicated? This checkpoint’s proteins also monitor the levels of proteins that are needed to advance through the M phase,
In the G2 phase known as the G2 checkpoint
What is the metaphase checkpoint accomplish? (2)
- Proteins that monitor the integrity of the spindle apparatus (involved in chromosome sorting)
- Checks to see if all chromosomes are attached to the spindle during mitosis
Main purpose of checkpoint proteins in cell division?
A primary aim of checkpoint proteins is to prevent the division of a cell that has incurred DNA damage or harbors abnormalities in chromosome number.
[Bonus] What today is the maturation-promoting factor or MPF that was discovered in leopard frogs when Masui and Markert speculated about the protein triggers in cell division?
Cyclin and cyclin-dependent kinases (cdks)!
[Start 16.2 Mitotic Cell Division] What is a process whereby a eukaryotic cell divides to produce two new cells that are genetically identical to the original cell?
Mitotic Cell Division
What two specific processes does mitotic cell division involve?
Mitosis and cytokinesis
What is a reproductive strategy that occurs when offspring are produced from a single parent, without the fusion of gametes from two parents? The offspring are therefore clones of the parent.
Asexual reproduction
What are two examples of organisms that asexually reproduce?
Baker’s yeast (Saccharomyces cerevisiae) and the amoeba
Other than understanding asexual reproduction, why else is mitotic cell division important?
A second important reason for mitotic cell division is the production and maintenance of multicellularity. Organisms such as plants, animals, and most fungi are derived from a single cell that subsequently undergoes repeated cell divisions to become a multicellular organism.
What is a laymen way of understanding a pair of sister chromatids?
When DNA is replicated, two identical copies of the original double helix are produced.
These copies, along with associated proteins, lie side-by-side are termed sister chromatids.
Essentially, its two strands of replicated DNA attached by a centromere.
Why are sister chromatids easy to see under a light microscope when prepping for cell division?
The heavy compaction increases their width!
What is the region where the two sister chromatids are tightly associated; this is an attachment site for kinetochore proteins?
Bonus Q: What is the protein that holds the sister chromatids together?
Centromere; Cohesin.
Additionally, what does the centromere also act as and for what?
An attachment site for a group of proteins that form the kinetochore.
This is necessary for sorting chromosomes.
What is the structure responsible for organizing and sorting the chromosomes during mitosis?
Mitotic spindle. Also called the mitotic spindle apparatus.
What is the mitotic spindle composed of?
Microtubules.
Where does the microtubules in the mitotic spindle apparatus start to grow?
The microtubule growth and organization starts at two centrosomes, also referred as microtubule-organizing centers (MTOCs)
[Focus Mitotic Spindle Growth]
- In what phase does a single centrosome duplicate?
- What is defined by the centrosomes when entering mitosis?
- What do animal cells have that plant cells do not which consists of a pair with the centrosome and each one has nine sets of triplet microtubules?
- What organizes the construction of microtubules using what proteins?
- What are the three types of spindle microtubules formed in animal cells during cell division cycle?
- Lastly, where are these microtubules located during cell division?
- The interphase
- Two poles; one within each daughter cell.
- Centrioles. These are not required in plants for spindle formation.
- Centrosomes by rapidly polymerizing tubulin proteins.
- Astral, polar, and kinetochore microtubules.
- Astral microtubules emanate away from the region between the poles. Polar microtubules project into the region between the poles. The kinetochore microtubules are attached to the sister chromatids.
What is the sorting process for dividing one cell nucleus into two nuclei?
Mitosis
What are the functions of the three types of microtubules?
The astral microtubules, which extend away from the chromosomes, are important for positioning the spindle apparatus within the cell. The polar microtubules project into the region between the two poles. Polar microtubules that overlap with each other play a role in the separation of the two poles. Kinetochore microtubules are attached to kinetochores at the centromeres and are involved in sorting the chromosomes.
Aside from interphase (which you have already learned), what phases consists of the continuum of phases for mitosis? There are 5 sub phases.
Prophase, prometaphase, metaphase, anaphase, and telophase
What happens in the prophase?
Sister chromatids condense into highly compacted structures which are visible in light microscopy. As this phase proceeds, the nuclear envelope begins to dissociate into small vesicles and the nucleolus is no longer visible.
What phase has the nuclear envelope entirely dissociated into vesicles, and the mitotic spindle is fully formed?
The centrosomes also moves apart and demarcate the two poles. At this point, the spindle fibers can interact with the sister chromatids.
The prometaphase.
The sister chromatids can actually be seen under a microscope undergoing jerking motions as they are tugged, back and forth, between the two poles by the kinetochore microtubules.
