https://padlet.com/brandyabell/aoqd4qnqk92ef3s5 en-us 2022-11-21 08:42:15 UTC 2022-12-23 16:45:32 UTC hello@padlet.com brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427606692 2022-12-22 17:54:29 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427606692 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427609641 2022-12-22 18:01:35 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427609641 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427741784 Mitosis, by definition, is the period of the cell cycle at which the duplicated chromosomes are distributed into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase(Fowler,Raush,&Wise, 2021). 
Interphase is the period of the cell cycle leading up to mitosis, and is divided into three stages: the first stage of interphase is called the G1 Phase and there is little change within the cell happening at this point. However, the cell is very active at the biochemical level during this phase as it is busy accumulating the building blocks of chromosomal DNA and all of the associated proteins, as well as accumulating enough energy reserves in order to replicate each chromosome in the nucleus(Fowler, S., Roush, R., & wise, J., 2021). 
The second phase of Interphase is S Phase, and this is the phase where DNA replication occurs and two identical copies of each chromosome, called sister chromatids, are made. These sister chromatids are are firmly attached at the centromere region of the nucleus. The centromere, along with the chromosomes, are duplicated at this stage. The two centromeres will eventually become the mitotic spindle, which is the part of the cell that controls the chromosomal movement during mitosis. The centrosome consists of a pair of centrioles which are rod-like structures that are at right angles to one another that help organize cell division. Centrioles are not present in many eukaryotic species, for example, plants and most fungi(Fowler, S., Roush, R., & Wise, J., 2021). 
The third and final phase of Interphase is the G2 Phase where the cell replenishes its energy stores and also synthesizes the proteins necessary for chromosome manipulation(Fowler, S., Roush, R., & Wise, J., 2021). Some of the cell's organelles are duplicated and the cytoskeleton is dismantled in order to provide resources to create the mitotic spindle. Also, there may be additional cell growth during this phase. The final mititic phase preparations need to be completed before the cell can enter the first stage of mitosis(Fowler, S., Roush, R., & Wise, J., 2021).]]> 2022-12-23 01:05:47 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427741784 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427744723 2022-12-23 01:11:14 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427744723 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427835565 Mitosis is divided into a series of phases which are as follows: prophase, prometaphase, metaphase, anaphase, and telophase. Once a cell has gone through all five of these stages then the division of the cell's nucleus has occured(Fowler, S., Raush, R., & Wise, J., 2021). 
The first phase is prophase and in this phase several different things need to occur in order to provide access to the chromosomes in the nucleus. The nuclear envelope will start to break into small vesicles, and the Golgi apparatus and the endoplasmic reticulum fragment and disperse to the periphery of the cell(Fowler, Raush, & Wise, 2021). The nucleolus disappears and the centrosomes will start to move to opposite poles of the cell. The microtubules that will form the basis of the mitotic spindle will extend between the centrosomes which, in turn, will push them farther apart as the microtubule fibers grow longer. The sister chromatids will begin to coil more tightly and become visible under a light microscope(Fowler, S., Raush, R., & Wise, J., 2021).
The second phase is called prometaphase and this is the phase where the many processes that were started in the first phase continue to advance and culminate in the formation of a connection between the cytoskeleton and the chromosomes themselves(Fowler, Raush, and Wise, 2021). The remains of the nuclear envelope will now disappear and the mitotic spindle will continue to develop as more microtubules assemble and stretch across the length of what was the nuclear area. Chromosomes become more condensed as each sister chromatid attaches to mitotic spindle microtubules at the centromere with the help of a protein complex called the kinetochore.
The third phase is called metaphase and this is where all of the chromosomes are lined up on a plane called the metaphase plate or the equatorial plane, which is halfway between the two poles of the cell. The sister chromatids are still tightly attached to each other and at this time the chromosomes are as tightly condensed as possible. 
The fourth phase is called anaphase and this is the phase where the sister chromatids at the equatorial plane are split at the centromere. Each chromatid is now called a chromosome is rapidly pulled to the centrosome to which its microtubule was attached. The cell becomes very visibly elongated as the non-kinetochore microtubules slide against each other at the equatorial plate where they overlap now. 
The fifth and final phase is called telophase and this is the phase where all of the events that set up the duplicated chromosomes for mitosis in the first three phases is reversed. The chromosomes reach the opposite poles and begin to unravel or decondense. The mitotic spindles are broken down into monomers that will be used to assemble cytoskeleton components for each new daughter cell and nuclear envelopes form around the chromosomes(Fowler, S., Raush, R., & Wise, J., 2021).]]> 2022-12-23 04:29:40 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427835565 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427946714 Cytokinesis is the second part of the mitotic phase where cellular division is completed by the physical separation of the cytoplasmic contents into two daughter cells. Whereas mitosis is similar for most eukaryotes, cytokinesis is very different for eukaryotes that have cell walls like plant cells, for example. In animal cells that do not have cell walls, cytokinesis begins following the beginning of anaphase with a contractible ring made up of actin filaments forms just inside the plasma membrane where the former metaphase plate was. These actin filaments pull the equator, or center, of the cell inward, creating a fissure or crack that is called the cleavage furrow(Fowler, S., Raush, R., & Wise, J., 2021). This cleavage furrow grows deeper as the actin ring contracts, until eventually the plasma membrane and the cell are contracted in two. 
