Knowra Mosaicism Mosaicism Mosaicism is the presence of genetically distinct cell populations within one organism. The populations arise from a single fertilized egg and can differ in genetic makeup or chromosome number.
Somatic mutation : A DNA sequence change acquired by a cell after fertilization and passed to its descendants. A mutation in an embryonic cell can create a genetically distinct lineage.
McCune–Albright syndrome : A disorder involving patchy skin pigmentation, bone abnormalities, and endocrine overactivity, often caused by mosaic GNAS mutations. Its symptoms reflect where a postzygotic mutation-bearing lineage expanded.
Genetic testing : Laboratory analysis of DNA, chromosomes, or gene products to identify genetic variation. Test results depend on whether sampled tissue contains the altered cell lineage.
Zygote : The diploid cell formed when sperm and egg unite at fertilization. Mosaic lineages usually begin with mutations arising after this single-cell stage.
Single-cell sequencing : Methods that determine DNA or RNA sequences in individual cells. Analyzing cells separately can reveal variants hidden by bulk-tissue averages.
Mitotic recombination : Exchange of DNA between homologous chromosomes during mitosis, sometimes producing genetically distinct daughter-cell lineages. This process can generate mosaic patches with different inherited chromosome segments.
Mosaic Down syndrome : A form of Down syndrome in which some cells have trisomy 21 and others have the usual chromosome count. It results when chromosome 21 separation differs among early cell lineages.
Variant allele frequency : The proportion of sequencing reads at a genomic position that carry a particular variant. A reduced allele fraction can signal a mosaic variant, though technical and biological factors also affect it.
Embryonic development : The process by which an embryo grows and differentiates into tissues and organs. Cell division and lineage allocation during development distribute mosaic variants.
Tissue-specific mosaicism : Mosaic genetic variation confined to, or enriched in, particular tissues. Blood may not reveal variants present in brain, skin, or other organs.
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