Cell Divison
At the end of meiosis II, each chromosome consists of how many chromatid(s)?
one The final products of meiosis are four haploid daughter cells, where each chromosome has only one chromatid.
Centrosomes are located near which organelle?
Nucleus
If 2n=8, how many chromatids are present during metaphase of mitosis?
16 Metaphase is the stage of mitosis where the spindle apparatus guides chromosomes to the cell equator (midpoint), which is called the metaphase plate. The dyads will be lined up in a single file at the end of metaphase. In the 2n=8 cell, there are 8 chromosomes present during metaphase, but 16 chromatids.
If 2n=8, how many chromatids are present at the end of anaphase I of meiosis?
16 When anaphase I begins, you may expect the chromosome number to change, but it does not. Remember, it is only after the sister chromatids separate that the chromosome number changes. Since anaphase I only separates the homologous chromosomes, neither the chromosome number nor the chromatid number changes during anaphase I. This is visually represented below:
If 2n=46, how many chromosomes are present at the end of metaphase II?
23 During metaphase II, the chromosomes are lined up individually across the center of the cell. Due to the reduction division of meiosis I, there are now half as many chromosomes and chromatids as there were before. For humans, this means that there will be 23 chromosomes and 46 chromatids at the start of anaphase II. Below is a table summarizing the chromosome and chromatid number during meiosis II in humans:
How many copies of paired chromosomes do human somatic cells contain?
23 Human somatic (body) cells contain 46 chromosomes, or 23 copies of paired chromosomes.
If 2n=24, how many chromosomes are present at the end of metaphase I of meiosis?
24 Recall that there are two divisions during meiosis: meiosis I and meiosis II. The genetic material of the cell is duplicated during S phase of interphase, just as it was with mitosis. In the 2n=24 cell, this results in 24 chromosomes and 48 chromatids during prophase I and metaphase I. However, these chromosomes are not arranged in the same way as they were during mitosis. Rather than each chromosome lining up individually across the center of the cell, homologous pairs of chromosomes line up together (forming tetrads, also known as bivalents):
If 2n=46, how many chromosomes are present at the end of anaphase II of meiosis?
46 When anaphase II begins, the sister chromatids split apart, which doubles the chromosome number. For humans, this means that there will be 46 chromosomes and 46 chromatids during anaphase II. These numbers remain the same during telophase II. Below is a table summarizing the chromosome and chromatid number during meiosis II in humans:
If 2n=24, how many chromosomes are present during anaphase of mitosis?
48 When sister chromatids separate (a step signaling that anaphase has begun), each chromatid is considered an individual chromosome. For this reason, the chromosome number doubles during anaphase. The 2n=24 cell progresses from having 24 chromosomes to 48 chromosomes during anaphase.
If 2n=8, how many chromosomes are present in each daughter cell after mitosis has ended?
8 It is only after the end of mitosis, when the dividing cells have fully separated and the membranes have reformed, that the normal chromosome number is restored to the cell. Considering the 2n=8 cell, each separated daughter cell will have 8 chromosomes after the end of mitosis.
How are microtubules arranged in centrioles?
9 x 3 array Centrioles are specialized cylinders of microtubules that inhabit the centrosome. Each centriole is a hollow cylinder made of nine triplets of microtubules (a 9x3 array).
Interphase accounts for how much of the cell cycle?
90% The cell cycle is the lifecycle of a cell. It is where cells do their usual tasks, grow, and divide. The cell cycle consists of two broad phases: 1. Interphase accounts for at least 90% of the cell cycle, as is depicted by the orange region of the picture below. 2. M phase is depicted by the yellow region in the picture below.
A cell fails to contact and attach itself to a stable surface, and therefore is unable to grow. Which cell specific regulation does this scenario describe? A. Anchorage dependence B. M checkpoint C. Cyclin dependent kinases D. Growth factors E. End of G1 checkpoint
A! Anchorage dependence is the need for contact and anchorage to a stable surface by some cells in order for them to grow, function, and divide, especially when grown in cell cultures. In fact, most cells only divide when attached to an external surface such as neighboring cells or the side of a culture dish.
