is an intermediate phase between diplotene and metaphase of the first mei-
otic division.
69.The answer is b.(Kasper, p 2215. Sadler, pp 18–19, 251. Moore and
Persaud, Developing, p 165.)Cells from a patient with the most common
form of Klinefelter’s syndrome (47,XXY genotype) will have one inactive X
chromosome and, therefore, one Barr body. The formula is the number of
Barr bodies equals the number of X chromosomes minus one. Klinefelter’s
syndrome occurs at a ratio of about 1:500 males and is due to meiotic
nondisjunction of the chromosomes. The nondisjunction is more frequent
in oogenesis than in spermatogenesis, and increased occurrence is directly
proportional to increasing maternal age. Klinefelter’s may occur as 47,XXY,
48,XXYY, 48,XXXY, and 49,XXXXY. A combination of abnormal and nor-
mal genotype occurs in mosaic individuals who generally have less severe
symptoms. Females have two X chromosomes, one of maternal and the
other of paternal origin. Only one of the X chromosomes is active in the
somatic, diploid cells of the female; the other X chromosome remains inac-
tive and is visible in appropriately stained interphase cells as a mass of het-
erochromatin. Detection of the Barr body (sex chromatin) has been an
efficient method for the determination of chromosomal sex and abnormal-
ities of X-chromosome number; however, it is not definitive proof of male-
ness or femaleness. The genotypic sex of Klinefelter’s syndrome and XXX
individuals would be male and female as determined by the presence or
absence of the testis-determining Y chromosome. In Turner’s syndrome
(XO), no Barr bodies would be present. In comparison, “superfemales”
(XXX) would possess two inactive X chromosomes (2 Barr bodies) and one
active X chromosome. Buccal scrapings for Barr body analysis are being
used less—chromosomal analysis is the standard test now.
70.The answer is e.(Kasper, p 1382. Rubin, p 37.)In Hutchinson-Gilford
progerial syndrome (HGPS) an abnormal protein, progerin, is generated
and has a “dominant negative” effect on the function of lamins. The lamins
are intermediate filament proteins that regulate the nuclear envelope,
maintain its stability, and are phosphorylated (prometaphase) and dephos-
phorylated (telophase) during the cell cycle. In HGPS the results are dra-
matic abnormalities in the architecture of the nucleus, changes in nuclear
shape, loss of heterochromatin (unable to attach to lamins), and an altered
distribution of nuclear proteins (answer a).Microtubule treadmilling
Cell Biology: Nucleus Answers 151