2.Know the mitosis and meiosis cell cycles in complete detail. This includes the names of the stages and what happens to the chromosomes during each stage. What kinds of cells does each process produce? Which is the ‘reduction division’ and what does this mean? How many cell divisions are in each cell cycle? Know when chromatids separate in meiosis. Do they separate in mitosis and if so when does this happen?
MITOSIS
Mitosis is the process in which a eukaryotic cell nucleus splits in two, followed by division of the parent cell into two daughter cells. The word "mitosis" means "threads," and it refers to the threadlike appearance of chromosomes as the cell prepares to divide. Early microscopists were the first to observe these structures, and they also noted the appearance of a specialized network of microtubules during mitosis. These tubules, collectively known as the spindle, extend from structures called centrosomes — with one centrosome located at each of the opposite ends, or poles, of a cell. As mitosis progresses, the microtubules attach to the chromosomes, which have already duplicated their DNA and aligned across the center of the cell. The spindle tubules then shorten and move toward the poles of the cell. As they move, they pull the one copy of each chromosome with them to opposite poles of the cell. This process ensures that each daughter cell will contain one exact copy of the parent cell DNA.
What Are the Phases of Mitosis?
Mitosis consists of five morphologically distinct phases: prophase,
prometaphase, metaphase, anaphase, and telophase. Each phase
involves characteristic steps in the process of chromosome
alignment and separation. Once mitosis is complete, the entire cell
divides in two by way of the process called cytokinesis
What Happens during Prophase?
Prophase is the first stage in mitosis, occurring after the
conclusion of the G2 portion of interphase. During prophase, the
parent cell chromosomes — which were duplicated during S phase —
condense and become thousands of times more compact than they were
during interphase. Because each duplicated chromosome consists of
two identical sister chromatids joined at a point called the
centromere, these structures now appear as X-shaped bodies when
viewed under a microscope. Several DNA binding proteins catalyze
the condensation process, including cohesin and condensin. Cohesin
forms rings that hold the sister chromatids together, whereas
condensin forms rings that coil the chromosomes into highly compact
forms.
The mitotic spindle also begins to develop during prophase. As the cell's two centrosomes move toward opposite poles, microtubules gradually assemble between them, forming the network that will later pull the duplicated chromosomes apart.
What Happens during Prometaphase?
When prophase is complete, the cell enters prometaphase — the
second stage of mitosis. During prometaphase, phosphorylation of
nuclear lamins by M-CDK causes the nuclear membrane to break down
into numerous small vesicles. As a result, the spindle microtubules
now have direct access to the genetic material of the cell.
Each microtubule is highly dynamic, growing outward from the centrosome and collapsing backward as it tries to locate a chromosome. Eventually, the microtubules find their targets and connect to each chromosome at its kinetochore, a complex of proteins positioned at the centromere. The actual number of microtubules that attach to a kinetochore varies between species, but at least one microtubule from each pole attaches to the kinetochore of each chromosome. A tug-of-war then ensues as the chromosomes move back and forth toward the two poles.
What Happens during Metaphase and Anaphase?
As prometaphase ends and metaphase begins, the chromosomes align
along the cell equator. Every chromosome has at least two
microtubules extending from its kinetochore — with at least one
microtubule connected to each pole. At this point, the tension
within the cell becomes balanced, and the chromosomes no longer
move back and forth. In addition, the spindle is now complete, and
three groups of spindle microtubules are apparent. Kinetochore
microtubules attach the chromosomes to the spindle pole; interpolar
microtubules extend from the spindle pole across the equator,
almost to the opposite spindle pole; and astral microtubules extend
from the spindle pole to the cell membrane.
Metaphase leads to anaphase, during which each chromosome's
sister chromatids separate and move to opposite poles of the cell.
Enzymatic breakdown of cohesin — which linked the sister chromatids
together during prophase — causes this separation to occur. Upon
separation, every chromatid becomes an independent chromosome.
Meanwhile, changes in microtubule length provide the mechanism for
chromosome movement. More specifically, in the first part of
anaphase — sometimes called anaphase A — the kinetochore
microtubules shorten and draw the chromosomes toward the spindle
poles. Then, in the second part of anaphase — sometimes called
anaphase B — the astral microtubules that are anchored to the cell
membrane pull the poles further apart and the interpolar
microtubules slide past each other, exerting additional pull on the
chromosomes
During mitosis, several types of microtubules are active. The motor
proteins associated with the interpolar microtubules drive the
assembly of the spindle. Note the other types of microtubules
involved in anchoring the spindle pole and pulling apart the sister
chromatids.