Which of the following does NOT occur during the G2 phase? A. Condensing chromatin into chromosomes. B. Evaluating the accuracy of DNA replication. C. Replication of organelles. D. Checking for sufficient mitosis promoting factor levels.
A! Gap phase 2 (G2): Here, the cell continues to grow and prepare for division by checking the accuracy of DNA replication. It also checks for mitosis promoting factor (MPF), a regulatory protein/enzyme that needs to be present in adequate amounts for mitosis to occur. Cells will also replicate their organelles during this phase. Chromatin is not condensed into chromosomes until the start of mitosis (M phase).
Which type of microtubule does NOT help move the MTOCs to opposite poles of the cell? A. Kinetochore microtubules B. Astral microtubules C. Polar microtubules
A! Within the spindle apparatus, both astral and polar microtubules function to orient the MTOCs. Astral microtubules extend from the centrosomes to the cell membrane. They are involved with spindle apparatus orientation, because they pull the MTOCs toward the opposite poles of the cell. Polar microtubules emanate from each MTOC and connect with each other. As they continue to grow after connecting, they help push the MTOC to opposite ends of the cell.
Sister chromatids split during which stage of meiosis?
Anaphase II Meiosis can be divided into two main components: meiosis I and meiosis II. During meiosis I, homologous chromosomes are split. During meiosis II, sister chromatids are split. Anaphase II pulls the sister chromatids of each chromosome apart at the centromere. This doubles the number of centromeres (and therefore chromosomes) in each cell. As the kinetochore microtubules shorten, the separated chromatids (now chromosomes) will be pulled to opposite poles.
During what phase of mitosis does cytokinesis begin in animal cells and plant cells, respectively?
Anaphase; telophase Cytokinesis tends to begin in late anaphase of animal cells. In contrast, cytokinesis tends to start around telophase in plant cells.
Which of the following conditions would promote cell division?
Anchorage to neighboring cells
Which of the following cells contain centrosomes?
Animal cells A centrosome is an organelle found within animal cells that is a type of MTOC. Note: Fungi and most plant cells do not contain a centrosome as their MTOC. Rather, in fungi and most plant cells, we typically just refer to the MTOCs as 'MTOCs'.
Which of the following is NOT true of cytokinesis? A. Physically separates cell membrane. B. Occurs before karyokinesis. C. Results in divided cytoplasm. D. Last stage of cell division.
B! Cytokinesis is the physical process of cell division. This is the process that occurs after karyokinesis, and it physically separates the cytoplasm and cell membrane.
Which of the following describes a cell that is NOT in the G0 phase? A. Beating cardiomyocyte B. Dividing epithelial cell C. Contracting myocyte D. Firing neuron
B! G0 phase: This is a sort of 'hangout' spot, where cells that aren't ready to divide just 'do their thing'. For example, heart cells will beat, muscle cells will contract, neurons will send action potentials, red blood cells will carry oxygen, etc. Cells that will not divide after their creation (like heart cells and neurons) are permanently in G0.
Suppose a cell fails the M checkpoint, so that its chromosomes are unable to attach to spindle fibers. Which process will be directly affected? A. Chromatin will be unable to condense into chromosomes. B. Sister chromatids will be unable to separate from each other. C. Nuclear membranes cannot reform around the chromosomes at each pole. D. Vesicles from the Golgi apparatus cannot fuse to create the cell plate.
B! If chromosomes aren't attached to spindle fibers, the M checkpoint fails and the cell cannot proceed with anaphase, which is the phase when sister chromatids are pulled apart.
How do mitochondria and chloroplasts reproduce?
Binary fission is how archaea, bacteria, and certain organelles (mitochondria and chloroplasts) reproduce.
