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Ch. 5 - Sex Determination and Sex Chromosomes
Klug - Essentials of Genetics 10th Edition
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Tutti i libri di testoKlug 10th EditionCh. 5 - Sex Determination and Sex ChromosomesProblema 17
Capitolo 5, Problema 17

Indicate the expected number of Barr bodies in interphase cells of individuals with Klinefelter syndrome, Turner syndrome, and karyotypes 47, XYY, 47, XXX, and 48, XXXX.

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Recall that a Barr body is an inactivated X chromosome found in the nuclei of cells with more than one X chromosome. The number of Barr bodies is always one less than the total number of X chromosomes present in the cell.
For Klinefelter syndrome (typically 47, XXY), count the number of X chromosomes (2) and subtract 1 to find the number of Barr bodies: \(\text{Barr bodies} = \text{number of X chromosomes} - 1\).
For Turner syndrome (typically 45, X), there is only one X chromosome, so apply the formula to find the number of Barr bodies.
For the karyotype 47, XYY, note the number of X chromosomes and apply the formula to determine the number of Barr bodies.
For the karyotypes 47, XXX and 48, XXXX, count the X chromosomes and subtract 1 to find the expected number of Barr bodies in each case.

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Barr Body Formation and X-Chromosome Inactivation

Barr bodies are inactivated X chromosomes found in the nuclei of female cells and individuals with extra X chromosomes. This process, called X-chromosome inactivation, ensures dosage compensation by silencing all but one X chromosome in each cell. The number of Barr bodies equals the number of X chromosomes minus one.
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X-Inactivation

Klinefelter Syndrome and Turner Syndrome Karyotypes

Klinefelter syndrome typically involves a 47,XXY karyotype, where one X chromosome is inactivated, resulting in one Barr body. Turner syndrome involves a 45,X karyotype with only one X chromosome, so no Barr bodies are present. Understanding these syndromes helps predict Barr body counts based on sex chromosome composition.
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Human Sex Chromosomes

Sex Chromosome Aneuploidies and Their Impact on Barr Bodies

Aneuploidies like 47,XYY, 47,XXX, and 48,XXXX involve variations in sex chromosome number. In 47,XYY, no Barr bodies form since there is only one X chromosome. In 47,XXX and 48,XXXX, the number of Barr bodies equals the number of X chromosomes minus one, resulting in two and three Barr bodies respectively.
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Human Sex Chromosomes
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