n. (in embryology) the process of repeated cell division of the fertilized egg to form a ball of cells that becomes the *blastocyst. The cells (blastomeres) do not grow between divisions and so they decrease in size.
If non-dysjunction occurs after the formation of a ZYGOTE – that is, during a mitotic cell division and not a meiotic cell division (see MITOSIS; MEIOSIS) – some of the cells will have one chromosome constitution and others another. The term mosaicism describes a condition in which a substantial minority of cells in an individual’s body di?er from the majority in their chromosome content. How substantial this minority is will depend upon how early during cleavage the zygote undergoes nondysjunction. Mosaicism can cause disorders such as DOWN’S (DOWN) SYNDROME and TURNER’S SYNDROME. The proportion and type of abnormal cells affect the physical appearance of the affected individual. This may range from normal to the features typical of people with a chromosomal-abnormality syndrome.... mosaicism
n. an enzyme that catalyses the cleavage of DNA. A genetically engineered form, recombinant human DNAse (dornase alfa), is used in the treatment of *cystic fibrosis to reduce the viscosity of the sticky secretions in the lungs. Administered by inhalation via a jet nebulizer, it appears to hydrolyse extracellular DNA that accumulates with other neutrophil debris in the airways. Trade name: Pulmozyme.... dnase
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