In what phase are the pairs of sister chromatids aligned in a single row along the metaphase plate, a plane halfway between the two poles of the spindle apparatus?
The metaphase. When this alignment is complete, the cell is in metaphase of mitosis. The chromatids can then be equally distributed into two daughter cells.
What happens during the anaphase? (3)
- Connections between the pairs of sister chromatids are broken which become individual chromosomes.
- The individual chromosomes are linked to one or two poles by one or more kinetochore microtubules.
- The kinetochore microtubules shorten, pulling chromosomes toward respective poles while the two poles move farther away from each other.
During which phase has the chromosomes reached their respective poles and decondense?
The nuclear envelope now re-forms to produce two separate nuclei.
The telophase
T/F Mitosis is very different between animals and plants while cytokinesis is very similar.
False. Mitosis is very similar in plants and animals. Cytokinesis is quite different, though.
What are the similarities and differences between animal and plant cells with regard to cytokinesis?
Cytokinesis in both animal and plant cells follows mitosis and separates a mother cell into two daughter cells. In animal cells, cytokinesis involves the formation of a cleavage furrow, which constricts like a drawstring to separate the cells. In plants, the two daughter cells are separated by a cell plate, which forms a cell wall between them.
[Start 16.3 Meiosis]
What is the process by which haploid cells are produced from a cell that was originally diploid?
Meiosis
For example, a diploid human cell contains 46 chromosomes, but a human gamete—sperm or egg cell—is a haploid cell that contains only 23 chromosomes.
What are the two rounds of division needed for diploid cells to become gametes?
Meiosis I and Meiosis II
What phases must happen before meiosis begins?
G1, S, and G2 phase.
What are the two events that occur in the beginning of meiosis that do not occur in mitosis?
- Homologous pairs of sister chromatids associate with each other, lying side by side to form a bivalent AKA a tetrad.
- A process called crossing over which is the exchange of genetic material between homologous chromosomes during meiosis; allows for increased variation in the genetic information that each parent may pass to the offspring.
What does crossing over in meiosis accomplish?
Crossing over increases the genetic variation of sexually reproducing species.
What is the process called in which the forming of the bivalent AKA tetrad occurs?
Synapsis
In most eukaryotic species, a protein structure called the synaptonemal complex connects homologous chromosomes during a portion of meiosis. However, the synaptonemal complex is not required for the pairing of homologous chromosomes because some species of fungi completely lack such a complex, yet their chromosomes associate with each other correctly.
During crossing over, what is the connection made at the cross over site between the two pairs of chromatids?
The chiasma (plural = Chiasmata)
This formation resembles an x as the Greek letter chi
After chromosomes are replicated in the S phase, what sequential divisions follow?
Meiosis I and Meiosis II
T/F Meiosis I and Meiosis II also go through a continuum of phases called the prophase, prometaphase, metaphase, anaphase, and telophase.
True
What does the sorting in meiosis I do to the homologous chromosomes?
Separates them
[Focus Meiosis I]
- What is the difference between Prophase I and Prophase in mitosis?
- What is the key difference between Prometaphase I in meiosis and prometaphase in mitosis?
- How is the alignment different in meiosis than mitosis of the sister chromatids?
- What is significant about the organization of sister chromatids in the double row during Metaphase I?
- Separation to poles occurs in the phase, but in meiosis, the sister chromatids remain together?
- What is another name for Telophase I, where the two nuclei are produced, the product of are considered haploid because they do not have homologous chromosomes?
- Bivalent is formed and crossing over occurs in Meiosis I.
- Instead of the pairs of sister chromatids being attached to both poles, they are only attached to 1 pole in MI (Meiosis I).
- They are in a double row rather than a single row.
- Maternal and paternal homologs are randomly aligned along the metaphase plate. Random alignments = 2^n.
- Anaphase I
- Reduction division… They are not homologous because of the cross over of information.
[Information: Emphasis on the Random alignment of sister chromatids]
The possible number of different, random alignments equals 2n, where n equals the number of chromosomes per set. The reason why the random alignments equals 2n is because each chromosome is found in a homologous pair and each member of the pair can align on either side of the metaphase plate. It is a matter of chance which daughter cell of meiosis I will get the maternal chromosome of a homologous pair, and which will get the paternal chromosome.
In humans, who have 23 chromosomes per set, 2n equals 223, or over 8 million possibilities. Because the homologs are genetically similar but not identical, we see from this calculation that the random alignment of homologous chromosomes provides a mechanism to promote a vast amount of genetic diversity among the resulting haploid cells. When meiosis is complete, any two human gametes are extremely unlikely to have the same combination of homologous chromosomes.
None
What is Meiosis I followed by?
Cytokinesis and Meiosis II
What is the main differences between mitosis and meiosis II?
