Deletion on a chromosome

In genetics, a deletion (also called gene deletion, deficiency, or deletion mutation) is a mutation (a genetic aberration) in which a part of a chromosome or a sequence of DNA is missing. Deletion is the loss of genetic material. Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome.^[1] Deletions can be caused by errors in chromosomal crossover during meiosis. This causes several serious genetic diseases. For a non-technical introduction to the topic, please see Introduction to genetics. ... It has been suggested that mutant be merged into this article or section. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... Articles with similar titles include miosis. ... A genetic disorder, or genetic disease is a disease caused, at least in part, by the genes of the person with the disease. ...

Causes

Causes include the following:

• Losses from translocation
• Chromosomal crossovers within a chromosomal inversion
• Unequal crossing over
• Breaking without rejoining

For synapsis to occur between a chromosome with a large intercalary deficiency and a normal complete homolog, the unpaired region of the normal homolog must loop out of the linear structure into a deletion or compensation loop. Chromosomal translocation of the 4th and 20th chromosome. ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. ... It has been suggested that this article or section be merged into meiosis. ...

Types

Types of deletion include the following:

• Terminal Deletion - a deletion that occurs towards the end of a chromosome.
• Intercalary Deletion - a deletion that occurs from the interior of a chromosome.

Effects

Small deletions are less likely to be fatal; large deletions are usually fatal - but always, there is variation based on what genes are lost. Some medium-sized deletions lead to recognizable human disorders.

Deletion of a number of base pairs that is not evenly divisible by three will lead to a frameshift mutation, causing all of the codons occurring after the deletion to be read incorrectly during translation, producing a severely altered and potentially nonfunctional protein. Framing error is the following: Generally, a framing error is the result of reading a string of symbols which are grouped in blocks starting at the wrong point. ... RNA codons. ... Translation is the second process of protein biosynthesis (part of the overall process of gene expression). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

Deletions are responsible for an array of genetic disorders, including some cases of male infertility and two thirds of cases of Duchenne muscular dystrophy.^[1] A deletion of part of the short arm of chromosome 5 results in a syndrome called Cri du chat,^[1] also known as "cry of the cat" syndrome. It is found in approximately 1 in 50,000 live births. The surviving infants have a distinctive cry, severe mental retardation, and shortened life span. Infertility is the inability to naturally conceive a child or to carry a pregnancy to full term. ... Muscular Dystrophy is a genetic condition that describes over 20 genetic and hereditary muscle diseases. ... Cri du chat syndrome (French for Cry or call of the cat), also called deletion 5p syndrome, or 5p minus, is a rare genetic disorder due to a missing portion of chromosome 5. ...

See also

• Chromosome abnormalities
• Null allele

A chromosome abnormality reflects an abnormality of chromosome number or structure. ... A null allele is an allele with the effect of either absence of the gene product at the molecular level, or the absence of function at the phenotypic level. ...

Reference

1. ^ ^{a b c} Lewis R. 2005. Human Genetics: Concepts and Applications, 6th Ed. McGraw Hill, New York.