Human chromosomes during cell division. Karyotype of a human cell.
The term karyotype refers to the basic map, or picture, of the number,type, and structure of the chromosomes of a cell. The karyotype is created through a process in which a cell’s mitotic division is halted or trapped during metaphase and held suspended by chemicals. As a result, chromosomes in the cell’s nucleus become untangled and separate themselves from other chromosomes. Later, the cell is stained and viewed under a microscope. Once the various chromosomes are revealed, scientists may then create a chromosome map. All eucaryotic cells possess chromosomes and therefore possess a specific karyotype. A normal human karyotype, for example, includes 46 chromosomes or 23 pairs of chromosomes. Of these 46 chromosomes, both the male and the female each possess 22 pairs of autosomes, or non-sex chromosomes, and one pair of sex chromosomes. For the male, the sex chromosomes are XY. For the female, the sex chromosomes are XX.
Human chromosomes during cell division. Karyotype of a human cell.
The karyotype holds great importance because it enables scientists to view the layout of chromosomes in a particular plant or animal. By mapping out specific chromosome pairs, a scientist can readily identify the sex of a particular animal or plant. Also, a scientist is able to detect certain abnormalities that may exist due to a cell’s having an extra chromosome, lacking a chromosome, or having a chromosome that is not fully developed. In humans, chromosomal defects can result in a variety of disorders, including mental retardation and diseases.
As indicated above, through the use of the karyotype modern science is able to identify the sex of a particular organism. For humans, this information can be invaluable, as illustrated in the idea that parents are able to gain insight into the miracle of life which they have created-- the fertilization of a female’s egg cell by a male’s sperm cell-- and the sex of their resulting offspring (male or female), which this process produces. More important than identifying the sex of a child, is the idea that scientists are able to identify abnormalities and chromosomal defects via the karyotype. A profound debate is that of whether or not scientists have the right to “play God”. Due to the fact that scientists have the technology to alter abnormal chromosomes, the problem arises over the question of what, if anything, scientists should have the power to change-- i.e. the genetic makeup of a particular organism. This was attempted during W.W.II in Germany and its consequences resulted in racist ideology and ultimately, in genocide. Still, the possibility for the eradication of various genetic diseases is a powerful concept and serves as a driving force behind genetic research. The debate will persist until scientists and religious groups in society agree on ethical and moral strategies for research.
The chromosomes of most eukaryotes vary greatly in size and shape. For each chromosome of varying size and shape, there exists a chromosome to match it. Therefore, a chromosome pair is simply the pair of homologous (resembling in structure and origin) chromosomes, one derived from the maternal, one derived from the paternal parent, which become associated at meiosis. These chromosome pairs can be seen in the karyotype, where they are usually assigned a particular number (one through twenty-two) for non-sex chromosomes, or a particular letter (X or Y) for the sex chromosomes, respectively.
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Primer on Molecular Genetics
is a basic introduction and overview of molecular genetics. It covers areas such as DNA, genes, and chromosomes and provides understandable definitions. It goes on to provide images which illustrate the above terminology.Human Genome Project is a more in-depth and detailed web site which covers genetics; and more specifically, it provides a link to a web site with information about the HGP-- Human Genome Project. This site provides a plethora of information on genetics and genetics related topics.