Which of the following statements about the G2 checkpoint is NOT true? A. The cell evaluates the accuracy of DNA replication. B. If conditions are favorable, the cell proceeds to prophase. C. Mitosis stops if chromosomes are not attached to spindle fibers. D. The cell checks for sufficient mitosis promoting factor levels.
C!
Which of the following does NOT accurately describe the G1 phase? A. The cell produces more cytoplasm, proteins, and organelles. B. The cell physically grows in preparation for a future division. C. If conditions are favorable, the cell proceeds to the G2 phase. D. If conditions are not favorable, the cell proceeds to the G0 phase.
C! Gap phase 1 (G1): This is where the cell physically grows in preparation of a future division. Here, a cell will produce more cytoplasm, proteins, and organelles. The cell will also assess the conditions it finds itself in. If conditions are not favorable for a division, it will enter the G0 phase. If conditions are favorable, and it is a cell which actively divides, it will proceed to the S phase.
Which of the following occurs during metaphase of mitosis? A. Nuclear membranes reform B. Chromosome number doubles C. Dyads line up at the cell equator D. Chromatin condenses into chromosomes
C! Metaphase is the stage of mitosis where the spindle apparatus guides chromosomes to the cell equator (midpoint), which is called the metaphase plate. The dyads will be lined up in a single file at the end of metaphase
Cytokinesis occurs in plant cells via the formation of which structure?
Cell plate In cytokinesis of plant cells, the Golgi apparatus releases vesicles, which fuse in the center of the cell and grow outward into the membrane, creating a cell plate. The cell plate these vesicles form eventually transforms into the middle lamella, which cements adjacent plant cells together.
What connects sister chromatids to form a dyad?
Centromere Centromeres are regions of DNA that link sister chromatids together, in order to form a dyad. Dyads are replicated chromosomes that look like an X, where each half of the X is a sister chromatid that represents half of the replicated chromosome.
Which term describes the region of DNA that links sister chromatids together to form a dyad?
Centromere Don't confuse centromere with centrosome! Centromeres are regions of DNA that link sister chromatids together in order to form a dyad. They also assemble kinetochores. A centrosome is an organelle found within animal cells, that is a type of MTOC.
Where do chromosomes break apart during anaphase of mitosis, and how does that change the chromosome number?
Centromere; doubles During anaphase, kinetochore microtubules shorten to pull centromeres apart. When the centromere splits into two, the X shaped dyad also splits into two. Each of these chromatids will have their own piece of the centromere. When the sister chromatids have separated, they are now each considered their own chromosome. For this reason, the chromosome number doubles during anaphase.
Which structure directly allows genetic recombination to occur during prophase I of meiosis?
Chiasmata Chiasmata are regions where homologous chromosome pairs physically crossover in a bivalent/tetrad. These are what allow for genetic recombination to occur. Genetic recombination occurs when a crossover event produces chromosomes that haven't been seen in either parent, making genetically diverse offspring.
Which form of DNA is more densely packed?
Chromatin Chromatin is the general packaging of DNA around histone proteins - this arrangement of DNA helps to condense DNA to fit within the nucleus of the cell. Throughout most of the cell cycle, DNA is packaged in the form of chromatin. However, during mitosis and meiosis, chromatin exists in an additional level of organization known as a chromosome. Chromosomes are an even denser packaging of chromatin that are visible with a light microscope, particularly during metaphase.
Which process is NOT a form of cell division? A. Mitosis B. Meiosis C. Conjugation D. Binary fission
Conjugation! There are three main types of cell division you could run into on the DAT: Mitosis Meiosis Binary fission
Which stage is NOT a part of interphase?
