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    Genetics Terminology: 
    Chromosomes & Sister Chromatids

    CLASS NOTES from Science Prof Online


    Nuclear and Cellular Division
    During nuclear division, the chromosomes line up at the cell's equator and then the sister chromatids separate and move to opposite ends of the cell (poles). Once separated these former sister chromatids are now each considered a chromosome. 
    Article Summary: When is DNA considered a chromosome? What is a sister chromatid and how does it differ from a chromosome? This article unravels some of the lingo of DNA.
    Duplicated Chromosomes vs. Sister Chromatids
    Two joined sister chromatids:
    1) Chromatid, (2) Centromere,
    (3) Short arm, (4) Long arm
    Preparing for Nuclear Division
    For most of the cell cycle, the DNA molecules are in very long strands called chromatin. But when the cell prepares to divide, it must pack its DNA for the move. So prior to cell division, the chromatin condenses. This replicated DNA molecule, in its condensed form, is now referred to as a chromosome
    Students often become confused when it comes to the genetics terminology associated with chromosomes and chromosome number. What are 
    Sources & Resources
    • , Genetic Science Learning Center, University of Utah.
    • Genetics Terminology:  animation from John Kyrk.
    • , animation & quiz from McGraw-Hill.
    • , animation & quiz from McGraw-Hill.
    •  animation & quiz from McGraw-Hill.
    • Cell Division: 
    Page last updated: 10/2015
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    Dominant Genetic Trait of Tongue Rolling
    What are chromatids? How do all of these terms differ and how do they relate to each other? To understand these terms, we must first review cell division. 

    Cells Divide to Make More Cells
    During the cell cycle, somatic cells (non reproductive cells) of 
    DNA molecule replicating: Strands separating so that the DNA can be read and replication can occur.
    But, remember, there are two copies attached to each other until nuclear division. Each of the two copies of a chromosome are designated as a sister chromatid and they are physically linked together at a point on the chromosome called the centromere.

    Once the chromosomes move to opposite poles, the dividing cell reforms a nuclear membrane around each of the two areas of separated genetic material. The cell itself then proceeds to divide in a process called cytokinesis, and what was once one cell becomes two, completing the process of mitosis.