What Happens during Telophase?
During telophase, the chromosomes arrive at the cell poles, the
mitotic spindle disassembles, and the vesicles that contain
fragments of the original nuclear membrane assemble around the two
sets of chromosomes. Phosphatases then dephosphorylate the lamins
at each end of the cell. This dephosphorylation results in the
formation of a new nuclear membrane around each group of
chromosomes.
When Do Cells Actually Divide?
Cytokinesis is the physical process that finally splits the parent
cell into two identical daughter cells. During cytokinesis, the
cell membrane pinches in at the cell equator, forming a cleft
called the cleavage furrow. The position of the furrow depends on
the position of the astral and interpolar microtubules during
anaphase.
The cleavage furrow forms because of the action of a contractile ring of overlapping actin and myosin filaments. As the actin and myosin filaments move past each other, the contractile ring becomes smaller, akin to pulling a drawstring at the top of a purse. When the ring reaches its smallest point, the cleavage furrow completely bisects the cell at its center, resulting in two separate daughter cells of equal size.
Conclusion
Mitosis is the process of nuclear division, which occurs just prior
to cell division, or cytokinesis. During this multistep process,
cell chromosomes condense and the spindle assembles. The duplicated
chromosomes then attach to the spindle, align at the cell equator,
and move apart as the spindle microtubules retreat toward opposite
poles of the cell. Each set of chromosomes is then surrounded by a
nuclear membrane, and the parent cell splits into two complete
daughter cells.
MEIOSIS
Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. During reproduction, when the sperm and egg unite to form a single cell, the number of chromosomes is restored in the offspring.
Meiosis begins with a parent cell that is diploid, meaning it has two copies of each chromosome. The parent cell undergoes one round of DNA replication followed by two separate cycles of nuclear division. The process results in four daughter cells that are haploid, which means they contain half the number of chromosomes of the diploid parent cell.
Meiosis has both similarities to and differences from mitosis, which is a cell division process in which a parent cell produces two identical daughter cells. Meiosis begins following one round of DNA replication in cells in the male or female sex organs. The process is split into meiosis I and meiosis II, and both meiotic divisions have multiple phases. Meiosis I is a type of cell division unique to germ cells, while meiosis II is similar to mitosis.
Meiosis I, the first meiotic division, begins with prophase I. During prophase I, the complex of DNA and protein known as chromatin condenses to form chromosomes. The pairs of replicated chromosomes are known as sister chromatids, and they remain joined at a central point called the centromere. A large structure called the meiotic spindle also forms from long proteins called microtubules on each side, or pole, of the cell. Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination. Recombination is a process that breaks, recombines and rejoins sections of DNA to produce new combinations of genes. In metaphase I, the homologous pairs of chromosomes align on either side of the equatorial plate. Then, in anaphase I, the spindle fibers contract and pull the homologous pairs, each with two chromatids, away from each other and toward each pole of the cell. During telophase I, the chromosomes are enclosed in nuclei. The cell now undergoes a process called cytokinesis that divides the cytoplasm of the original cell into two daughter cells. Each daughter cell is haploid and has only one set of chromosomes, or half the total number of chromosomes of the original cell.
Meiosis II is a mitotic division of each of the haploid cells produced in meiosis I. During prophase II, the chromosomes condense, and a new set of spindle fibers forms. The chromosomes begin moving toward the equator of the cell. During metaphase II, the centromeres of the paired chromatids align along the equatorial plate in both cells. Then in anaphase II, the chromosomes separate at the centromeres. The spindle fibers pull the separated chromosomes toward each pole of the cell. Finally, during telophase II, the chromosomes are enclosed in nuclear membranes. Cytokinesis follows, dividing the cytoplasm of the two cells. At the conclusion of meiosis, there are four haploid daughter cells that go on to develop into either sperm or egg cells.
2.Know the mitosis and meiosis cell cycles in complete detail. This includes the names of the...
