(a)+Chromosomes

=**Chromosomes:**=

**1. Definition:**
Chromosomes are organized structures of genetic information found in the nucleus of cells (Hodgkinson). Also, Chromosomes contain DNA-bound proteins, which serve to package the DNA and control its functions.

**2. Structure:**
They are made up of genes, which are short sections of DNA (our genetic material) carrying the instructions for one feature. So chromosomes are made up of genes, which are made up of DNA (Hodgkinson). This is explained in the diagram bellow:

Our genetic material is also extremely long. Because of this, they are coiled into a tightly packed structure in order to fit into cells. How this is done is shown in the video bellow: media type="youtube" key="gbSIBhFwQ4s" height="315" width="560"(How DNA)

=**Karyotype:**=

**1. Definition:**
A karyotype is a visual representation of one's chromosomes as seen through a microscope (Karyotype Definition). Bellow is an example of a human karyotype. (A Human)

**2. How they are found:**
Karyotype testing is performed in different ways depending on the source you are retrieving information from and the goal of performing the karyotype. For newborns multiple blood samples are retrieved; white blood cells, red blood cells, serum, and many other fluids. Although all of these samples are needed in the test, the test is performed on the white blood cells. For karyotype performed during a pregnancy samples come from the amniotic fluid. These samples are used because the cells need to be divided and white blood cells and fetal cells (from the amniotic fluid) are always dividing. The scientists performing this test have to wait up to a week to have enough cells to actually be able to perform the test. Once they have enough cells, they than use chemicals to have all of the cells synchronize their stages of mitosis. Because metaphase is the phase in which chromosomes are easiest seen in due to their compact form, the scientists wait until the mitosis process has reached this stage, then using a chemical they stop the process of mitosis.. Next the chromosomes must be ejected from the cell allowing the chromosomes to be seen. This is done by using a solution that causes the cell to burst. This is done on a microscope slide allowing for the chromosomes to not be lost. Becuase chromosomes are naturally colorless, a dye is then used to stain the chromosomes. Next, the chromosomes are placed under the microscope and are counted by the scientist. Then they are sorted by the length of the chromosome. Finally, the scientist is able to see all of the chromosomes and observe all of the abnormalities that may be present. (Fergus)

**3. Their Use:**
Karyotypes are able show the characteristics of chromosomes, therefore it can be analyzed to see if any chromosomal abnormalities are present. Because of this humans can use it to help diagnose for birth defects, cancers, or genetic disorders (O'Connor). There are several characteristics that are looked at in karyotypes to determine this:
 * 1) The absolute size of the chromosome
 * 2) The position of the chromosomes centromere (usually found at the center of chromosomes)
 * 3) The relative size of the chromosome
 * 4) The number of chromosomes
 * 5) Number and position of sattelites (small parts which are attached to the chromosome with a thin thread)
 * 6) The degree and distribution of the heterochromatin (tightly packed DNA) in the chromosome.

For example one birth defect that is tested for using Karyotype testing is Down Syndrome. A karyotype test that identifies down syndrome would look like this

** Work Cited: **
Hodgkinson, Wayne. //Genetics//. Word Document. //How DNA Is Packaged (Advanced) //. //YouTube//. DNALearningCenter, 22 Mar. 2010. Web. 7 Feb. 2012. . A Human Karyotype. Digital image. //Biotechnology Online//. Murdoch Children's Medical Research Insitute. Web. 7 Feb. 2012. . Fergus, Kathleen. //How To : How is a Karyotype Test Done?// About, 2012. Web. 6 Feb. 2012. . "Karyotype Definition." //Beltina//. Web. 7 Feb. 2012. . "Karyotype Down Syndrome." //Book Bing//. N.p., n.d. Web. 9 Feb. 2012. . "Karyotype." //Wikipedia, the Free Encyclopedia//. 1 Feb. 2012. Web. 7 Feb. 2012. . O'Connor, Clare. "Karyotyping for Chromosomal Abnormalities." //Scitable//. 2008. Web. 7 Feb. 2012. . <span style="color: #000000; font-family: "Times New Roman","serif"; font-size: 15.99px;">"What Is a Karyotype?" //Inoveateus//. Web. 16 Feb. 2012. <http://www.innovateus.net/health/what-karyotype#What+are+the+Observations+on+karyotypes%3F>.