genetic mosaicism

Mosaics and chimeras are animals that have more than one genetically distinct population of cells

Cytogenetic Mosaics

The term mosaic is usually applied to animals, which is more than one-cytogenetically distinct cell populations. For example, in human mosaic, some cells may be 46, XX and 47, XXX. Part of the cells of each genotype is very variable, reflecting during early embryogenesis of the mosaic of origin. In most but not all cases, the mosaic can be found in the cells of all tissues. What is the clinical significance of mosaicism? If the proportion of cytogenetically abnormal cells in the mosaic is very important, this person will disease manifestations. Conversely, if the abnormal cells are relatively low compared with cytogenetically normal cells, normal cells may be sufficient to prevent disease or reduce its severity. For example, most people with Turner syndrome (monosomy X chromosome) die before birth. Many people who survive Turner mosaics are a significant part of the normal cells (eg 46 XX/45 XO mosaics).

X chromosome mosaicism

In early embryogenesis in mammals, but all have functional X chromosome inactivated through the process of inactivation of chromosome X. Since the inactivation occurs at random, normal all women have approximately equal populations of two genetically different cell types and are therefore a mosaic. In about half of their cells, paternal X chromosome is inactivated, and the other half of the maternal X chromosome is inactive. This has several important biological and medical implications, especially in terms of X-linked genetic diseases. Cats provide a unique opportunity to observe the inactivation of chromosome X and to help visualize how it affects all women. Tortiseshell cats as shown below, have a coating that is a mixture of black and orange hair. American cats are similar, but they also have white spots, which is encoded by a gene. Gene coding for the orange layer is X-linked (which is on chromosome X). Black is coded with co-dominant alel on chromosome X, or, more likely, an autosomal gene that is masked by the orange gene. For explanation, we will consider the orange gene (O) and non-orange alel (v) to be X-linked. Normal males have one X chromosome and can carry or O or O gene, causing them to have a black coat and orange, respectively. Female cats, with two X chromosomes may be one of the three genotypes in comparison with orange gene: OO (orange jacket), OO (black cloak) and Oo (tortiseshell or America). The reason for the fine tortiseshell orange spots and black reflects the structure of X chromosome inactivation in the hair follicles. In black, wore orange X chromosome is switched off alel and X chromosome in non-orange alel is active. Just the opposite is also present in patches of orange fur. In the randomness of X chromosome inactivation is clear - there are relatively large patches of black and orange (for 5 pieces in a row when Display coins), but most of the layer is a perfect combination of orange and black (head, tail, tails, heads tails ...). And what if you're interested in cat coat colors? Maybe not even like cats. Understanding of this information is still important? Yes! Pattern of X chromosome inactivation as seen in black and orange coat of fur of cats tortiseshell present in all tissues of all mammals. This model is usually not visible, as, for example, human skin colors are not encoded by genes associated with X. However, understanding and X chromosome inactivation mosaicism is very important in all species for understanding the pathophysiology of X-linked genetic diseases.
Chimeras

In mythology, A chimera is a monster of a fire made in the breath of a lion head, goat body and tail of the snake. In medical science, A chimera is a person with more than one genetically distinct population of cells that come from more than one zygote.