Mosaicism and chimerism

cytogenetics- explanation on mosaicism and chimerism. And genetic difference between mosaic and chimera; full mosaic and partial mosaic.

1. MOSAICISM AND CHIMERISM S. SHANMUGAPRIYA, Final Year, Biomedical sciences, Sri ramachandra university.

2. MOSAICISM AND CHIMERISM

3. MOSAICISM AND CHIMERISM Mosaicism and chimerism refers to one organism with two or more distinct populations of cells. But they are two different concepts.  Because mosaics start with the same genome, but chimeras is a fusion of two different genomes. Mosaicism and chimerism differ in the mechanisms by which each is prevented

4. MOSAICISM Mosaicism is a condition in which presence of two or more chromosomal complements found in the same tissue of an individual where cells derived from the same genetic origin/same zygotic genotype . This can occur in any type of cells.

5. Mosaicism can arise when there is a mutation in early development so there can be group of cells that behave differently. This can happen on a gene level or even whole chromosomes . For example, a girl has a mixture of 45X and 46XY cells in her body. One cell early in development dropped the Y chromosome and the majority of her cells are 45X. Pattern of inheritance : Both autosomal dominant and recessive

6. Mechanism Of Mosaic Formation

7. Complete and partial mosaic

8. Types of mosaicism Germinal mosaicism Somatic mosaicism Germinal and somatic mosaicism Germinal mosaicism: Asymptomatic , only germinal cells are affected, could be transmitted to progeny E.g.: DMD, Turner syndrome, Hemophilia Somatic mosaicism: Symptomatic Somatic cells are affected It is not inherited

9. Non disjunction

10. E.g : cancer, down syndrome Germinal and somatic mosaicism: presence of both somatic and germline mosaic. Diagnosis: FISH, Karyotype Impact of mosaic on disease: depends on stage of mutation, nature of chromosomal abnormality, proportion between mosaic and normal cells, nature of affected cells. Disease: Heteroplasmy : somatic mosaicism results in random segregation and propagation of mutant mitochondria. Cancer: several recent studies shows that probability of cancer progression depends on the degree of mosaicism.

11. CHIMERISM Chimerism is a condition in which presence of two or more chromosomal complements found in the same tissue of an individual where cell line not derived from a single zygote. Chimeras can happen with organ transplantation (because the donor cells are different from recipient), twin (a pregnancy may start out with two or more zygotes but not all survive and are then absorbed by remaining fetus). In chimerism the divergent genotypes are usually found in all across the genome . Chimerism leads to the dilemma in sex determination.

12. Types of chimerism Artificial chimerism: via blood transfusion, organ, stem cell and bone marrow transplantation. Twin/ multiple gestation: via trans placental passage of second cell line. In naturally occurring chimerism XX/XY is highly frequent. It is increases with increase in IVF birth Tetragametic : via fusion of two fertilized zygote.

13. Types of natural chimera: Fetal- maternal chimera Blood sharing and twin chimera Whole body or dispermic chimera Tumor chimera Germ cell chimera

14. Test to done before transplantation are, HLA, red cells phenotype studies, peripheral blood and skin fibroblast karyotyping, FISH study.

15. References Mosaicism and chimerism as components of intraorganismal genetic heterogeneity, B.SANTELICES , J . EVOL. B IOL. 17 (2004 ) 1187–1188 Mechanisms of mosaicism, chimerism and uniparental disomy identified by single nucleotide polymorphism array analysis Laura K. Conlin , Brian D. Thiel, Carsten G. Bonnemann , Livija Medne , Linda M. Ernst, Elaine H. Zackai , Matthew A. Deardorff , Ian D. Krantz , Hakon Hakonarson and Nancy B. Spinner www.genegeek.com OMIM