Genetic

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 imbalance is to describe situation when the genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

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

Rearrangement

Rearrangement may refer to:* Rearrangement reaction* Rearrangement inequality...

s or aneuploidy

Aneuploidy

Aneuploidy is an abnormal number of chromosomes, and is a type of chromosome abnormality. An extra or missing chromosome is a common cause of genetic disorders . Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy occurs during cell division when the chromosomes do not separate...

.
Changes in gene dosage

Gene dosage

Gene dosage is the number of copies of a gene present in a cell or nucleus. An increase in gene dosage can cause higher levels of gene product if the gene is not subject to regulation from elsewhere in the body....

, the number of times a given gene is present in the cell nucleus

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

, can create a genetic imbalance.

Effect

This imbalance in gene dosage alters the amount of a particular protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

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

Survival is the struggle to remain alive and living. The term may refer to:- Companies and organisations :* Survival International, a non-governmental human rights organization working for tribal peoples- Literature :...

 of the organism.

Mostly not harmful

Diminishing the dosage of most genes produces no obvious change in phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

.

Some Are Noticeable

The phenotypic consequences of a decrease in gene dosage for certain genes are noticeable but not catastrophic. For example, Drosophila containing only one copy of the wild type

Wild type

Wild type refers to 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, "mutant" allele...

 Nocth gene have visible wing abnormalities but otherwise seem to function normally.

Rare Are Lethal

For some rare genes, the normal diploid level of gene expression

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

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

Lethality

Lethality is a term designating the ability of a weapon to kill. Most often this term is used when referring to chemical weapons, biological weapons, or their chemical components. The use of this term denotes the ability of these weapons to kill, but also the possibility that they may not kill...

. In Drosophila

Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

, a single dose of the locus known as Triplolethal is in an otherwise diploid individual.

Be Lethal In Other Situations

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

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

.