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15 The Discovery of Human Sex Chromosome Conditions When Michael Frederic Guyer (1874–1959) looked at human chromosomes in 1910, he estimated the diploid number was 24 in females and 23 in males.1 He thought the sex chromosome mechanism was XX female and XO male. Two years later, Hans Jean Chrysostome von Winiwater (1875–1949) doubled that estimate and claimed the human chromosome number was 47 in spermatocytes, but he agreed with Guyer about the XO status of males.2 That changed in 1921, when Theophilus Shickel Painter (1889–1969) at the University of Texas reported a chromosome number of 48 (although he said it could be 46 or 47). Painter used testes from freshly executed prisoners or from castrated patients in mental asylums. He also said there was a definite Y chromosome in the male cellshestudiedandthus48,XYwasthechromosomenumberandsexual status of males for another generation.3 The status remained stable because techniques did not change in cytology for human cells until the 1950s, when tissue culture techniques improved, hypotonic solutions were used to increase the volume of nuclei , and colchicine was used to arrest cell division at metaphase. In 1956, when two Swedish investigators, Joe Hin Tjio and Albert Levan, combined all these procedures, they got a consistent reading of 46 chromosomes , with very clear XX females and XY males.4 From then on, the human chromosome number was represented as 46,XX for females and 46,XY for males. By 1960, a standardized way of photographing, enlarging , and clipping out chromosomes was introduced. The chromosomes were measured and aligned in size, place, and by grouping within a particularsizerangeofthelocationofthecentromerethatseparatesthetwo The Discovery of Human Sex Chromosome Conditions 105 armsofthechromosomes.(Theshorterarmofthechromosomeiscalled “p” and the longer arm “q.”) The resulting mounted representation of the chromosomesiscalledakaryotype.TheXchromosomeisintheCgroup (chromosomesofmoderatesize),andit isslightlysubmetacentric.TheY chromosome is very small, and the q arm is at least twice as long as the p arm. In 1964, Lionel Sharples Penrose (1898–1972) estimated that the X accounted for about 6 percent of the total DNA of the sperm nucleus in humans, and the Y accounted for about 2 percent.5 Thefirstdeparturefromthistypicalchromosomenumberfoundwas the 47,XXY karyotype, discovered by Patricia Jacobs and J. A. Strong in 1959. This is the chromosome number found in males with Klinefelter syndrome. In 1947, Harry Fitch Klinefelter described such patients as having enlarged breasts, a smaller penis, smaller testes, no spermatozoa, and elevated levels of follicle stimulating hormone.6 He also noted that such patients were slower in learning than other males of their age. The breast enlargement occurred during and after puberty. In 1954, several physicians reported the presence of sex chromatin in the cells of males with Klinefelter syndrome. This was an exception to Murray Barr’s findingthatsexchromatinwasfoundinfemalesbutnotinmales .In1959,that puzzlewasresolvedwhenJacobsandStrongreportedtheircaseofamale with Klinefelter syndrome who had a 47,XXY karyotype.7 The period between 1957, when Jerome Lejeune and Raymond Turpin discovered that Down syndrome (which was still called mongolism ormongoloididiocyatthattime)iscausedbyatrisomyforchromosome 21, and 1965 was a fruitful one for genetic research. In these eight years, a number of autosomal and sex chromosome anomalies were discovered andwrittenabout.Massscreeningofchromosomenumbercouldbecarried out in hospitals and prisons, and each condition that seemed like a likelycandidateforchromosomeanalysiswasputtothetest.Turnersyndrome was the second sexual condition that was recognized as having a chromosomal cause. It gets its name from Henry Turner (1892–1970) who first described females with this condition in 1938.8 He identified small size, absence of breast development, webbing of the neck, and streak ovaries as characteristics of these women. In the mid 1950s, they too turned out to be exceptions to Barr’s findings, as their cells are chromatinnegative .In1959,bothCharlesEdmundFordandMarcoFracarro 106 The 7 Sexes independently reported that Turner females are 45,X (XO).9 In the next few years, a flurry of papers reported conditions of 46,X (XR) females with a normal X, and a companion rearranged X (XR) that was either a partially deleted X, a ring X, or an isoXq chromosome that lacked the p arms of the X. Symptoms of Turner syndrome were present in patients witheachofthesechromosomalvariations.Similarly,thereareinstances ofTurnersyndromewithanXandanaccompanyingisoYqchromosome, or ring Y chromosome, giving 46,X (YR) where YR represents some sort of aberration, with an absence of the p arm of the Y chromosome. Some mosaics are XY/XO. Many others are XX/XO or variations in which some key genes in the p arm of either the X chromosome or Y chromosome are missing. These individuals range from normal females to Turner females, and a few of them exhibit features of...


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