DELETION (GENETICS)

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.

Contents

Causes

Types

Effects

See also

Reference

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'.

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.
Deletions are responsible for an array of genetic disorders, including some cases of male infertility and two thirds of cases of Duchenne muscular dystrophy. A deletion of part of the short arm of chromosome 5 results in a syndrome called Cri du chat, 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.

See also

★ Chromosome abnormalities

★ Null allele

Reference

1. Lewis R. 2005. ''Human Genetics: Concepts and Applications'', 6th Ed. McGraw Hill, New York.