Cytokinesis in Animal Cells
Cytokinesis is the actual process of cell division, where the cell either stretches apart until it becomes two separate cells (animal cells) or it. This animal cell has also made a copy of its centrosome, an organelle that will play a key role in orchestrating mitosis, so there are two centrosomes. (Plant cells . Comparison of Mitosis and Meiosis | Gametogenesis | Links Human beings ( except for their gametes), most animals and many plants are diploid.
Ploidy is a term referring to the number of sets of chromosomes.
Cytokinesis in Animals: Mitosis, Meiosis and More
Organisms with more than two sets of chromosomes are termed polyploid. Chromosomes that carry the same genes are termed homologous chromosomes. The alleles on homologous chromosomes may differ, as in the case of heterozygous individuals. Organisms normally receive one set of homologous chromosomes from each parent.
Meiosis is a special type of nuclear division which segregates one copy of each homologous chromosome into each new "gamete". Mitosis maintains the cell's original ploidy level for example, one diploid 2n cell producing two diploid 2n cells; one haploid n cell producing two haploid n cells; etc.
Meiosis, on the other hand, reduces the number of sets of chromosomes by half, so that when gametic recombination fertilization occurs the ploidy of the parents will be reestablished. Most cells in the human body are produced by mitosis. These are the somatic or vegetative line cells.
Cells that become gametes are referred to as germ line cells. The vast majority of cell divisions in the human body are mitotic, with meiosis being restricted to the gonads.
Life Cycles Back to Top Life cycles are a diagrammatic representation of the events in the organism's development and reproduction. When interpreting life cycles, pay close attention to the ploidy level of particular parts of the cycle and where in the life cycle meiosis occurs.
Phases of mitosis
For example, animal life cycles have a dominant diploid phase, with the gametic haploid phase being a relative few cells.
Some textbooks list five, breaking prophase into an early phase called prophase and a late phase called prometaphase.
These phases occur in strict sequential order, and cytokinesis - the process of dividing the cell contents to make two new cells - starts in anaphase or telophase. You can remember the order of the phases with the famous mnemonic: The cell has two centrosomes, each with two centrioles, and the DNA has been copied.
CELL DIVISION: Meiosis
At this stage, the DNA is surrounded by an intact nuclear membrane, and the nucleolus is present in the nucleus. This animal cell has also made a copy of its centrosome, an organelle that will play a key role in orchestrating mitosis, so there are two centrosomes. The mitotic spindle starts to form, the chromosomes start to condense, and the nucleolus disappears. In early prophase, the cell starts to break down some structures and build others up, setting the stage for division of the chromosomes.
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The chromosomes start to condense making them easier to pull apart later on. The mitotic spindle begins to form.
The spindle grows between the centrosomes as they move apart. The nucleolus or nucleoli, plurala part of the nucleus where ribosomes are made, disappears.
This is a sign that the nucleus is getting ready to break down. The nuclear envelope breaks down and the chromosomes are fully condensed. In late prophase sometimes also called prometaphasethe mitotic spindle begins to capture and organize the chromosomes. The chromosomes finish condensing, so they are very compact.Cell Cycle & Cell Division - Comparison of Mitosis in Plants and Animals
The nuclear envelope breaks down, releasing the chromosomes. Anatomy of the mitotic spindle. Diagram indicating kinetochore microtubules bound to kinetochores and the aster.
The aster is an array of microtubules that radiates out from the centrosome towards the cell edge. Diagram also indicates the centromere region of a chromosome, the narrow "waist" where the two sister chromatids are most tightly connected, and the kinetochore, a pad of proteins found at the centromere. Microtubules can bind to chromosomes at the kinetochore, a patch of protein found on the centromere of each sister chromatid.
Centromeres are the regions of DNA where the sister chromatids are most tightly connected. Microtubules that bind a chromosome are called kinetochore microtubules.
Following prophase is metaphase, in which the chromatid turned chromosomes line up across the center of the cell forming a metaphase plate. Next is anaphase, in which the spindles of the cell pull the chromatids apart to the ends of the cell.
This allows the daughter and parent cells to have an equal amount of genetic material. The last stage is telophase, and this is where cytokinesis in animals takes place.
When an animal cell begins to divide, it is attributed to a structure called a contractile ring. Meiosis and Cytokinesis in Animal Cells Similar to mitosis, meiosis is the division of sexual gametes such as the sperm and ova cells. The stages of meiosis are similar to mitosis in that it has prophase, metaphase, anaphase, and telophase.