Genetics - A. V. Sivolob 2008

Variability of Genetic Material

One of the universal properties of biological systems is their conservatism—The ability to restore genetic material and transmit it to offspring in a nearly unchanged form. The molecular machinery of DNA Replication and Repair (Chapter 1) ensures an exceptionally high fidelity of Genetic information maintenance, with an error rate of ~10^-10 nucleotide substitutions, meaning less than one substitution per eukaryotic genome per METABOLISM/36.html">DNA replication cycle. Naturally, absolute fidelity in DNA replication is impossible, and Variability of the genetic material is also a vital aspect of its existence.

Variability can be defined as the capacity of the genetic apparatus for changes that cause phenotypic differences among individuals of the same species across generations or within a single generation. Variability may be driven by Changes in the genome (hereditary variability) or arise from alterations in Gene Expression due to environmental factors during individual development (non-hereditary variability).

Hereditary variability may result either from the generation of novel DNA nucleotide sequence variants (mutational variability) or from new combinations of pre-existing sequences generated through recombination and the random assortment of Chromosomes during Meiosis. The mechanisms and consequences of recombinational variability are discussed in Chapters 1 and 3, whereas this chapter focuses specifically on mutational variability. A distinction should also be made between true mutational variability, which leads to random alterations in genetic programs (the focus of the Structure/133.html">Discussion below), and programmed changes of the genetic material in specific genomic regions or occasionally on a whole-genome scale, Examples of which will be examined in Chapters 5 and 6.

Mutations are unprogrammed, random, and stable (permanent and heritable) Changes in DNA structure that arise either from the action of damaging agents or As a result of errors in replication, repair, or recombination systems. A mutation occurring in somatic Cells (somatic mutation) is inherited only across Cell lineages, whereas one occurring in Germ Cells (germline mutation) is transmitted to subsequent generations of offspring. In addition to mutations arising in the nuclear genome (nuclear mutations), alterations can also occur in Mitochondrial and Chloroplast DNA—these are known as cytoplasmic mutations.