Although the X chromosome is usually similar to the autosomes in size, gene density and cytogenetic appearance, theoretical models predict that its hemizygosity in males may cause unusual patterns of evolution. The sequencing of several genomes has indeed revealed differences between the X chromosome and the autosomes in the rates of gene divergence, patterns of gene expression and rates of gen...

Serum levels of immunoglobulins (Ig) G, M, and A were determined in 28 women with an additional X-chromosome (XXX), and in equal numbers of age-matched normal women and men. Mean IgM levels were found to be highest in the XXX group, intermediate in normal women, and lowest in men; these differences were statistically significant. Mean IgM values obtained from seven XXY and three XXXY cases were...

I many organisms, differentiation of the sex chromosome complement resulted in the coordinated regulation of genes on whole chromosomes to equalize gene expression between the sexes. In mammals, X inactivation evolved to restore equal expression of X-linked genes in males and females (1). Although X inactivation consists in the general repression of most genes on the X, some genes escape inacti...

Non-random X-chromosome inactivation in mammals was one of the first observed examples of differential expression dependent on the gamete of origin of the genetic material. The paternally-inherited X chromosome is preferentially inactive in all cells of female marsupials and in the extra-embryonic tissues of developing female rodents. Some form of parental imprinting during male and female game...

Mouse genetic studies using Robertsonian and reciprocal translocations have shown that certain autosomal regions of loci are subject to a parental germ line imprint, which renders maternal and paternal copies functionally inequivalent in the embryo or later stages of development. Duplication of maternal or paternal copies with corresponding paternal/maternal deficiencies in chromosomally balanc...

HROMOSOME 1 of Spinacia oleracea, the longest of the complement, con'tains the "alleles" X , X", and Y , that effect sex determination (ELLIS and JANICK 1960; SUTO and SUGIYAMA 1961; IIZUKA and JANICK 1962). The genotype X X is pistillate, X"X and X"X" are potentially monoecious (although X"Xm is more highly male), and X Y and X"Y are staminate. The standard chromosome 1 is heterobrachial with ...

The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from 12 1/2-day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1). If such germ cells carry the preferentially active Searle's translocated X chromosome (Lyon, Searle, Ford & Ohno, 1964), then only the Pgk-1 allele on this chrom...

In the present investigation the transcription and replication patterns have been examined in different segments of the X chromosome and in certain specific segments (88B-92A) of an autosomal segmental hyperploid in which an extra segment 88B-92A (3R) is translocated to the X chromosome in addition to the normal two doses. Transcriptive activity monitored by [3H]uridine-labelling of these autos...

A mentally retarded male patient with a structurally abnormal X chromosome is reported (karyotype 46, dir dup (X)(p11.2 leads to p21.2)Y). In the normal mother a similar X chromosome duplication was found, which was preferentially inactivated. Xg blood groups were studied in the family. The findings indicated that recombination took place at maternal meiosis, as both karyotypically normal sons ...