Genetic Mosaicism

Question 1

Genetic Mosaicism

Answer 1

Presence in an individual or tissue of at least two cell lineages that differ genetically but are derived from a single zygote

Question 2

Confined Placental Mosaicism

Answer 2

Mutation found only in extraembryonic tissue and not in the embryo proper. Can result in a normal pregnancy outcome or is sometimes associated with delayed growth of the fetus

Question 3

(Pure) Somatic Mosaicism

Answer 3

Mutation is present in some tissues of the embryo but not in the gametes. Phenotype affects the individual, but mutation would not be passed on to future offspring

Question 4

(Pure) Germline Mosaicism

Answer 4

Mutation is restricted to the gamete lineage only. Must arise after somatic and germline cells have separated lineages. For many diseases, the individual is not affected but is at risk of passing the mutation and producing affected offspring

Question 5

Combination Mosaicism

Answer 5

Mutation can be present in both somatic and germline lineages. Depends on whether the mutation occured before or after the separation of the inner cell mass, the germline cells, and the somatic cells during embryologenesis

Question 6

Mosaic Down Syndrome

Answer 6

Mixture of cells (disomic and trisomeic) for chromosome 21. Arises due to non-disjunction events involving chromosome 21 during mitotic division in the early embryo. These individuals typically have a less severe phenotype.