Cytokinesis Interphase can be broken down into the following stages: G0, G1, S, and G2. While the M phase consists of mitosis (aka karyokinesis) and cytokinesis. Mnemonic for the cell cycle: - Go = Gap Phase 1 (G₁) of interphase - Sam = Synthesis Phase of interphase - Go = Gap Phase 2 (G₂) of interphase - Make = Mitosis of the M phase - Cake = Cytokinesis of the M phase
Which of the following does NOT accurately describe gametocytes? A. Diploid germ cells B. Divide by meiosis to form gametes C. Divide by mitosis to form more gametocytes D. Contain half the number of chromosomes as somatic cells
D! Gametocytes are diploid germ cells that help to create gametes. They can divide by mitosis to form more gametocytes (replenishing the parental germ line); or, they divide by meiosis to form gametes. Human somatic cells are diploid with 46 chromosomes. Both gametocytes and somatic cells contain two complete sets of chromosomes.
Which of the following does NOT occur during telophase of mitosis? A. Nucleoli reappear B. Nuclear membranes reform C. Chromosomes decondense D. Spindle apparatus appears
D! Telophase occurs after chromosomes have been segregated to either end of the cell. Here, nuclear membranes reform around the chromosomes at each pole. Similarly, the nucleoli will reappear inside of the nucleus. Finally, the chromosomes decondense back into chromatin and the spindle apparatus breaks down.
Which of the following is NOT a cell specific regulation that limits cell division? A. M checkpoint B. Cyclin dependent kinases C. Density dependent inhibition D. End of G0 checkpoint E. Anchorage dependence
D! The cell cycle influences cell division through functional limitations to cell growth, as well as cell specific regulations. These various mechanisms are in place to ensure that a cell does not grow and divide uncontrollably, becoming cancerous. Cell specific regulations include the following: cell cycle checkpoints, cyclin dependent kinases (CDKs), growth factors, density dependent inhibition, and anchorage dependence.
Which of the following is NOT a statement from the cell theory? A. All living creatures are made of cells. B. All cells originate from preexisting cells. C. Cells are the basic structural unit of all organisms. D. Cells can arise spontaneously from matter.
D! The cell theory states that all living creatures are made of cells, which are the basic structural units of all organisms. This theory also states that cells originate from preexisting cells through the process of cell division. Therefore, cells are not able to arise spontaneously from non-living matter.
Which of the following statements about centrioles is NOT true? A. The pericentriolar material of a centrosome surrounds the centrioles. B. Centrioles determine where other organelles are placed. C. The basal body produces a cilium or flagellum for the cell. D. The pericentriolar material secures microtubules to kinetochores.
D! The pericentriolar material of a centrosome is a matrix of proteins that surround the centrioles. These proteins play a role in microtubule nucleation, which is the process where several individual microtubules come together. Similarly, the pericentriolar material is involved with securing microtubules to the centrosome. When the mother centriole attaches to the cell membrane, a basal body is formed, which can produce a cilium or a flagellum for the cell. Centrioles determine where the nucleus and other organelles are placed within the cell. Remember, centrioles are the active components of a centrosome, which is an animal cell's MTOC.
Which of the following microtubules are NOT a component of the spindle apparatus? A. Astral microtubules B. Kinetochore microtubules C. Polar microtubules D. Equatorial microtubules
D! There are three main types of microtubules in the spindle apparatus: 1. Kinetochore microtubules (K-fibers) 2. Astral microtubules 3. Polar microtubules
Which term describes the identical copies of a replicated chromosome?
During cell division, each chromosome gets replicated. Sister chromatids are identical copies of a replicated chromosome. While the sister chromatids are attached to each other, they are considered one chromosome. As soon as the sister chromatids are pulled apart and separated during cell division, they are now each considered to be separate chromosomes.
Which term describes somatic cells containing two complete sets of chromosomes?
Diploid Ploidy refers to the number of chromosome sets found in a cell. Diploid organisms (like humans) have somatic cells containing two complete sets of chromosomes.
Fertilization of two human gametes will result in which of the following?
