Genetics with Basics of Selection - M.P. Myhun - 2008

CHAPTER II. Physical Basis and Molecular Mechanisms of Heredity

2.6. General Features of Genome Organization and Function

A genome is the haploid set of Chromosomes containing a complete single set of genes.

For haploid Cells and organisms, The concepts of The Genome and the genotype are identical.

Often, the entire genome consists of just a single nucleic acid molecule—either DNA or RNA. This is characteristic of most Viruses and Bacteria.

The length of the nucleic acid molecule ranges from 0.4 to 1 µm (10^-3 mm) in the smallest viruses, to 5–100 µm in Plastids and Cell/35.html">Mitochondria, and 1,000–2,000 µm in bacteria.

In eukaryotes, the length of a nuclear DNA molecule can be measured in centimeters (averaging 5 cm in humans). Genome Size is also measured by the number of NUCLEOTIDES or nucleotide pairs (bp) in the case of double-stranded molecules. A double-stranded DNA fragment containing 1,000 bp is designated as one kilobase (kb).

The nucleic acid comprising the genome, with its specific nucleotide sequence, encodes the set of Proteins necessary for life processes.

A DNA molecule may contain so-called non-coding sequences that do not contain genes. These sequences include various structural regulatory regions of DNA, as well as relatively monotonous nucleotide sequences whose Functions are not yet fully understood.

The presence of non-coding sequences and repeats in DNA accounts for what is known as genome redundancy. The Essence of this phenomenon is that the length of genomic DNA molecules is significantly greater than what is required to encode the necessary number of proteins.

Viral genomes consist of one or more molecules of genetic nucleic acid, with each such molecule enclosed in a protein coat called a capsid.

The bacterial genome consists of a circular double-stranded chromosomal DNA molecule and numerous extrachromosomal circular DNA molecules known as Plasmids.

An important feature of Eukaryotic Genomes is the presence of repeats and multiplications (multiple repeats) of individual sequences, alongside numerous short and long non-coding sequences located both between genes and within genes. All of this contributes to the pronounced redundancy of Introduction/5.html">Eukaryotic Cell genomes.

It should be noted that traditional views On the Stability of Genetic information in living nature were challenged in the 1970s by the discovery of mobile (transposable) genetic elements (MGEs) in bacteria. Today, a vast variety of MGEs capable of moving within the genomes of both bacteria and eukaryotes are known.