Name: Mitosis vs. Melosis Period Date: QUESTION 1 concept map comparing mitosis and meiosis. Use the following te rms, each term can be diploid cell, one cell division, four haploid cells, parent ce cell divisions, body cell, same, chromosomes & cell, half, two diploid cells, forms haploid cell Use used one or more times: ll, two 2. Define homokgous chromosome 3. Define sister chromatids 4. Describe 2 parts of meiosis that are similar to mitosis. a. b. 5. Identify whether...
Meiosis is composed of two chromosomal division called Meiosis I and Meiosis II. Each of the two divisions consists of Prophase, Prometaphase, Metaphase, Anaphase and Telophase and each of these phases is designated I or II according to which division it is a part of. Be sure you know what happens in each phase in regard to the chromosomes, chromatids, spindles and the nuclear envelope. During which phase does synapsis occur and crossing over begin? And in which division, Meiosis I or Meiosis II...
Compare mitosis and meiosis by filling in the chart below. Meiosis Mitosis Characteristic Are daughter cells genetically identical or different from the parent? Involves how many cell divisions? Produces how many daughter cells? Produces haploid or diploid cells? Produces what type of cell? Sister chromatids or homologous chromosomes separate? What are the functions of the cells produced? 05 Answer the following Explain how segregation of chromosomes during meiosis can generate four types of gametes (assume four chromosomes, two homologous pairs)...
SUMMARY – COMPARE MITOSIS AND MEIOSIS 1. What structures are present in the phases? How many? (Use numbers like 2n, 1n, etc., and terms like dyads, tetrads, replicated chromosomes, chromatids, chromosomes, ...) Phase Mitosis Meiosis I Meiosis II Prophase Metaphase Anaphase Telophase Cytokinesis Ploidy level after all divisions of 2n cell Number & type of cells produced by division(s) Function in life cycle
Mitosis and Meiosis. 1. Draw a cell where 2n = 6 in each phase of Mitosis, Meiosis 1, and Meiosis 2. Be sure to clearly indicate what is going on with the 1-nuclear envelope, 2-centrosomes, 3-chromosomes in each of the stages. 2. For a diploid organism where 2n = 16, please indicate the number of chromosomes and chromatids at each of the Mitosis, Meiosis 1, Meiosis 2 stages.
How do the results of meiosis and mitosis differ in terms of chromosome numbers? Fill in the diagrams with the appropriate chromosome number (total number of chromosomes and/or sister chromatids!) by assuming that each original cell (at the top of the diagram) represents a human cell with a diploid number of chromosomes in G2 stage of the cell cycle. mitosis meiosis O first meiotic division first meiotic division 2nd meiotic division O OO O
all these questions have more than one correct answers 1) Meiosis & mitosis have similarities as well as differences. Which of the following represent similarities? a) Both increases genetic variation b) Both change in chromosomes number in daughter cells c) Both only occur in eukaryotes D) DNA replication must occur prior to both e) Both make use of a spindle to separate chromatids 2) Meiosis is a special form of cell division. Select any of the following that applies to...
Activity 1: Observation of Mitosis in an Onion and a Whitefish Instructions: View the images in Table 1 and Table 2 of the Activity 1 Page to complete blanks below Table 1: Stages of the Cell Cycle in Onion Root Tip Table 2: Stages of Mitosis in Whitefish Blastula *Name Each Stage *Name Each Stage (a) (b) (b) (c) (c) (d) (d) (e) *To name the stages above, choose from: Interphase, Prophase. Metaphase, Anaphase or Telophase/Cytokinesis Identify the number in...
HILMIUSIS AND MEIOSIS 1. What structures are present in the phases? How many? (Use numbers like 2n, 1n, etc., and terms like dyads, tetrads, replicated chromosomes, chromatids, chromosomes,...) Mitosis Phase Prophase Meiosis Meiosis II Metaphase Anaphase Telophase Cytokinesis Ploidy level after all divisions of 2n cell Number & type of cells produced by division(s) Function in life cycle
4. Complete the following table. Mitosis Meiosis MitosisMeiosis Synapsis (Yes or no Crossing over (When) Anaphase I results When do centromeres divide No. of divisions No. of cells resulting Anaphase II results No. of chromosomes in daughter cells Assume cell divisions are occurring on the arrows in this gen- eralized plant life cycle. Show where mitosis and meiosis occur. 5. Multicellular diploid plant Spore Multicellular haploid plant Starting with a diploid cell (A) that has 2 homologous chromo- somes (2N-2),...