The starting point.
For a diploid cell with six chromosomes, mitosis begins with 12 chromatids that are joined as six pairs of sister chromatids.
By comparison, the two cells that begin meiosis II each have six chromatids that are joined as three pairs of sister chromatids. Otherwise, the steps that occur during prophase, prometaphase, metaphase, anaphase, and telophase of meiosis II are analogous to a mitotic division.
[Focus Difference of Mitosis and Meiosis]
Mitosis produces two diploid daughter cells that are genetically identical.
Meiosis reduces the number of sets of chromosomes. The starting cell also had six chromosomes, whereas the resulting four daughter cells have only three chromosomes.
However, the daughter cells do not contain a random mix of three chromosomes. Each haploid daughter cell contains one complete set of chromosomes, whereas the original diploid mother cell had two complete sets.
DNA replication occurs prior to mitosis and meiosis I, but not between meiosis I and II. During prophase of meiosis I, the homologs synapse to form bivalents. This explains why crossing over occurs commonly during meiosis, but rarely during mitosis. During prometaphase of mitosis and meiosis II, pairs of sister chromatids are attached to both poles. In contrast, during meiosis I, each pair of sister chromatids (within a bivalent) is attached to a single pole. Bivalents align along the metaphase plate during metaphase of meiosis I, whereas sister chromatids align along the metaphase plate during metaphase of mitosis and meiosis II. At anaphase of meiosis I, the homologous chromosomes separate, but the sister chromatids remain together. In contrast, sister chromatid separation occurs during anaphase of mitosis and meiosis II. Taken together, the steps of mitosis produce two diploid cells that are genetically identical, whereas the steps of meiosis involve two sequential cell divisions that produce four haploid cells that may not be genetically identical.
DNA replication:
Occurs prior to mitosis
Occurs prior to meiosis I
Does not occur between meiosis I and II
Synapsis during prophase:
No
Yes, bivalents are formed.
No
Crossing over during prophase:
Rarely
Commonly
Rarely
Attachment to poles at prometaphase:
A pair of sister chromatids is attached to kinetochore microtubules from both poles.
A pair of sister chromatids is attached to kinetochore microtubules from just one pole.
A pair of sister chromatids is attached to kinetochore microtubules from both poles.
Alignment along the metaphase plate:
Sister chromatids align.
Bivalents align.
Sister chromatids align.
Type of separation at anaphase:
Sister chromatids separate. A single chromatid, now called a chromosome, moves to each pole.
Homologous chromosomes separate. A pair of sister chromatids moves to each pole.
Sister chromatids separate. A single chromatid, now called a chromosome, moves to each pole.
End result when the mother cell is diploid:
Two daughter cells that are diploid
—
Four daughter cells that are haploid
[16.4 Sexual Reproduction Start]
What is the process in which two haploid gametes unite in a fertilization event to form a diploid cell called a zygote?
Sexual reproduction
For multicellular species such as animals and plants, the zygote then grows and divides by mitotic cell divisions into a multicellular organism with many diploid cells.
What is the sequence of events that characterize the steps of development of the individuals of a given species?
Life cycle
What is the main purpose of meiosis in animals? What is the main purpose of mitosis in animals?
The purpose of meiosis in animals is to produce gametes. These gametes combine during fertilization to produce a diploid organism. Following fertilization, the purpose of mitosis is to produce a multicellular organism.
What are species in which the diploid organism is the multicellular organism in the life cycle. Animals are an example.
Diploid-dominant species
What are species in which the haploid organism is the multicellular organism in the life cycle. Examples include fungi and some protists.
Haploid-dominant species
What is the phenomenon that occurs in plants and some protists in which the life cycle alternates between multicellular diploid organisms, called sporophytes, and multicellular haploid organisms, called gametophytes?
Alternation of generations
[16.5 Start Variation in Chromosome Structure and Number]
Why is the study of chromosomal variation important? (2)
- Geneticists have discovered that variations in chromosome structure and number can have major effects on the characteristics of an organism. We now know that several human genetic diseases are caused by such changes.
- Changes in chromosome structure and number have been an important factor in the evolution of new species.
T/F Chromosome composition within a given species tends to remain relatively constant. In most cases, individuals of the same species have the same number and types of chromosomes.
True
[Fun Facts]
Usual chromosome composition of human cells is two sets of 23 chromosomes, for a total of 46. Other diploid species have different numbers of chromosomes. The dog has 78 chromosomes (39 per set), the fruit fly has 8 chromosomes (4 per set), and the tomato has 24 chromosomes (12 per set).
None
What are the three most commonly used features to identify chromosomes in their metaphase form?
Size, location of centromere, and banding patterns (which are revealed when they are treated with stains).
