False
Explanation:
We call the whole genome of the DNA of a cell of a species and the genes it contains. Strictly speaking, the human genome not only comprises the DNA of the nucleus but also that of the mitochondria that, although only 16,000 bases in length, is essential for cellular functioning. Genes are segments of DNA capable of being transcribed - that is, copied - to an RNA molecule (ribonucleic acid) with the same sequence as the gene. The genes are not juxtaposed along the chromosomes, but rather scattered and separated at great distances by intergenic DNA sequences. Intergenic regions constitute 70% of the genome, while genes represent only 30%. It is estimated that the human genome has about 20,000 genes. These genes encode different types of RNA, among which are the so-called messenger RNAs, which in turn encode proteins. The other RNAs, those that are not messengers, receive the generic name of non-coding RNAs: they are not intermediaries between the gene and the protein but rather they fulfill functions in themselves. Among these are ribosomal, transfer, small nuclear RNAs, micro RNAs and ribozymes. Therefore, the definition according to which a gene is the segment of DNA that encodes a protein is not strictly correct: many genes encode proteins, but not all. Each of the genes that encode proteins has regions that will be represented in mature messenger RNA interspersed by others whose sequences will not be represented there. The first regions are called exons, while the second are introns. While introns are not coding, most exons are regions of the genome that encode proteins. These regions constitute only 1.5% of the genome.
