305. Identifying Satellite Sequences (EXP-305)
Satellite DNA DNA from calf thymus (even numbered lanes) was digested with EcoR1 prior to this electrophoretic separation. Note the discrete satellite DNA band.
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A large fraction of the DNA of vertebrates consists of nucleotide sequences that are repeated thousands or more times in the genome. Satellite sequences are a major class of these repeated elements and these sequences are found in most eukaryotic organisms. There are about 1 million cutting sites for the restriction enzyme EcoRI in the typical vertebrate genome and about 1 million DNA fragments are generated following digestion of vertebrate DNA with this enzyme. When this DNA is separated by electrophoresis, the large number of differently-sized fragments appear as a background smear on the gel lane. However, as shown in the figure below, DNA fragments from the highly repeated satellites form discrete bands because they are the same size. In this exercise, students identify satellite sequences in the cow genome and determine if such sequences are present in chicken DNA.