The key difference between chimera and mosaic is the number of zygotes involved in the formation of each organism. Different cell populations originate from two zygotes in chimera while different cell populations originate from a single zygote in mosaic.
Chimera and mosaic were initially mythical concepts of genetic combination. However, with the advancement of genetics and molecular biology, it has now been possible to scientifically explain the phenomena of chimerism and mosaicism. In both chimerism and mosaicism, some of the body cells carry a different genome. Thus, the same tissue may contain two or more different cell populations. Further, two zygotes participate in the formation of an embryo which develops into chimera while a single zygote participates in the formation of an embryo which develops into the mosaic. Mutation in early development is the reason for mosaicism while the involvement of two different zygotes is the reason for chimerism.
CONTENTS
1. Overview and Key Difference
2. What is Chimera
3. What is Mosaic
4. Similarities Between Chimera and Mosaic
5. Side by Side Comparison – Chimera vs Mosaic in Tabular Form
6. Summary
What is Chimera?
Chimera is an organism made by the combination of two different zygotes. Here, two distinct zygotes fuse within a single embryo. So, this is a phenomenon called chimerism. The presence of 46 X.X and 46X.Y recognizes chimerism. It may trigger clinically or cytogenetically. However, in the case of a chimera without a sex chromosome constitution, it is difficult to identify. In such cases, molecular identification of the chimera is important. Single Nucleotide Polymorphism (SNP) analysis plays an important role in the identification of chimera. Further, this technique also identifies the abnormalities present within a chimera.
Figure 01: Chimera
In mythology, the chimera refers to a creature who had body parts from a goat, a lion, and a serpent. However, this concept explains the mixing of two zygotes, which is the genetic explanation for the mythical scenario.
What is Mosaic?
Mosaic organisms are organisms having two or more different chromosomal complements from distinct cell lines. However, both chromosome complements develop from a single zygote and then develops into a mosaic embryo. It is a phenomenon called mosaicism. Mosaic organisms frequently report chromosomal abnormalities such as trisomy, monosomy, triploidy, and other chromosomal structural aberrations. Therefore, Mosaicism plays a major role in determining the genetic basis of diseases.
Figure 02: Mosaic
Mosaic organisms arise from meiotic events that take place during cell division. It may result in abnormal zygote development. Other effects of Mosaicism are X chromosome inactivation and the onset of viral infections.
What are the Similarities Between Chimera and Mosaic?
- Chimera and mosaic may result from genetic mutations.
- Both involve meiosis.
- Molecular techniques are used for the identification of chimera and the mosaic.
What is the Difference Between Chimera and Mosaic?
Chimera and mosaic are organisms that develop due to genetic combinations. The key difference between chimera and mosaic is the number of zygotes involved in embryonic development. In chimera, the fusion of two zygotes takes place while in mosaic, only one zygote participates in the formation of the mosaic embryo. Therefore, at least four parents participate in forming chimera while two parents participate in forming a mosaic.
The below infographic summarizes the difference between chimera and mosaic.
Summary – Chimera vs Mosaic
Chimera and mosaic explain various genetic combinations that take place during development. Initially, they were mythical concepts. However, with the advancement of science and genetics, scientists provide genetic explanations to these concepts. In this regard, a chimera is an organism that originates upon the fusion of two zygotes. In contrast, a mosaic is an organism that originates with the combination of two distinct cell lines of one zygote. They bring about genetic mutations and chromosomal aberrations. Due to this reason, these phenomena are of great scientific interest. So, this summarizes the difference between chimera and mosaic.
Reference:
1. Niu, Dau-Ming, et al. “Mosaic or Chimera? Revisiting an Old Hypothesis about the Cause of the 46,XX/46,XY Hermaphrodite.” The Journal of Pediatrics, U.S. National Library of Medicine, June 2002, Available here.