Deletion on a chromosome

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 - there are always variations based on which 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.^[1] 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. Deletion mutations are also responsible for the cat family's inability to taste sweetness.

See also

• Chromosome abnormalities
• Null allele

References

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