Diploid zygote with 46 chromosomes Gametes are haploid cells containing just 23 chromosomes. These are used by organisms during sexual reproduction. Fertilization of two gametes that have 23 chromosomes (from the same species, but opposite sexes) will conceive a zygote that is diploid with 46 chromosomes.
How does the the number of chromatids compare to the number of chromosomes at the beginning of mitosis?
Double Chromosomes can exist in duplicated or unduplicated states. At the beginning of mitosis, for example, a chromosome consists of two sister chromatids - chromatids are the term used to describe the chromosome in its duplicated state. Therefore, there are double the number of chromatids than chromosomes at the beginning of mitosis.
Which of the following occurs at the end of meiosis I in preparation for meiosis II?
Dyad chromosomes decondense back into chromatin Telophase and cytokinesis I occur after the bivalent/tetrad homologs have been pulled to opposite cell poles. Once the two new nuclear envelopes have formed, we will have two daughter nuclei containing a haploid number of chromosomes. This is why we call meiosis a reductional division! The haploid number of dyad chromosomes will decondense back into chromatin in preparation for meiosis II. Cytokinesis I will occur by the formation of a cleavage furrow (animal) or cell plate (plant). Sometimes, cytokinesis will not even occur after meiosis I.
During synapsis, what two things are paired up via the synaptonemal complex?
Dyads Synapsis describes the process of homologous dyads pairing up to form bivalents or tetrads, via the synaptonemal complex. The synaptonemal complex is a protein structure that temporarily forms between homologous dyads. Bivalents (or tetrads) are a pair of two homologous dyads, each containing a pair of sister chromatids.
Failure at which checkpoint will cause the cell to enter the G0 phase?
End of G1 checkpoint If the end of G1 checkpoint fails, the cell enters the G0 phase.
Microtubule organizing centers are found in which cells?
Eukaryotic Microtubule organizing centers (MTOCs) are found in eukaryotic cells. Prokaryotes divide by binary fission and do not possess MTOCs. MTOCs create, extend, and organize the cell's microtubules.
How many daughter cells are produced in meiosis, and what is their ploidy?
Four haploid Meiosis involves the same general stages as mitotic karyokinesis (prophase, metaphase, anaphase, and telophase). However, the main difference is that these stages occur twice, which produces a total of four haploid daughter cells (haploid germ cells) from one diploid parent cell.
After the genome is replicated, which phase does the cell proceed to?
G2 phase Synthesis phase (S): This is where a cell will replicate its genome in preparation of an ensuing cell division. After the genome has been replicated, the cell will progress to the G2 phase of interphase.
Which term describes all of the DNA within a cell?
Genome The genome is all of the DNA within a cell. The entire genome is distributed amongst multiple chromosomes.
What cells divide to form gametes, and by which process does this occur?
Germ; meiosis Germ cells divide by meiosis to form gametes. Germ cells are diploid with 46 chromosomes. Gametes are haploid cells containing just 23 chromosomes.
During cytokinesis in plant cells, which organelle releases the vesicles that eventually form the middle lamella?
Golgi apparatus During cytokinesis in plant cells, the Golgi apparatus releases vesicles, which fuse in the center of the cell and grow outward into the membrane, creating a cell plate. The cell plate these vesicles form eventually transforms into the middle lamella, which cements adjacent plant cells together.
Which of the following accurately describes human gametes?
Haploid, one chromosomal set Haploid cells have half the number of chromosomal sets as a somatic cell, meaning they contain just one chromosomal set. In this way, haploid is a term that uniquely describes gamete cells. Human gametes have a haploid number of 23 chromosomes.
What type of cell does meiosis II begin with, and what gets separated within those cells?
Haploid; sister chromatids Meiosis II is the second meiotic division, and it looks a lot like mitosis. This is because we separate sister chromatids in meiosis II, just like we did in mitosis. The main difference is that we will be separating sister chromatids of two haploid cells in order to produce four haploid daughter cells.