What are the classifications for chromosomes based on centromere location?
Metacentric (near middle)
Submetacentric (off center)
Acrocentric (near one end)
Telocentric (at the end)
Chromosomal centromeres are never at the center, so how are the arms denoted?
Short arm is denoted p for petite and long arm is designated q.
Short arm can be nonexistent in telocentric chromatids.
How are the lengths of arms of the chromatids orientated when a karyotype is created?
Short arms are aligned towards the top.
How are the structures of chromosomes modified?
Through mutation
How are chromosomal mutations categorized as?
Deletions, duplications, inversion, and translocations
Which types of changes in chromosome structure do not affect the total amount of genetic material?
Inversions and reciprocal translocations do not affect the total amount of genetic material.
What are the possible effects of deletions and additions in chromosomes?
The possible effects depend on the size of the segment affected and whether it includes genes or portions of genes that are vital to the development of the organism. When a deletion or duplication has an effect, it is usually detrimental. Larger changes in the amount of genetic material tend to be more harmful because more genes are missing or duplicated.
What type of mutation involves a change in the direction of the genetic material along a single chromosome?
Inversion
What type of mutation in which one segment of a chromosome becomes attached to a different chromosome?
Translocation; consists of simple translocation and reciprocal translocation
What type of mutation in which a single piece of chromosome is attached to another chromosome?
Simple translocation
What type of mutation in which two different types of chromosomes exchange pieces, thereby producing two abnormal chromosomes carrying translocations?
Reciprocal translocation
What are the two variations in chromosome numbers?
Variation in the number of sets of chromosomes
Variation in the number of particular chromosomes within a set
What refers to an organism that has a chromosome number that is a multiple of a chromosome set (1n, 2n, 3n, etc.)?
Euploid (eu meaning true)
For example, in a species that is diploid, a euploid organism would have two sets of chromosomes in its somatic cells. In Drosophila melanogaster, for example, a normal individual has eight chromosomes.
What refers to an organism or cell that has three or more sets of chromosomes?
Polypoid
How is a diploid, triploid, and tetraploid denoted and all are considered euploid since they have complete sets of chromosomes?
2n, 3n, and 4n. The n represents the number of chromosomes in the complete set. For example, n = 23 in humans.
What is the second way a chromosome can vary which refers to an alternation in the number of a particular chromosome, so that the total number of chromosomes is not an exact multiple of a set?
Aneuploidy
For example, an abnormal fruit fly could have nine chromosomes instead of eight because it had three copies of chromosome 2 instead of the normal two copies.
Instead of being perfectly diploid, a trisomic animal is 2n + 1. Such an animal is said to have trisomy 2. By comparison, a fruit fly could be lacking a single chromosome, such as chromosome 3, and have a total of seven chromosomes (2n – 1). This animal is said to be monosomic and is described as having monosomy 3.
What is an event in which the chromosomes do not separate properly during cell division?
Nondisjunction
Nondisjunction can occur during meiosis I or meiosis II and produces haploid cells that have too many or too few chromosomes.
T/F In many cases, animals do not tolerate deviations from diploidy well. For example, polyploidy in mammals is generally a lethal condition.
True
However, a few cases of naturally occurring variations from diploidy do occur in animals. Male bees, which are produced from unfertilized eggs, contain a single set of chromosomes and are therefore haploid organisms. By comparison, fertilized eggs become female bees, which are diploid. A few examples of vertebrate polyploid animals have been discovered. Interestingly, on rare occasions, animals that are morphologically very similar to each other can be found as a diploid species as well as a separate polyploid species. This situation occurs among certain amphibians and reptiles.
What is the % of fertilized human eggs result in an embryo with an abnormality in chromosome number?
5 to 10%.
Approximately 50% of all spontaneous abortions are due to alterations in chromosome number.
[Focus Chromosome Abnormalities]
In some cases, an abnormality in chromosome number produces an offspring that can survive. Several human disorders are the result of abnormalities in chromosome number. The most common are trisomies of chromosomes 21, 18, or 13 and abnormalities in the number of the sex chromosomes
These syndromes are most likely due to nondisjunction. For example, Turner syndrome (XO) may occur when a gamete that is lacking a sex chromosome due to nondisjunction has fused with a gamete carrying an X chromosome. By comparison, triple X syndrome (XXX) occurs when a gamete carrying two X chromosomes fuses with a gamete carrying a single X chromosome.
Most of the known trisomies involve chromosomes that are relatively small, so they carry fewer genes. Trisomies of the other human chromosomes and most monosomies are presumed to be lethal and have been found in spontaneously aborted embryos and fetuses.
