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Cell Division


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Cell Division
Two phases are nuclear division then cytokinesis
nuclear division divides the genetic material in the nucleus while this process divides the cytoplasm
Nuclear division where the nucleus is dirvided into two genetically identical daughter cells
Nuclear division in which this is a reduction division, producing daughter cells that contain half the genetic information of the parent cell
Genetic material that turns into chromosomes int he first step of either mitosis or meiosis
tightly coiled bodies of chromatin in the first stage of mitosis or meiosis, and each one is made of two identical halves called sister chromatins
Sister Chromatids
th two parts of each chromosome and each chromatid consists of a single, tightly coiled molecule of DNA, and they are both joined at the centromere
Where sister chromatids are joined
Diploid Cells
When there are two copies of every chromosome dorming a pair of homologous chromosomes
Homologous Chromosomes
In diploid cells, the pair of two copies of every chromosome, in which one homologue originiated from the maternal parent and the other from the paternal.
How many chromosomes humans have
Humans have 46 chromosomes, 23 homologous pairs and a total of 92 chromatids
Visible within the nucleus when the cell is not dividing
Mirctotubule organizing centers (MTOC and also called centrosomes in animals)
two of these reside outside of the nucleus and they lie adjacent to one another. In animals, each one contains a pair of centrioles and these features are characteristic of interphase.
In animals, each MTOC contains a pair of these
the non dividing period of teh cell cyle in whcih MTOC's and centrioles and etc. are featured
The Cell Cycle
Interphase includes G1 (growth), S (growth and duplication of DNA), G2 (growth and preparation for cell division), and then the steps of mitosis
Mitosis steps
prophase, metaphase, anaphase, and telophase
1st stage of mitosis in which the nucleoli disappear and the chromatin condenses into chromosomes, then the nuclear envelop breaks down, then the mitotic spindle is assembled (MTOC's move apart to opposite ends, tubulin is added for length, microtubules connect to a specialized region called the kinetochore and chromosomes move
Mitotic Spindle
Development of this begins as the MTOC's move apart to opposite ends/poles of the nucleus, then as they move apart, mirotubules develop from each MTOC, increasing in length by the addition of tubulin units to the microtuble ends away from the MTOC
Specialized region in the centromere called a kinetochore where microtubules are attached
Completed spindle also includes...
the mircotubules from each MTOC that overlap at the center of the spindle and do not attach to the chromosomes
begins when the chromosomes are distributed across the metaphase plate and ends when the microtubules, still attached to the kinetochores, pull each chromosome apart into two chromatids. Each is complete with a centromere and a kinetochore and now it is called a chromosome (but always count number of centromeres for the number of chromosomes)
Metaphase Plate
a plane lying between the two poles of the spindle where the chromosomes are distributed
begins after the chromosomes are separated into chromatids and now the microtubules connected to the chromatids (now chromosomes) shorten, effectively pulling the chromosomes to opposite poles. They shorten as tubulin units are uncoupled at the chromosome ends. Overlapping microtubules push the poles farther apart and at the end, each pole has a complete set of chromosomes
concludes the nuclear division. During this phase, a nuclear envelop develops around each pole, forming two nuclei. The chromosomes with each of these nuclei disperse into chromatin and the nucleoli reappear. Cytokineses occurs at the same time, dividing the cell into two. In animals, microfilaments form a ring inside the plasma mebrane between the two newly forming nuclei, and as they shorten, they act as purse strings to pull the plasma membrane into the center, dividing it in two.
Cleavage Furrow
the groove that forms as the purse strings (microtubules) during Animal cytokineses are tightened
Cell Plate
in plants' cytokinesis, vesicles orignating from Golgi bodies migrate to the plane between the newly forming nuclei and fuse to form a cell plate whcih subsquently becomes the plasma membrane for the two daughter cells, and later cell walls develop
Cell Cycle (2)
the time span from one cell division through G1, S, and G2 (in which the cell is growing through all phases)
In prophase I, when homologous chromosomes pair and then corresponding regions along nonsister chromatids form close associations where genetic material is exchanged.
a group of four chromatids which is a pair of homologous chromosomes during prophase I
same as tetrads
Chiasmata, chiasma
during synapsis, corresponding regions along nonsister chromatids form these close associations which are sites where genetic material is exchanged between nonsister homologous chromatids in a process called CROSSING OVER
Synaptonemal Complex
A tetrad together with chiasmata and crossover events
Metaphase I
homologous pairs of chromosomes are apread across the metaphase plate and microtubules extending from one pole are attached to the kinetochore of one member of each homologous pair. Microtubules from the other pole are connected to the second member of each homologous pair.
order of mitosis
Anaphase I
begins when homologues within tetrads uncouple as they are pulled to opposite poles
Telophase I
the chromosomes have reached their respective poles and a nuclear membrane develops around them. Each pole forms a new nucleus that will have half the chromosomes, but each chromosome will contain two chromatids. since daughter nuclei will have half the number of chromosomes, cells that eventually form will be HAPLOID
Prophase II
the nuclear envelop disappears and the spindle develops. there are no chiasmata and no crossing over of genetic material
Metaphase II
the chromosomes align singly on the metaphase plate and single alignment of chromosomes is exactly what happens in mitosis except that now there is only half the number of chromosomes
Anaphase II
begins as each chromosome is pulled apart into two chromatids by the microtubules of the spindle apparatus. The chromatids (now chromosomes) migrate to their respective poles. Again this is exactly what happens in mitosis but with half the chromosomes
Telophase II
the nuclear envelop reappears at each pole and cytokinesis occurs. The end result of meiosis is four haploid cells, and each cell contains half the number of chromosomes and each only has one chromatid. and later in interphase, a second chromatid in each chromosome is replicated but it will still have only half the number of chromosomes
or fertilization, the fusing of an egg and a sperm
diploid cell after fertilization
haploid cells that divide by mitosis to become a multicellular haploid structure, the gametophyte
What is produced after a spore goes through mitosis
Mitotic gametes that divide by meiosis to become haploid spores
Genetic Recombination
orginates from crossing over, independent assortment of homologues, and random joining of gametes
Crossing Over
during Prophase I, nonsister chromatids of homologous chromosomes exchange pieces of genetic material. As a result, each one no longer represents a single parent
Independent assortment of homologues
During metaphase I, tetrads of homologous chromosomes seperate into chromosomes that go to opposite poles. whcih chromosome goes to which pole depends on the orientation of a tetrad at the metaphase plate. This is random for each tetrad.
Random Joining of Gametes
whcih sperm fertized which egg is to a large degree a random eventm however, this event may be affected by the genetic composistion of a gamete, for example, some sperm may be faster swimmers and have a better chance of fertilizing the egg
surface to volume ratio
when this becomes large, there is a large surface area relative to volume and a cell can be efficient, but when it is small, it needs to divide
genetic material in the nucleus which controls the cell by producing substances which make enzymes and other biosynthetic substances and as the cell grows, it needs more genomes, so it divides
genome-to-volume ratio
when this decreases, the cell's size exceeds the ability of its genome to produce sufficient amounts of materials for regulating cellular activities, so it divides
density-dependent inhibition
when cells stop dividing because the surrounding cell density reaches a certain maximum. (Some cells will rearely divide once they have matured)

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