What is the correct order of the following steps? I. Spindle apparatus breaks down II. Spindle apparatus guides chromosomes to the metaphase plate III. Nuclear envelope disappears IV. Sister chromatids move to opposite poles of the cell
III, II, IV, I The nuclear envelope disappears during prophase. During metaphase, the spindle apparatus guides chromosomes to the metaphase plate. Then, sister chromatids are pulled to opposite sides of the cell in anaphase. Finally, once the chromosomes have been segregated, the spindle apparatus is no longer needed and will break down in telophase.
Which of the following conditions would halt cell division?
Insufficient levels of mitosis promoting factor
What connects the mother centriole and daughter centriole in each centrosome?
Interconnecting fibers There is a mother centriole and a daughter centriole in each centrosome. This pair is oriented at a ninety degree angle with respect to each other, and they are connected by interconnecting fibers.
Which process divides one parent nucleus to form two daughter nuclei?
Karyokinesis
Which enzyme catalyzes the phosphorylation of specific substrates?
Kinase A kinase is an enzyme that phosphorylates substrates. Specifically, a kinase transfers a phosphate group from an ATP molecule.
When cyclin levels are low, what is the effect on cyclin dependent kinase?
Low activity Cyclin (the 'C' in 'CDK', or cyclin dependent kinase) is a protein that cycles up and down in amount through the stages of synthesis and degradation. As a result of this, it was named CYCLin. Cyclin activates CDKs. Therefore, when cyclin levels are high, CDK activity will be high and cell cycle progression will be rapid. Conversely, when cyclin is low, CDK activity will be low and cell cycle progression will be slowed down. Note: We do not need to memorize the names of the cyclins and CDKs in the image above. This is simply an illustration to show you that different cyclins, and cyclin dependent kinases play a regulatory role in the cell cycle and its progression.
During which phase of the cell cycle does karyokinesis occur?
M phase M phase is depicted by the yellow region in the picture below. It consists of karyokinesis (division of the replicated DNA and nucleus), which is subsequently followed by cytokinesis (division of the cell).
Where do kinetochore microtubules emanate from, and where do they connect to?
MTOC; chromosome Within the spindle apparatus, kinetochore microtubules (K fibers) are produced by the mitotic spindle, and they attach to a chromosome's kinetochore.
Which component of meiosis is defined as reductional division?
Meiosis I Meiosis I is known as reductional division because a diploid parent cell will divide into two haploid daughter cells (which will then go onto divide again during meiosis II). After meiosis I, the ploidy of each cell will be reduced by half. This is achieved because meiosis I separates homologous chromosomes.
During which phase of mitosis can karyotyping be performed?
Metaphase Karyotyping is a biological laboratory technique that allows scientists to visualize a cell's chromosomes. It is usually performed during metaphase.
Tetrads line up along the cell equator during which phase of meiosis?
Metaphase I Metaphase I is where bivalents/tetrads line up in double file along the metaphase plate, thanks to the meiotic spindle apparatus formed during diakinesis. This double file arrangement is completely random, which contributes to the genetic diversity of the daughter cells.
Which of the following most resembles metaphase II of meiosis?
Metaphase of mitosis Metaphase II looks just like metaphase in mitosis, because chromosomes (containing sister chromatids) line up in single file along the metaphase plate. However, remember we are talking about meiosis II, so each cell will have a haploid number of chromosomes.
The spindle apparatus is formed during which process(es)?
Mitosis and meiosis Mitotic and meiotic cells use a spindle apparatus to guide their chromosomes, but there is no spindle apparatus in binary fission.
How is a basal body formed?
Mother centriole attaches to cell membrane There is a mother centriole and a daughter centriole in each centrosome. In addition to being involved with cell division, the mother centriole can attach to the cell membrane and form a basal body, which can produce a cilium or a flagellum for the cell.
During cytokinesis in animal cells, what causes the contractile ring to get tighter and pinch the cell in two?
