Chromosomal information on cri du chat
Cri-du-chat is caused by a deletion on the short arm of the fifth chromosome. Multiple genes are missing as a result of this deletion, and each may contribute to the symptoms of the disorder. One of the deleted genes known to be involved is TERT (telomerase reverse transcriptase). This gene is important during cell division because it helps to keep the tips of chromosomes (telomeres) in tact.
A deletion is caused by a break in the DNA molecule that makes up a chromosome. In most cases, the chromosome break occurs while the sperm or egg cell (the male or female gamete) is developing. When this gamete is fertilized, the child will develop cri-du-chat syndrome. The parent, however, does not have the break in any other cells of the body and does not have the syndrome. In fact, the break is usually such a rare event that it is very unlikely to happen again if the parent has another child.
When deletions occur during the formation of an egg or sperm, it is caused by unequal recombination during meiosis. Recombination normally occurs between pairs of chromosomes during meiosis while they are lined up at the metaphase plate. If the pairs of chromosomes don't line up correctly, or if the chromosome breaks aren't repaired properly, the structure of the chromosome can be altered.
(See: Graphics for illustrations of this break).
A deletion is caused by a break in the DNA molecule that makes up a chromosome. In most cases, the chromosome break occurs while the sperm or egg cell (the male or female gamete) is developing. When this gamete is fertilized, the child will develop cri-du-chat syndrome. The parent, however, does not have the break in any other cells of the body and does not have the syndrome. In fact, the break is usually such a rare event that it is very unlikely to happen again if the parent has another child.
When deletions occur during the formation of an egg or sperm, it is caused by unequal recombination during meiosis. Recombination normally occurs between pairs of chromosomes during meiosis while they are lined up at the metaphase plate. If the pairs of chromosomes don't line up correctly, or if the chromosome breaks aren't repaired properly, the structure of the chromosome can be altered.
(See: Graphics for illustrations of this break).