Chromosomal Mosaicism

A third embryonic hemoglobin, termed Hb-Portland 1, has recently been described (Cl, C2, H6, T8, W17). The protein was first discovered in a malformed newborn with a complex autosomal chromosomal mosaicism. However, it is probably also present for some 0.5 to 5% in newborn infants with a D, trisomy and in very small amounts (0.1-0.2%) in normal newborns. Hb-Portland 1 does not contain a chains but is composed of one pair of y chains and one pair of chains which have been termed C chains. The C chain is probably a normal embryonic hemoglobin chain. Hb-Portland 1 does react with free a chains to form Hb-F or aayz and a aafa component (T8). It seems, therefore, that the chain can combine with the a chain, but the afiSnity of the a chain for the C chain is apparently lower than for either the e chain or y chain. Embryonic hemoglobins have also been found in several mammalian species, such as the pig, cattle, and sheep (K13, K15). 

Congenital adrenal hyperplasia Congestive heart failure Chromosome disorders Chromosome mosaicism Chromosome translocation Copper excess Cri-du-chat syndrome Crouzon s syndrome Cushing s syndrome Cyanide poisoning Cystic fibrosis Diabetes insipidus Diabetes mellitus Dinitrophenol poisoning Diphtheria... 

Aneuploidy is consequential to mitotic errors malignantly transformed cells frequently commit mitotic errors. In fetal life, the developing human brain suffers of chromosomal segregational defects during mitoses of glial cells and neurons. Aneuploid brain cells are eliminated by apoptosis. Areas not cleared by apoptosis, remain confined to sites of chromosomal mosaicism. The presence of functionally active aneuploid neurons negatively affect neuron-to-neuron and neuron-to-gUal interactions [1291]. 

Yurin YB, lourov lY, Vorsanova SG, Liehr T, Kolotii AD, Kutsev SI, Pellestor F, Beresheva AK, Demidova lA, Kravets VS, Monakhov VV, Soloviev IV. Aneuploidy and confined chromosomal mosaicism in the developing human brain. PLoS One. 2007 2(6) c558. doi 10.1371/journal.pone.000558. 

I am not concerned here with phenomena relating to somatic mutation of cells, the formation of chromosomal mosaics and chimeras, of tumors, and so on, or with other cases going beyond the bounds of normal development. 

Detection of chromosome fragments. Individuals with Turner s syndrome are, in some cases, mosaic for a portion of or for the entire Y chromosome (46,XY/45,X). Since such individuals may be at increased risk for gonadal tumors, Southern blot or PCR analysis has been used to detect the presence of Y chromosome segments in studies of DNA from peripheral blood samples. Similarly, the fetal sex as well as the presence of some aneuploid states (e.g., trisomy 18) can be determined by analysis of DNA from chorionic villi or amniotic fluid cells. 

Mosaicism The occurrence in an individual of two or more cell populations of different chromosomal constitutions, derived from a single zygote, as opposed to chimerism in which the different cell populations are derived from more than one zygote. [NIH]... 

All females are technically mosaic for the genes of their X chromosomes due to inactivation of one or the other X chromosomes early in development, a phenomenon termed the Lyon hypothesis or lyonization. 

W Martin. Mosaic bacterial chromosomes a challenge en route to a tree of genomes. Bioessays 21 99-104, 1999. 

Klinefelter s syndrome (47, XXY) and mosaics Autosomal and sex chromosomes, polyploidies True hermaphroditism Defective androgen biosynthesis... 

Evidence for inactivation of one X chromosome in XX females comes from the observation that females are mosaic for X-linked alleles that are heterozygous. For example, a woman who is heterozygous for a gene that controls production of sweat glands has patches of skin that perspire and patches that do not. Cells in the patches of skin... 

The answer is d. (Murray, pp 812—828. Scriver, pp 3-45. Sack, pp 57-84. Wilson, pp 123—148.) The case described represents one of the more common chromosomal causes of reproductive failure. Turner mosaicism. Turner s syndrome represents a pattern of anomalies including short stature, heart defects, and infertility. Turner s syndrome is often associated with a 45,X karyotype (monosomy X) in females, but mosaicism (i.e., two or more cell lines with different karyotypes in the same individual) is common. However, chimerism (i.e., two cell lines in an individual arising from different zygotes, such as fraternal twins who do not separate) is extremely rare. Trisomy refers to three copies of one chromosome, euploidy to a normal chromosome number, and monoploidy to one set of chromosomes (haploidy in humans). 

Hesselbarth J, Schwarz S (1995) Comparative ribotyping of Staphylococcus intermedius from dogs, pigeons, horses and mink. Vet Microbiol 45 11-17 Heusser R, Ender M, Berger-Bachi B, McCallum N (2007) Mosaic staphylococcal cassette chromosome mec containing two recombinase loci and a new mec complex, B2. Antimicrob Agents Chemother 51 390-393... 

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