Human abnormalities in chromosome number are influenced by the age of the parents. Older parents are more likely to produce children with abnormalities in chromosome number, possibly because meiotic nondisjunction is more likely to occur in older cells. Down syndrome, which was first described by the English physician John Langdon Down in 1866, provides an example. This disorder is caused by the inheritance of three copies of chromosome 21. The incidence of Down syndrome rises with the age of either parent. In males, however, the rise occurs relatively late in life, usually past the age when most men have children. By comparison, the likelihood of having a child with Down syndrome rises dramatically during the later reproductive ages of women.
None
Cell division refers to the _______ of cells.
reproduction, multiplication, splitting, or duplication
The field of genetics that involves the microscopic examination of chromosomes is called ________
cytogenetics
What happens to chromosomes when a cell is about to divide?
Multiple choice question.
The chromosomes become flexible.
The chromosomes become lengthened.
The chromosomes become chromatin.
The chromosomes become compacted.
The chromosomes become compacted.
The two copies of a replicated chromosome are called sister __________
Chromatids
In humans, the X and Y chromosomes are called the ________ chromosomes.
Sex
The reproduction of cells is also known as cell _________.
Division
Autosomes are chromosomes that are not _________ chromosomes.
Sex
What field of study involves the microscopic examination of chromosomes and cell division?
Multiple choice question.
Phylogenetics
Cytogenetics
Ontogenetics
Mycology
Cytogenetics
What statement is true of eukaryotic chromosomes?
Multiple choice question.
There is one set of chromosomes in diploid cells.
They occur in pairs in haploid cells.
There are two sets of chromosomes in haploid cells.
They occur in pairs in diploid cells.
They occur in pairs in diploid cells.
When a cell prepares to divide, the chromosomes become more tightly compacted. This process decreases the apparent length of the chromosomes and increases their ________
diameter, width, visibility, or thickness
How many sets of chromosomes do the cells of many eukaryotic species have?
Multiple choice question.
Four
Six
Three
Two
Two
Chromosomes that have replicated consist of two copies that are still joined to each other. The two copies are referred to as a pair of ______.
Multiple choice question.
sister centromeres
sister homologs
sister chromatids
nonsister chromatids
nonsister homologs
sister chromatids
When the cells of an organism carry two sets of chromosomes, that organism is said to be ______
diploid or 2n
In humans, what chromosomes determine the sex of the individual?
Multiple choice question.
Chromosomes 21 and 22
X and Y chromosomes
Chromosomes 1 and 2
Autosomes
X and Y chromosomes
Sperm and egg cells are known as ________
gametes or sex cells
Chromosomes that are not sex chromosomes are called _____________
autosomes
Gametes are haploid. Haploid means that the cells contain how many sets of chromosomes?
Multiple choice question.
Three
Two
One
One
In ______ cells, eukaryotic chromosomes occur in ______.
Multiple choice question.
haploid; homologous pairs
haploid; double copies
diploid; single copies
diploid; homologous pairs
diploid; homologous pairs
If an organism is diploid, the two members of a pair of chromosomes are called _________.
homologs, homologues, homologous, homologous chromosomes, or homolog
In diploid eukaryotic organisms, most cells contain ___ sets of chromosomes.
2
How do the human sex chromosomes differ?
Multiple choice question.
In size but not in genetic composition
In genetic composition but not in size
In size and in genetic composition
They have the same size and genetic composition
In size and in genetic composition
A diploid organism contains ______.
Multiple choice question.
three sets of chromosomes
four sets of chromosomes
two chromosomes
four chromosomes
two sets of chromosomes
two sets of chromosomes
The sequence of growth, replication, and division that produces new cells is called ______.
Multiple choice question.
apoptosis
karyotyping
the kinetochore
the cell cycle
the cell cycle
The gametes are the ______ and _______ cells.
Blank 1: sperm or spermatocyte
Blank 2: egg or oocyte
Cells, such as gametes, that contain one set of chromosomes are called ______ cells.
Multiple choice question.
diploid
haploid
triploid
polyploid
haploid
In actively dividing cells, the G1, S, and G2 phases are collectively known as which of the following?
Multiple choice question.
Anaphase
Interphase
Metaphase
Prophase
Interphase
In a diploid organism, a pair of chromosomes consists of two ______.
Multiple choice question.
chromatids
genomes
alleles
homologs
homologs
In humans, two chromosomes are not considered homologous chromosomes, although they do have short regions of homology. These are the
____________ and ___________
chromosomes.
X and Y
In multicellular eukaryotic organisms, the production of new cells follows a highly regulated sequence of growth, DNA replication, and division. This sequence is referred to as the cell ____________
, which consists of the G1, S, G2, and M phases.
cycle
While preparing to divide, the cell grows and copies its chromosomes during ______.
