Genetic imbalance is to describe situation when the

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

of a cell or organism has more copies of some genes than other genes due to

chromosomal A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most importa ...

rearrangements or

aneuploidy Aneuploidy is the presence of an abnormal number of chromosomes in a cell (biology), cell, for example a human somatic (biology), somatic cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more plo ...

. Changes in gene dosage, the number of times a given gene is present in the

cell nucleus The cell nucleus (; : nuclei) is a membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have #Anucleated_cells, ...

, can create a genetic imbalance.

Effects

This imbalance in gene dosage alters the amount of a particular

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

relative to all other proteins, and this alternation in the relative amounts of protein can have a variety of

phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

effects. These effects are depending on how the proteins function and how critical the maintenance of a precise ratio of proteins is to the

survival Survival or survivorship, the act of surviving, is the propensity of something to continue existing, particularly when this is done despite conditions that might kill or destroy it. The concept can be applied to humans and other living things ...

of the organism. Diminishing the dosage of most genes produces no obvious change in

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

. For some genes the phenotypic consequences of a decrease in gene dosage are noticeable but not catastrophic. For example, ''Drosophila'' containing only one copy of the

wild type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...

Notch gene has visible wing abnormalities but otherwise seems to function normally. For some rare genes, the normal

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

level of

gene expression Gene expression is the process (including its Regulation of gene expression, regulation) by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, ...

is essential to individual survival; fewer than two copies of such a gene results in

lethality Lethality (also called deadliness or perniciousness) is how capable something is of causing death. Most often it is used when referring to diseases, chemical weapons, biological weapons, or their toxic chemical components. The use of this term ...

. In

Drosophila ''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...

, a single dose of the locus known as Triplolethal is in an otherwise diploid individual. Although a single dose of any gene may not cause substantial harm to the individual, the genetic imbalance resulting from a single dose of many genes at the same time can be lethal. Humans, for example, cannot survive, even as

heterozygotes Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mos ...

, with deletions that remove more than about 3% of any part of their

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

References

* {{refend Genetics