Chromosomes
are made of tightly wound DNA and protein.
Genes are found along the length of chromosomes.
A gene is a segment of DNA that contains
instructions for making a specific protein
or proteins required by the body. Human
beings have about 30,000 - 35,000 genes.
We have two copies of each gene, but the
copies can be slightly different. For
example, the gene associated with cystic
fibrosis has more than 1000 different
variations. Different versions of the
same gene are called its alleles, and
everyone has two alleles for each gene.
(Males have only one X chromosome, so
they only have one copy of the genes located
on the X chromosome.)
Image courtesy
of the U.S. Department of Energy Human
Genome Program, http://www.ornl.gov/hgmis.
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