Genetic content and repeated sequences in the genome

The genome is the total set of genes present in the cell. Research has shown that:

• In prokaryotes, most of the DNA molecule represents codes for building proteins and enzymes.
• In eukaryotes, less than 70% of the DNA represents codes for building RNA and protein, while more than 30% represents parts that do not code.

Repeated sequences

• Repeated sequences occur in the genome: for example the base sequence AGACT repeats 100,000 times in the middle of one chromosome of the fruit fly Drosophila, and it does not represent a code.
• Some genes repeat hundreds of times to build enormous quantities of protein and RNA, as in the genes that build histones and rRNA.

Telomeres

Telomeres are structures at the ends of chromosomes that do not code; their function is to preserve the structural integrity of the chromosome and prevent its erosion.