Myosin motors traveling along microfilaments During cytokinesis in animal cells, myosin motors travel along actin microfilaments and contract, pulling the plasma membrane toward the center of the cell. This creates a contractile ring that gets tighter, until it eventually pinches the cell in two.
Which term accurately describes the X and Y chromosomes?
Non-homologous The sex chromosomes (X and Y) are non-homologous because they do not contain the same genes. While autosomes may have different alleles, they still encode the same genes at the same loci, which is why they are considered homologous. The image below represents a male's DNA, arranged by chromosome number. Note that even visually, the sex chromosome pair (XY) is non-homologous.
What happens to the nucleolus and spindle apparatus during prophase of mitosis?
Nucleolus disappears; spindle apparatus forms
What happens to the spindle apparatus during anaphase of mitosis?
Polar microtubules lengthen; kinetochore microtubules shorten During anaphase, polar microtubules lengthen in order to stretch the cell. Conversely, kinetochore microtubules shorten to pull centromeres apart.
Which of the following statements does NOT accurately describe anaphase I of meiosis? A. Anaphase I separates homologous chromosomes from each other. B. Each bivalent must have at least one chiasmata for anaphase I to proceed. C. Polar microtubules shorten to separate homologous chromosomes. D. Anaphase I will not begin until each homolog is attached to a kinetochore microtubule.
Polar microtubules shorten to separate homologous chromosomes Anaphase I separates homologous chromosomes from each other by kinetochore microtubule shortening. Subsequently, each homolog is pulled from their double file arrangement at the metaphase plate to opposite poles of the dividing cell. Note: Anaphase I separates homologous chromosomes. Sister chromatids are not separated here. Anaphase I will not commence until the cell has determined that each bivalent/tetrad has at least one chiasmata. Moreover, each homolog in a bivalent/tetrad needs to be attached to a kinetochore microtubule in order for anaphase I to begin.
When certain substrates have been phosphorylated by a cyclin dependent kinase, what happens to the cell cycle?
Proceeds to next stage Cyclin dependent kinases (CDKs) are specifically regulated kinases. When certain substrates have been phosphorylated by a CDK, it serves as a signal for progression to the next cell cycle stage. The absence of this phosphorylation is a signal that the cell cycle should not progress.
Crossing over occurs during which phase of meiosis?
Prophase I Prophase I is where chromatin condenses into chromosomes, the nucleolus disappears, and the nuclear membrane disassembles. Pairing of homologous chromosomes and crossing over also occurs here, which creates genetic diversity and ensures that the homologous chromosomes are accurately segregated by meiosis I.
During which phase(s) of meiosis does chromatin condense into chromosomes?
Prophase I and prophase II Prophase I is where chromatin condenses into chromosomes, the nucleolus disappears, and the nuclear membrane disassembles. Pairing of homologous chromosomes and crossing over also occurs here, which creates genetic diversity and ensures that the homologous chromosomes are accurately segregated by meiosis I. Prophase II is where we (again) see the chromatin condensing into chromosomes, as well as nucleoli disappearing and the nuclear envelope disintegrating. While all of this is occurring, the centrosomes will migrate to opposite ends of the cells to form the meiotic spindle apparatus.
Which of the following phases of meiosis does NOT contribute to genetic diversity? A. Prophase I B. Metaphase I C. Prophase II D. Metaphase II
Prophase II Prophase I is where homologous chromosomes pair up and crossing over occurs via synapsis. This creates genetic diversity. Metaphase I is where bivalents/tetrad line up in double file along the metaphase plate. This double file arrangement is completely random, which contributes to the genetic diversity of the daughter cells. Prophase II occurs within haploid cells. Therefore, we will not see synapsis occur during this phase. This implies that we will not introduce any genetic variation in prophase II. Metaphase II is where dyads line up in single file along the metaphase plate. This single file arrangement is completely random, which contributes to the genetic diversity of the daughter cells.