In plant cells this cleavage furrow cannot form because the walls that surround the plasma membrane are too rigid. A whole new cell wall must form between the daughter cells instead. During interphase the Golgi apparatus starts to accumulate enzymes, structural proteins, and glucose molecules before breaking into vesicles and dispersing throughout the dividing cell(Fowler, Raush, & Wise, 2021). 
During telophase these Golgi vesicles move with the help of microtubules to gather at the center of the metaphase plate. At the metaphase plate, the vesicles fuse from the center toward the cell walls forming a structure called a cell plate. As the cell plate grows via more vesicles fusing, until it merges with the cell wall at the periphery of the cell. Enzymes will now use the glucose that has accumulated between the layers of the membrane to build a new cell wall made of cellulose. The golgi membranes will now become the plasma membrane on either side of thois new cell wall. 
Cells in the Go phase are cells that are not actively preparing for cell division. The cell is in an inactive stage having exited the cellular division cycle. Some cells enter this phase temporarily until some sort of trigger begins the onset of the cellular division cycle and there are some cells that are mature and remain in this phase permanently. ]]> 2022-12-23 10:19:38 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427946714 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427966082 Meiosis, by definition, is a nuclear division that results in four haploid cells(Fowler, Raush, & Wise, 2021). Meiosis is similar to mitosis in some ways and in others it can be very different. One of the biggest differences between the two is that meiosis occurs as a result of sexual reproduction, whereas mitosis does not. Sexual reproduction requires a process called fertilization which is a union of two cells from two individual organisms. If both of these cells contain a set of chromosomes then the new cell will contain two sets of chromosomes. The number of sets of chromosomes in a cell is called the cell's ploidy level. Haploid cells have only one set of chromosomes, whereas diploid cells have two sets. In order for the reproductive cycle to continue, the diploid cell must reduce the number of chromosome sets in every generation. This is where a nuclear division called meiosis occurs. 
Most animal and plant cells are diploid, containing two chromosome sets in each somatic cell which is the nonreproductive cells of a multicellular organism(Fowler, Raush, & Wise, 2021). In somatic cells, the nucleus contains two copies of each chromosome that are called the homologous chromosomes. Somatic cells are sometimes called the "body" cells. Homologous chromosomes are matched pairs of chromosomes that contain genes for the same traits in identical locations along their length. Diploid organisms inherit one copy of each homologous chromosome from each parent; all together they are considered a full set of chromosomes. In animals, haploid cells that contain only a single copy of each homologous chromosome are found only within gametes. These gametes fuse with another haploid gamete to produce a diploid cell(Fowler, Raush, & Wise, 2021). This nuclear division that forms haploid cells is called meiosis. ]]> 2022-12-23 11:23:10 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427966082 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427985253 In meiosis, the starting nucleus is always diploid and the ending nuclei are haploid. In order to reduce the chromosomal number, meiosis has one round of chromosome duplication and two rounds of nuclear division. In Meiosis 1 the number of chromosome sets is reduced and this is also where the genetic information gets mixed in order to create recombinant chromosomes.
Interphase in meiosis also consists of 3 phases; G1, S, and G2. The G1 or first phase of interphase focuses on cell growth. The S phase, or second phase of interphase, the DNA of the DNA of the chromosomes is replicated, and in G2, or the third phase of interphase, the cell undergoes the final preparations for meiosis(Fowler, Raush, & Wise, 2021).

]]> 2022-12-23 12:32:42 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427985253 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427985969 2022-12-23 12:35:05 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2427985969 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428018890 Early in prophase 1 the chromosomes can be clearly seen using a microscope. Once the nuclear envelope begins to break down, the proteins that are associated with homologous chromosomesbring the pair tightly close to each other. This tightly close-knit pairing is called synapsis. Synapsis is where the genes on the chromatids of the homologous chromosomes are lined very precisely with each other. Chromosome parts are exchanged between non-sister homologous chromatids which is called crossing over. This process becomes visible after the exchange as chiasmata(Fowler, S., Raush, R., & Wise, J., 2021). As prophase 1 advances, the close-knit connection between homologous chromosomes begins to break down and the chromosomes continue to condense while the homologous chromosomes stay attached to each other at the chiasmata. The number of chiasmata varies depending on the species and length of the chromosome. When prophase 1 ends, the pairs are held together only at the chiasmata and are called tetrads because the four sister chromatids of each pair of homologous chromosomes have now become visible. What happens during the crossover is the first source of genetic variation produced during meiosis(Fowler, S., Raush, R., & Wise, J., 2021). One single crossover event between two non-sister chromatids leads to an even exchange of DNA that s not exactly the same but close between a maternal and paternal chromosome. Now when one of those sister chromatids is moved into a gamete it will carry DNA from both parents. The recombinant sister has a combination of maternal and paternal genes that it did not have before the crossover. 
