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<ul><li><p>132</p><p>brothers, one unborn, the chance of neither showing recombinationwhen the recombination fraction is t is 1-2t when t is small: withthree brothers the more substantial data may cause confusion sinceno opinion can be given if the first two are discrepant. The figureshows the error rate, compensated for errors which cancel out, for 2,3, and 4 meiotic separations (e.g., brother, uncle, cousin).Meanwhile, all that can be done is to ensure that after death, or if</p><p>death seems close, DNA is preserved for the benefit of relatives. Anytissue, buffy coat, or even whole blood will be stable if deeply frozen.How deep is unclear, but -20C is sufficient for a month and- 80C for years. Prepared DNA is stable at room temperature.Preparation is not difficult and is a reasonable request to a clinicallaboratory on the rare occasions when indicated. The alternative ofestablished cell lines is more expensive and less reliable. 1 g of tissueshould be more than adequate. For whole blood 1 ml has sufficientDNA for about one track, and 20 ml should be adequate, assumingsubstantial amounts are available from potential female carriersseeking advice.</p><p>Genetics Laboratory,Department of Biochemistry,University of Oxford,Oxford OX 1 3QU J. H. EDWARDS</p><p>HEMISPHERIC ORGANISATION IN 47,XXY BOYS</p><p>SiR,-Dr Netley and Dr Rovet (July 31, p. 267) noted an increasein non-righthandedness in their sample of 33 unselected males witha supernumerary X chromosome and suggested that this, incombination with a previously published visual field study, reflectsfailure to establish left hemisphere dominance for language in menwith a supernumerary X chromosome. In our sample of fourteenunselected 47,XXY boys we do not find similar evidence.The fourteen boys (mean age 12 years) were identified by</p><p>X-chromatin examination on 40 000 consecutive births over a ten</p><p>year period. The fourteen chromosomally normal male controlswere matched for age and socioeconomic status. In both groups,thirteen of the boys were righthanded as measured on six hand uses.Thus, there is no increase of non-right-handedness in the 47,XXYboys. Dichotic listening studies were done by an audiologist; thechild had to repeat correctly a message heard in one ear while</p><p>ignoring a different message heard in the other ear. The significantright ear advantage of the 47,XXY boys (p</p></li></ul>


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