Consider a liver cell that is currently in the G0 phase. When conditions become favorable, what phase will it proceed to?
S phase G0 phase: This is a sort of 'hangout' spot, where cells that aren't ready to divide just 'do their thing'. Cells that will not divide after their creation (like heart cells and neurons) are permanently in G0. Cells that will divide will progress to the S phase when they are ready.
During which phase of the cell cycle is the centrosome replicated?
S phase Synthesis phase (S): This is where a cell will replicate its genome in preparation of an ensuing cell division. Cells that have a centrosome will also duplicate the centrosome in this stage.
When does cell division occur in bacteria and archaea?
Simultaneously with DNA replication Binary fission is how archaea, bacteria, and certain organelles (mitochondria and chloroplasts) reproduce. The mechanics of mitosis and binary fission are a little different. Mitotic cells will replicate their genome during the S phase of interphase. On the other hand, organisms (or organelles) that reproduce via binary fission will replicate their genome as cell division is taking place (replication of DNA and division occur simultaneously).
Which of the following will occur as a cell grows bigger?
Surface area to volume ratio decreases
Consider a cell whose volume is too great for the cell membrane to hold. What functional limitation encourages cell division in this case, and why?
Surface to volume ratio; cellular exchange
During which phase(s) of meiosis do nuclear envelopes reform?
Telophase I and telophase II During telophase I, the meiotic spindle disappears as nuclear envelopes form around each set of homologs at either pole. Then, the nucleoli will regenerate inside of each nucleus, and the haploid number of dyad chromosomes will decondense back into chromatin in preparation for meiosis II. Telophase II reforms a nuclear envelope around each chromosome set, creating two new daughter nuclei. After this, the chromosomes will decondense back into chromatin, and nucleoli will reappear in each nucleus.
What does the term "ploidy" refer to?
The # of chromosomes sets found in a cell For example, haploid cells contain one set of chromosomes, while diploid cells contain two sets.
Microtubules in eukaryotes are polymers of which protein?
Tubulin Microtubules in eukaryotes are polymers of the protein tubulin, and have an important role in cell structure and division.
Which of the following describes homologous chromosome pairs?
Two different copies of the same chromosome in a diploid organism Homologous chromosome pairs are the two 'different copies' of the same chromosome in a diploid organism. One copy is given by the mother and the other copy given by the father. In the illustration below, the diploid organism has four total chromosomes, i.e. two sets of homologous pairs. The mother has contributed one chromosome #1, and one chromosome #2 (blue). The father has contributed one chromosome #1, and one chromosome #2 (red). The set (one red, one blue) of chromosome #1 are a homologous pair (homologs); the set (one red, one blue) of chromosome #2 are a homologous pair (homologs).
Each bivalent contains which of the following?
Two homologous chromosomes Synapsis describes the process of homologous dyads pairing up to form bivalents or tetrads, via the synaptonemal complex. The synaptonemal complex is a protein structure that temporarily forms between homologous dyads. Bivalents (or tetrads) are a pair of two homologous dyads, each containing a pair of sister chromatids.
How many centrioles make up one centrosome, and how are they oriented?
Two; right angles to each other A centrosome is an organelle found within animal cells that is a type of MTOC. Centrosomes are proteins made up of two centrioles at right angles to one another.
What problem does a low genome to volume ratio cause in a cell?
Underproduction of regulatory proteins G/V encourages cell division when the volume of the cell grows to a size that places too many demands on the cell's genome, i.e. its ability to make adequate proteins. The genome codes for all the functional proteins a cell needs to live. If the cell becomes too large relative to the size of the genome, it will limit its growth.
What is the shortest phase of mitosis?
anaphase
What is the correct order of mitosis?
prophase, metaphase, anaphase, telophase There are four main phases in mitosis that we'll focus on for the DAT: prophase, metaphase, anaphase, and telophase. Sometimes cytokinesis is lumped into mitosis, but really it is considered a separate process.
