Sex%20Chrom%20Abn

Sex%20Chrom%20Abn - Sex Chrom Abn 04/20/03 6:53 PM SEX...

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SEX CHROMOSOME ABNORMALITIES Sometimes during meiosis, the paired (M I ) or daughter chromosomes (M II ) go to the same pole. This is described as " nondisjunction ". If nondisjunction involves the sex chromosomes, it results in eggs or sperm with abnormal numbers of X and/or Y chromosomes. In eggs, a single nondisjunction event leads to XX eggs and O (no X chromosome) eggs. Fertilization of an XX egg with an X sperm produces XXX (Triplo X) females Fertilization of an XX egg with a Y sperm produces XXY (Klinefelters) males. Fertilization of an O egg with an X sperm leads to XO (Turners) females Fertilization of an O egg with a Y sperm is lethal Nondisjunction in males can lead to XX, XY, O and YY sperm. Combining these with an X egg will produce the syndromes described above plus XYY (Jacobs) . Females with the karyotype 47; XXX are fertile, tend to have XX and XY offspring, generally fall in the normal range of IQ, and have no distinguishing characteristics. Many are considered "shy" when young and may be delayed in social development. There is great tendency for metal retardation when there are 4, 5, or 6-X chromosomes present. Overall frequency: about 1 in 4,000 live births. Females with Turners syndrome (45; XO) are very short, sterile, and have problems with "spatial" tests but otherwise tend to fall in the normal IQ range. Development of secondary sex characteristics and stature can be addressed by hormone therapy. Heart and kidney problems are also common. Frequency: 1 in 2,000 to 1 in 2,500 live female births
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This note was uploaded on 04/29/2008 for the course GENE 310 taught by Professor Magill during the Spring '08 term at Texas A&M.

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Sex%20Chrom%20Abn - Sex Chrom Abn 04/20/03 6:53 PM SEX...

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