What does the term "mosaicism" refer to in preimplantation genetic testing?

Mosaicism, in the context of preimplantation genetic testing, refers to the presence of genetic variants in a subset of cells. This phenomenon occurs when there are two or more genetically different cell populations within the same individual, resulting from a mutation that happens during early embryonic development. In preimplantation genetic testing, identifying mosaicism is crucial because it can impact the development and viability of the embryo, as well as the potential for a genetic condition to manifest if the embryo is implanted.

Recognizing mosaicism is important for genetic counselors and clinicians, as it aids in making informed decisions regarding embryo selection for implantation. An embryo with some cells showing a genetic abnormality alongside normal cells may still be viable and lead to a healthy pregnancy, depending on the proportion and distribution of the affected cells.

The other options do not accurately capture the definition of mosaicism. Variations between maternal and fetal chromosomes refer to the differences that can arise from the maternal contribution but do not inherently speak to the concept of mosaicism. The notion of multiple maternal genetic conditions does not relate directly to the structural or genetic makeup of the embryo itself. Lastly, "only euploid embryos" implies the absence of any chromosomal variations, which contradicts the essence of mosaicism that