A fluorescent in situ hybridization analysis of X chromosome pairing in early human female meiosis.

Fluorescent in situ hybridization (FISH) utilizating an X chromosome whole library probe was used directly to assess the rate of aneuploidy and pairing behavior of the X chromosome in human female meiosis. Over 3000 meiotic cells obtained from fetal ovaries (gestational age 13-22 weeks) were scored for meiotic stage and evaluated for pairing abnormalities. No pairing anomalies were observed in 832 pachytenes. Twenty-two percent (88/398) of cells in zygotene were partially paired, but nonhomologous pairings could not be identified. One aneuploid preleptotene oocyte, presumably from mitotic nondisjunction was detected. To our knowledge, this is the first report of the use of FISH utilizing whole chromosome probes to evaluate the pairing behavior of chromosomes in human female meiosis. The application of this technique to study the relationship between nondisjunction and chromosome pairing behavior in maternal-age-related aneuploidy is discussed.