Chromosomes in Cells

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Chromosomes are the structures that hold our genes. Genes provide the information that tell our bodies how to develop, grow and function properly. Almost every cell in our body contains thousands of genes that are located on 46 chromosomes. These 46 chromosomes are arranged in 23 pairs. One member of each pair comes from our mother in the egg, and the other member comes from our father in the sperm. The first 22 pairs (called autosomes) are numbered according to size; the largest chromosome is chromosome 1, and the smallest chromosome is chromosome 22. The 23rd pair are the sex chromosomes labeled X and Y. Females have two X chromosomes and males have an X and Y chromosome.

The image to the right shows a kartyotype, or a photograph of chromosomes in a single cell. This particular image shows a normal male because it has 22 pairs of autosomes, and then the final pair of sex chromosomes shows XY. A normal female karyotype would also have 22 pairs of autosomes, but the sex chromosomes would show XX. A karyotype can be obtained by extracting chromosomes from a white blood cell in a blood sample. These chromosomes are then stained and viewed under a microscrope. A trained professional can identify and arrange these chromosomes according to length and banding pattern. A picture of the karyotype is then printed.

Although almost everyone has a complete set of chromosomes, sometimes pieces of chromosomes can be switched or moved. In general, as long as all of the material is present, the majority of people with rearranged chromosomes do not develop any health problems. However, when sections of or entire chromosomes are missing or duplicated, miscarriage, infant death, or disease usually occurs. For example, an extra copy of chromosome 21 results in Down Syndrome (trisomy 21).

[edit] References

Chromosome Deletion Outreach, Inc. 1996-2007. Introduction to Chromosomes. http://www.chromodisorder.org/CDO/General/IntroToChromosomes.aspx

Genetic Alliance. 2007. Understanding Genetics: A Guide for Patients and Health Care Professionals. http://www.geneticalliance.org/ws_display.asp?filter=understanding.genetics.download

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[edit] External Links

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