Chromosomal Deletion

Chromosomal Deletion

Loss of a chromosome segment is known as deletion or deficiency. When the missing segment contains a telomere of the affected chromosome, it is called terminal deletion; such deletions are believed to be uncommon. In most deficiencies, however, the missing segment does not contain a telomere; such deletions are known as interstitial or intercalary deletions. In 1938, Muller postulated that the loss of telomere makes a chromosome end unstable so that it tends to unite with a similar damaged end. According to this view, all deficiencies that can be maintained in populations must be necessarily intercalary. This view is supported by considerable data reviewed by Roberts (1975) who believes that all supposedly terminal deletion are capped by very small telomeres, and, therefore, are intercalary. Thus the occurrence of really terminal deficiencies is doubtful; but some deletions in Drosophila may be terminal
DELETION IN MAN
Deletions have been described in human beings; each deletion appears to produce a distinct set of symptoms or ‘syndromes’. The group of symptoms that characterizes an abnormality or a disease is known as syndrome. A specific deletion in chromosome 22 produces a chromosome called ‘Philadelphia 22’; this chromosome is associated with chronic myelogenous leukaemia. Another deficiency in chromosome 5 produces ‘cri-du-chat’ syndrome. Individual’s sufferings from this syndrome produce a characteristic mewing catlike cry during childhood; have unique facial features and exhibit severe physical and mental retardation.