Multiple choice question.
telophase
anaphase
metaphase
interphase
interphase
Identify the stage in the cell cycle that is considered the non-dividing stage.
Multiple choice question.
G0
G2
S
G1
G0
In actively dividing cells, the G1, S, and G2 phases are collectively known as ____________.
interphase
The phase of the eukaryotic cell cycle where chromosome replication occurs is the ________ phase.
S, synthesis, or interphase
During interphase of the cell cycle, the cell grows and copies which of the following in preparation for cell division?
Multiple choice question.
Ribosomes
Chromosomes
Chromatids
Chromosomes
In the G2 phase, the cell synthesizes ________ needed for chromosome sorting and cell division.
proteins or polypeptides
In a phase of the cell cycle the cell has postponed proceeding through G1 and is considered non-dividing. It is called the ________ phase.
G0
In most cases, mitosis is followed by the division of the cytoplasm to produce two distinct daughter cells. This process is known as _________
Cytokinesis
Both external and internal factors determine if a cell will __________.
divide, split, cleave, multiply, replicate, or duplicate
The progression through the cell cycle is highly regulated to ensure that the ______ is intact and the conditions are appropriate for a cell to divide.
Multiple choice question.
mitotic spindle
cleavage furrow
cell wall
nuclear genome
nuclear genome
Cells produce proteins that are necessary for chromosome sorting and cell division during what phase of the cell cycle?
Multiple choice question.
G1 phase
S phase
M phase
G2 phase
G2 phase
Mitosis is usually followed by cytokinesis, which is ______.
Multiple choice question.
the division of the cytoplasm to produce two daughter cells
duplication of the cytoplasm to produce two daughter cells
the reappearance of the nuclear membrane
the disappearance of the nuclear membrane
the division of the cytoplasm to produce two daughter cells
To assess if a cell is in an appropriate condition to divide, the cell employs sensors called ______ proteins.
Multiple choice question.
chaperone
kinetochore
spindle
checkpoint
checkpoint
In order to determine if a cell is in the proper conditions to divide, a cell employs ______ critical regulatory points called checkpoints.
Multiple choice question.
three
two
five
four
three
Select all that apply
Which of the following are internal factors that affect cell division?
Multiple select question.
Checkpoints
Cell cycle control molecules
Environmental conditions
Signaling molecules
Checkpoints
Cell cycle control molecules
During the process of ________ cell division, a cell divides to produce two new cells that are genetically identical to the original cell.
mitotic, mitosis, or binary fission
Name the region where the two sister chromatids are tightly associated.
Multiple choice question.
Telomere
Equatorial plate
Centromere
Centriole
Centromere
Checkpoint proteins act as ______ to determine if a cell is in the proper condition to divide.
Multiple choice question.
kinetochores
sensors
DNA repair enzymes
chromosome organizing centers
sensors
Which protein is necessary to hold the sister chromatids together at the centromere?
Multiple choice question.
Adhesin
Kinesin
Condesin
Cohesin
Cohesin
The three critical regulatory points found in the cell cycle of eukaryotic cells are called _________
checkpoints
What is the function of the mitotic spindle?
Multiple choice question.
Determines which chromosomes are organized into pairs
Compacts chromosomes into chromatids
Replicates chromosomes immediately before cell division
Organizes and sorts chromosomes during division
Organizes and sorts chromosomes during division
Question Mode
Multiple Choice Question
Mitotic cell division is a process by which a cell divides to produce ______ new daughter cells that are genetically ______ the original cell.
Multiple choice question.
two ; identical to
four ; different from
four ; identical to
two ; different from
two ; identical to
In a replicated chromosome, the two sister chromatids are bound closely at a region known as the __________.
centromere or centromeres
Mitosis is the cell division process that divides ______.
one cell nucleus into four nuclei
one cell nucleus into two nuclei
the cytoplasm
growth factors required for completion of G1
one cell nucleus into two nuclei
Select all that apply
Prophase of mitosis is characterized by which of the following?
Multiple select question.
Nucleolus is visible.
Nuclear envelope begins to dissociate.
Nuclear envelope forms.
Sister chromatids separate from each other.
Nucleolus is no longer visible.
Sister chromatids are visible by light microscopy.
Nuclear envelope begins to dissociate.
Nucleolus is no longer visible.
Sister chromatids are visible by light microscopy.
What cell structure is composed of microtubules and is responsible for organizing and sorting the chromosomes during cell division?
Multiple choice question.
Mitotic handle
Metaphase plate
Kinetochore
Mitotic spindle
Mitotic spindle
Select all that apply
Which of the following events occur during prometaphase of mitosis?
Multiple select question.
The mitotic spindle is fully formed.
The centrosomes move apart and demarcate the two poles.
