Translocation Down Syndrome

Translocation Down Syndrome - (after fertilization). Mosaic...

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Translocation Down Syndrome A translocation is the movement of a chromosomal segment from one chromosome to another nonhomologous chromosome. Five percent of Down Syndrome cases involve a translocation. The translocation often involves chromosome 14. In the translocation diagrammed below, chromosome #21 has become fused with chromosome #14. During meiosis, the two chromosomes might align so that each daughter cell receives one chromosome 21 as shown below. This will produce a normal egg. If the chromosomes align as illustrated below, one daughter cell will receive two chromosome 21s and the other will not receive any. When a gamete with two 21s fuses with a normal gamete, the result is a zygote with three chromosome 21s.
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This form runs in families and is not age-related. Mosaic Down Syndrome Some of the cells of mosaic Down's sydrome are trisomy 21 but others are normal. This is due to nondisjunction that occurs during mitosis
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Unformatted text preview: (after fertilization). Mosaic Down Syndrome is likely to be less severe because some of the cells are normal. Trisomy 18 (Edward Syndrome) The incidence of Trisomy 18 is approximately 1 out of every 3000 live births. Trisomy 18 is associated with mental and physical retardation, skull and facial abnormalities, defects in all organ systems, and poor muscle tone. Mean survival is 2 to 4 months. Less than 10% survive to 1 year; a few survive to their 20s or 30s. Trisomy 13 (Patau Syndrome) The incidence of Trisomy 13 is is approximately 1 out of 16,000 live births. Trisomy 13 produces mental and physical retardation, skull and facial abnormalities, and defects in all organ systems. It is also associated with a left lip, a large, triangular nose, and extra digits. Eighty percent die in the first month, five to ten percent live past the first year....
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Translocation Down Syndrome - (after fertilization). Mosaic...

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