(excerpted from the GAPS Index http://aspin.asu.edu/geneinfo/abtchr.htm)
The human body is made up of billions of cells. At the centre of each cell is a special compartment called the nucleus which stores threads of DNA (Deoxyribonucleic Acid) arranged in chromosomes.6
A chromosome is a rod like structure present in the nucleus of all body cells, with the exception of the red blood cells, and which stores genetic information in the form of genes.6 The chromosomes are in their turn composed of 50,000 to 100,000 genes6 located on 46 chromosomes1 which contain the genetic blue print determining each individual’s characteristics.6
Simply put, chromosomes are the structures that hold our genes. Genes are the individual instructions that tell our bodies how to develop and keep our bodies running healthy.
These 46 chromosomes occur as 23 pairs. We get one of each pair from our mother in the egg, or ovum, and one of each pair from our father in the sperm.1
The ovum and sperm each carry 23 chromosomes and on fertilization the chromosomes combine to give a total of 23 pairs, 46 chromosomes in total. One pair of chromosomes determines the sex of the individual: males have an X and Y chromosome, while females have two X chromosomes.6
The first 22 pairs are labeled longest to shortest.1 Chromosome 1 is the longest pair and Chromosome 22 is the shortest pair.* The last pair are called the sex chromosomes labeled X or Y. Females have two X chromosomes (XX), and males have an X and a Y chromosome (XY).1
Human beings have cells with 46 chromosomes (2 sex chromosomes and 22 pairs of autosomal, that is, non-sex chromosomes). Males are 44,XY; females are 44,XX.6
Each chromosome is comprised of 2 extremely long DNA molecules in combination with chromosomal proteins. Genes are defined by intervals along one of the DNA molecules. The location of the is called the locus.4
Most genes carry information which is necessary to synthesize a protein. The pairs of autosomal chromosomes (one from mom and one from dad) carry basically the same information; that is, each has the same genes, but there may be slight variations in the DNA sequence of nucleotide bases in each gene. Alleles are different variants of a particular gene.4
Human chromosomes are composed of Nucleic Acid (DNA or RNA), Phosphate and Sugars. Double helix DNA acts as a skeleton of Human Chromosomes and help to store all the messages (codes) of basic cellular function. The combination of bases i.e., Adinine (A), Guanine (G), Thymine (T), and Cytosine © help to form words or genes which carry basic messages from nucleus to cytoplasm. Any alteration in basis can lead to genetic defects.4
The information contained in the nucleotide sequence of a gene is transcribed to mRNA (messenger RNA) by enzymes in the cell’s nucleus and then translated to a protein in the cytoplasm. This protein may be a structural constituent of a given tissue. It may be an enzyme which catalyzes a chemical reaction, or it may be a hormone. There are also many other potential functions for proteins.4
Sources of information:
* Editorial or supplementary comments from the editors at Genetic Information and Patient Services, Inc (GAPS)
1. Chromosome Deletion Outreach http://members.aol.com/cdousa/intro.htm
2. NetWellness.com http://netwellness.org/healthtopics/idbd
3. adam.com http://oso.adam.com/ency/article/002053.htm
4. adam.com http://oso.adam.com/ency/article/002048.htm
5. American Society of Human Genetics http://www.ferre.org/newbrow/genetic.html
6. CaF (Contact a Family) http://www.cafamily.org.uk/inherita.html
7. Virtual Hospital http://www.vh.org/Providers/Textbooks/
ClinicalGenetics/AppendixD/AppenDContents.html
8. http://www.mcoexecutives.com/genetic1.htm
9. March of Dimes http://www.noah.cuny.edu/pregnancy/march_of_dimes
/genetics/gcbooklt.html#About Genetics and Inherited Traits
10. http://www.indiaspace.com/pages/genetics.htm
11. USD http://med.usd.edu/som/genetics/curriculum/
1ECHROM3.htm
12. CMGS http://ich.ucl.ac.uk/cmgs/chromabs.htm
13. Palomar http://daphne.palomar.edu/abnormal/
diagnostic_tests.htm |
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Last Updated ( Sunday, 14 November 2004 )
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Genetic Info 