The key event that happens during prometaphase 1 is the attachment of the microtubule spindle fibers to the kinetochore proteins at the centromeres. The microtubules made from centrosomes at opposite ends of the cell now grow toward the middle of the cell. At the end of prometaphase 1 each tetrad is attached to microtubules from both ends with one homologous chromosome attached to one end and the other homologous chromosome attached to the other end. These homologous chromosomes are still attached at chiasmata. Also, the nuclear membrane is entirely broken down at this phase. ]]> 2022-12-23 14:14:22 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428018890 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428034833 During metaphase 1 the homologous chromosomes are arranged in the center of the cell with the kinetochores facing opposite ends. The orientationof each pair of homologous chromosomes at the center of the cell is random. This random assortment is called independent assortment actually and is the physical basis for the generation that carries the second form of genetic variation in offspring. Imagine that the homologous chromosomes of a sexually reproducing organism are originally inherited as two separate sets, one from each parent. In metaphase 1 these pairs line up at the halfway point between either end of the cell. Since there is an equal chance that a microtubule will encounter a maternal or paternal inherited chromosome, the arrangement of the tetrads at the metaphase plate is random. In each cell that undergoes meiosis, the arrangement of the tetrads is different, and the number of variations will depend on the number of chromosomes per set. There are two possibilities for orientation for each tetrad and whatever that number may be(depending on what type of cell it is whether it be human, animal, etc.), that number does not include the variability previously created in the sister chromatids by crossover(Fowler, Raush, & Wise, 2021). This means that it is very highly unlikely that any two haploid cells that were created durting meiosis will have the same genetic makeup. ]]> 2022-12-23 15:01:13 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428034833 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428059571 In anaphase 1 the spindle fibers pull the joined chromosomes apart. The sister chromatids are still tightly knit together at the centromere. The chiasmata connections are what's broken during this phase because the fibers that are attached to the fused kinetochores pull the homologous chromosomes apart(Fowler, Raush, & Wise, 2021). 
In telophase 1 the separated chromosomes appear at opposite ends of the cell and, depending on the species, the remaining occurrences during this phase may not even occur. Some organisms see a decondensing in the chromosomes and nuclear envelopes form around the chromatids in this phase. 
Cytokinesis, which as we know is the physical separation of the cytoplasm and all of its contents into two daughter cells, occurs without the reformation of the nuclei in other organisms. In almost every species, cytokinesis separates the cell contents through a cleavage furrow or a cell plate that will ultimately lead to the formation of cell walls that will separate the two daughter cells . On each end there is just one member of each pair of homologous chromosomes so there is only one full set of chromosomes present. The cells are considered to be haploid because there is only one chromosome set even though there duplicate copies of this set since each homolog still has two sister chromatids that are still attached to each other(Fowler, Raush, & Wise, 2021). Even though the sister chromatids were once duplicates of the same chromosome, they are not identical at this point anymore because of crossovers. ]]> 2022-12-23 16:17:59 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428059571 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428066215 In meiosis 2 the connected sister chromatids will be split and will become four haploid cells. Some cells will enter a brief interphase also called interkinesis, that does not have an S phase, before beginning the steps of meiosis 2. Chromosomes are not duplicated during this phase and the two cells produced in meiosis 1 undergo meiosis 2 at the same time. 
In prophase 2 the chromosomes will once again condense and if nuclear envelopes were formed again, they will break apart into vesicles again. The centrosomes that were duplicated during interkinesis move toward opposite ends of the cell again and new spindles will be formed. 
In prometaphase 2 the nuclear envelopes will be completely broken down again and the spindle will become fully formed(Fowler, S., Raush, R., & Wise J., 2021). Each of the sister chromatids will form a kinetochore that will attach to microtubules from opposite ends of the cell. 
In anaphase 2 the sister chromatids are pulled apart by these spindle fibers and will move toward opposite ends of the cell. 
In telophase 2 the chromosomes that are now at opposite ends of the cell will begin to decondense and nuclear envelopes will form around the chromosomes. Cytokinesis will separate these two cells into four genetically different haploid cells. At this point in the cellular division the nuclei in these new cells have only one copy of the single set of chromosomes. What makes these new cells genetically unique is the random assortment of maternal and paternal homologs and also because of recombination of the maternal and paternal segments of chromosomes and their sets of genes that occurs during crossover(Fowler, Raush, & Wise, 2021). ]]> 2022-12-23 16:37:53 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428066215 brandyabell https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428068238 Fowler, S., Raush, R., & Wise, J.(2021, January 12). Concepts of biology. Open Stax College. 
https://www.genome.gov/genetics-glossary/mitosis
https://medium.com/@biologynotes/meiosis-16a31fec3838
https://natural-universe.net/the-scientific-view--of-the-geological-present/what-biochemistry-and-cellular-biology-tell-us/cell-division-the-cell-cycle
https://www.britannica.com/science/cell-biology/meiosis]]> 2022-12-23 16:45:32 UTC https://padlet.com/brandyabell/aoqd4qnqk92ef3s5/wish/2428068238