It is usually double stranded. A (Adenine) pairs with T (Thymine). C (Cytosine) pairs with G (Guanine). When cell division occurs, the DNA is double for both daughter cells. The two strands unwind, unzip and separate in search for a new strand to interact with and form a cell.
It represents nature's solution to the problem of chromosome doubling that would occur, if two diploid cells, i.e. two cells with a double set of chromosomes would fuse. Accordingly does meiosis produce haploid germ cells, with maternal and paternal germ cell fusing at fertilization and thus generating a diploid fusion product, the zygote. Meiosis is made up by two subsequent processes, both of which resemble mitosis. In the first process are the homologous chromosomes separated.
The centrioles migrate to opposite ends of poles of the cell. Microtubules develop and form a star-shaped structure called the spindle. The nucleolus and the nuclear envelope disappear leaving the chromosomes. Prophase in Meiosis 1 is similar to prophase in mitosis, as the chromosomes become visible, shorten and widen but it different because they associate in their homologous pairs. Organisms consist of two sets of chromosomes where any two chromosomes, which decide the same characteristic, are called a homologous pair.
Meiosis unlike mitosis has two cell divisions, Meiosis I and Meiosis II. In prophase I of meiosis I, the chromosomes begin by pairing with its homolog and this is also where crossing over occurs. In this stage just like prophase in mitosis the nuclear envelope breaks down and the mitotic spindle begins to develop as well. In Metaphase I the homologue chromosomes line up at the metaphase plate and the kinetochore microtubules attach to both ends of the chromosome. In anaphase I the homologs move to opposite ends of the poles and the homologs also begin to separate as well.
The microtubule spindles attach to the kinetochores in metaphase II, causing the chromosomes to line up, and at the start of anaphase II, the remaining cohesins at the centromere break down, so that the sister chromatids are able to separate and move to opposite ends of the cell. (Alberts et al., 2008.) They then undergo telophase and cytokinesis to produce four haploid cells. (Lodish et al., 2008.) Mitosis and meiosis are similar methods of cell division, as both produce daughter cells.
Telophase I and cytokinesis: The chromosomes finished their move to the opposite poles of the cell. At each pole of the cell a full set of chromosomes get together. A membrane forms around each set of chromosomes to create two new nuclei.Then single cell pinches in the middle to form two separate daughter cells in which each contain a full set of chromosomes within a nucleus. This process is known to be cytokinesis. Meiosis II 6.
Spindle fibers attach to the centromeres. In anaphase, the sister chromatids are pulled toward opposite poles. In telophase, the chromosomes condense, and a new nuclear envelope forms around the groups of chromosomes. The nucleoli and nuclear envelope reappear and in cytokinesis, the cytoplasm divides into two cells, which are both diploid and genetically identical. 2.
The next stage is metaphase 2 the chromosomes line up along the center of the cell before it breaks up into two. Then the chromatids point towards the opposite ends of the cell. The next stage is anaphase 2. This is the second to last phase in meiosis and it has many events that happen. The first event is when the sister chromatids separate and move towards the opposite ends of the pole.
Then, in the Anaphase, centromeres divides and the each chromatid moves apart. Finally, daughter chromosomes approaching poles and loss individuality. Nucleolus reappears and nuclear membrane reconstituted. (picture source: http://cyberbridge.mcb.harvard.edu/mitosis_3.html) There are some specific checkpoint which is the regulation mechanism of the cell cycle. When certain conditions are met, the cell cycle will continue, so the cell ... ... middle of paper ... ...finally inversions is change the nucleotide sequence.
Metaphase ends when all the chromatids are aligned in the plane of the metaphase plate. Anaphase The centromere of each chromatid pairs splits and the chromatids separate. The daughter chromosomes are pulled toward opposite ends of the cell along the chromosomal microtubules. Anaphase ends when the daughter chromosomes arrive near the centrioles at opposite ends of the cell. Telophase During telophase, each cell prepares to return to the interphase state.