The spindle fibers interact with the sister chromatids.
The homologous chromosome pairs align with each other.
The sister chromatids of a chromosome are separated.
The nuclear envelope completely fragments into small vesicles.
The mitotic spindle is fully formed.
The centrosomes move apart and demarcate the two poles.
The spindle fibers interact with the sister chromatids.
The nuclear envelope completely fragments into small vesicles.
The metaphase plate is a plane located ______.
Multiple choice question.
halfway between the poles
just under the plasma membrane
near one of the poles
between a centriole pair in a centrosome
halfway between the poles
Mitotic cell division in humans is ______.
Multiple choice question.
cell division that results in two diploid daughter cells
cell division that results in production of gametes
cell growth that results in very large cells
cell division that results in two haploid daughter cells
cell division that results in two diploid daughter cells
At anaphase of mitosis, sister __________ separate from one another and begin to move toward the poles of the cell.
chromatids
During ______ of mitosis, the kinetochore microtubules shorten, pulling the chromosomes toward the pole to which they are attached.
Multiple choice question.
anaphase
prophase
prometaphase
metaphase
anaphase
Which of these is one of the significant results of meiosis?
Multiple choice question.
It creates zygotes that grow to become new individuals.
It creates diploid gametes for sexual reproduction.
It creates diploid cells that grow to become new individuals.
It creates haploid gametes for sexual reproduction.
It creates haploid gametes for sexual reproduction.
Bivalent formation and crossing over are two key events that typically occur at the beginning of which of these?
Multiple choice question.
Mitosis only
Meiosis only
Both mitosis and meiosis
Neither mitosis nor meiosis
Meiosis only
The process of forming a bivalent is termed pairing, or _____________
Syapsis
During telophase, the nuclear envelope re-forms to produce two separate
nuclei or nucleus
Crossing over is best described as which of these?
Multiple choice question.
It may or may not involve a physical exchange of chromosome segments in the tetrad depending on whether the cell is prokaryotic or eukaryotic.
It involves a physical exchange of chromosome segments in the tetrad.
It does not involve a physical exchange of chromosome segments in the tetrad.
It involves a physical exchange of chromosome segments in the tetrad.
Which of these is the process by which homologues exchange chromosome segments at the beginning of meiosis to increase genetic variability in offspring?
Multiple choice question.
Crossing over
Cytokinesis
DNA replication
Synapsis
Crossing over
Which two key events occur at the beginning of meiosis but not mitosis?
Multiple select question.
Crossing over
Formation of bivalents
Breakdown of nuclear envelope
Duplication of chromosomes
Crossing over
Formation of bivalents
Meiosis I sorting separates which of these?
Multiple choice question.
Homologous chromosomes
Nuclear envelopes
Sister chromatids of a chromosome
Homologous chromosomes
Synapsis is the process of forming a(n) __________
bivalent or tetrad
The sister chromatids are separated during _________ II of meiosis.
anaphase
What statement about mitosis and meiosis is correct?
Multiple choice question.
Sister chromatids are separated both during mitosis and meiosis.
Mitosis and meiosis both form haploid daughter cells.
Crossing over only occurs in mitosis.
Homologous pairs are separated both in mitosis and meiosis.
Sister chromatids are separated both during mitosis and meiosis.
Homologous chromosomes are separated from each other during ______.
Multiple choice question.
meiosis I only
meiosis II only
meiosis I and II
mitosis only
meiosis I only
When two haploid gametes unite, they create a diploid cell called a(n) _______.
zygote or diploid zygote
The study of chromosomal variation is important because these variations in chromosome structure and number can have major effects on the characteristics of an organism. Also, these changes have been an important force in the __________ of new species.
evolution or origin
In a particular species, the composition of chromosomes remains relatively ______.
Multiple choice question.
constant
variable
unstable
constant
In what phase of meiosis are sister chromatids separated?
Multiple choice question.
Anaphase II
Anaphase I
Telophase II
Metaphase I
Metaphase II
Anaphase II
Select all that apply
Which of the following statements correctly compare mitosis and meiosis?
Multiple select question.
Crossing over occurs in meiosis but not normally in mitosis.
Mitosis and meiosis form haploid daughter cells.
Sister chromatids are separated during both mitosis and meiosis.
Meiosis has fewer steps than mitosis.
Homologous pairs are separated into different cells in both mitosis and meiosis.
Crossing over occurs in meiosis but not normally in mitosis.
Sister chromatids are separated during both mitosis and meiosis.
What chromosomal variations have major effects on the characteristics of an organism?
Multiple select question.
Composition
Structure
Appearance
Number
Structure
Number
An alteration in the number of particular chromosomes so that the total number of chromosomes is not an exact multiple of a set is referred to as __________.
aneuploidy or aneuploid
What statement about mitosis and meiosis is correct?
Multiple choice question.
Mitosis and meiosis both form haploid daughter cells.
Sister chromatids are separated both during mitosis and meiosis.
Crossing over only occurs in mitosis.
Homologous pairs are separated both in mitosis and meiosis.
Sister chromatids are separated both during mitosis and meiosis.
Polyploidy is generally a lethal condition in ______.
Multiple choice question.
reptiles
mammals
amphibians
plants
mammals
Quiz Start
Down’s syndrome is an example of aneuploidy which is when
Question 1 options:
Individuals have an abnormality in chromosome number
Individual are unable to complete spermatogenesis (male) or oogenesis (female)
There are errors in anaphase of mitosis
Sister chromatids fail to form during the S phase
Individuals have an abnormality in chromosome number
At the end of the first meiotic division (Meiosis 1), each chromosome consists of
Question 2 options:
A chiasmata
A homologous chromosome pair
Four copies of each DNA molecule
Two sister chromatids
A homologous chromosome pair WRONG
If crossing over occurs between two chromatids on a single pair of homologous chromosomes, how many will have a recombinant chromosome?
Question 4 options:
all 4
1 of the 4
2 of the 4
3 of the 4
none of them
all 4 WRONG
What is the biggest difference between anaphase of mitosis and anaphase 1 of meiosis?
Question 5 options:
In anaphase of mitosis the sister chromatids separate and in anaphase 1 of meiosis the homologous pairs separate
In anaphase of mitosis the homologous pairs separate and in anaphase 1 of meiosis the sister chromatids separate
In anaphase of mitosis the DNA is replicated and in anaphase 1 of meiosis the RNA is replicated
In anaphase of mitosis the sister chromatids line up along the middle and in anaphase 1 of meiosis the sister chromatids separate
In anaphase of mitosis the sister chromatids separate and in anaphase 1 of meiosis the homologous pairs separate
When a single chromosome has completed replication it now
Question 7 options:
Consists of sister chromatids
Consists of two homologous pairs
Is single stranded
Is in the open conformation
Consists of sister chromatids
If a homologous pair of chromosomes fails to separate during Meiosis I, what will be the result at the end of Meiosis II?
Question 8 options:
2 gametes will have 2 of these chromosomes and 2 will have 0 of these chromosomes
None of the gametes will have the affected chromosomes.
2 gametes will be normal, 1 gamete will have 2 of the affected chromosomes and 1 gamete will have 0 of the affected chromosomes.
2 gametes will be normal and 2 gametes will have 2 of the affected chromosomes.
2 gametes will have 2 of these chromosomes and 2 will have 0 of these chromosomes
A researcher is looking at a cell during G1. She comments that the chromosomes consist of sister chromatids. Why is she incorrect?
Question 9 options:
DNA replication only occurs during the S phase, which hasn’t happened yet for this cell
Sister chromatids are only found during cytokinesis
During the G1 phase, the sister chromatids are pulling apart
During the G1 phase, all of the chromosomes are in tetrads, not as sister chromatids
DNA replication only occurs during the S phase, which hasn’t happened yet for this cell
The American Bison has a total of 60 chromosomes. How many chromosomes would be found in its sperm?
Question 10 options:
23
30
46
60
30
The Tasmanian Devil has 14 chromosomes in 7 homologous pairs. After meiosis, the Devil has
Question 11 options:
Two cells with 7 chromosomes each in 3.5 homologous pairs
Two cells with 14 chromosomes each in 7 homologous pairs
Four cells with 7 chromosomes each in 0 homologous pairs
Four cells with 14 chromosomes each in 0 homologous pairs
Four cells with 7 chromosomes each in 0 homologous pairs
In which phase of the cell are chromosomes replicated?
Question 12 options:
G1
S
G2
Mitosis
S
I am looking at a cell and see two chromosomes with the same basic genes (for example genes for finger length and hairline shape). However, when I sequences these two chromosomes they are similar but not identical in their DNA sequence. This means
Question 13 options:
They are members of a homologous pair
They are sister chromatids
They are from fraternal twins
They are from identical twins
Both B and C
Both B and C WRONG
At the beginning of a cell event I see 30 chromosomes in 15 homologous pairs. At the end of the cell event I have four cells each of which has 15 chromosomes in no homologous pairs. What cellular event just occurred?
Question 14 options:
Mitosis
Meiosis
Transcription
Translation
Meiosis
The final goal of mitosis is
Question 15 options:
Four haploid cells
Four diploid cells with identical nuclei
Two diploid cells with identical nuclei
Two haploid cells
Two diploid cells with identical nuclei
