Genetics & Chimerism Science Fair Projects

Nitya
15 years old

Grade 10 Delhi, India

PROJECT RESEARCH CONTENT

It is basically a situation in which an organism has 2 different sets of DNA.

Chimeras are formed from four parent cells (two fertilized eggs or early embryos fused together) or from three parent cells (a fertilized egg is fused with an unfertilized egg or a fertilized egg is fused with an extra sperm). Each population of cells keeps its own character and the resulting animal is a mixture of tissues.

This condition is either inherited, or it is acquired through the infusion of allogeneic hematopoietic cells during transplantation or transfusion. In nonidentical twins, chimerism occurs by means of blood-vessel anastomoses. The likelihood of offspring being a chimera is increased if it is created via in vitro fertilization. Chimeras can often breed, but the fertility and type of offspring depends on which cell line gave rise to the ovaries or testes; varying degrees of intersexuality may result if one set of cells is genetically female and another genetically male.

References from Mythology: In the Iliad Homer described a creature having body parts from different animals, a chimera, from this mythological monster comes the name of the genetic equivalent – chimerism. Chimerism refers to organisms possessing more than one genetic identity. The term “chimera” comes from a mythological composite creature made from parts of other animals.

Chimerism in humans: In humans, a chimera can be the result of two embryos becoming fused. This is considered to be very rare. When two embryos are fused and go on to develop successfully, DNA from each embryo will then be present in that person’s body. Had they not become fused, these embryos would have had the potential to grow into normal fraternal twins.

Genetic chimerism, or tetragametism, in humans and other animals happens when two fertilized eggs or embryos fuse together early in pregnancy. Each zygote carries a copy of its parents DNA and thus a distinct genetic profile. When these merge, each population of cells retains its genetic character and the resulting embryo becomes a mixture of both.

Essentially, a human chimera is their own twin. DNA testing is often used to establish whether a person is biologically related to their parents or children and can uncover cases of chimerism when DNA results show that children are not biologically related to their mothers – because the child inherited a different DNA profile to the one shown by a blood test. What happens of the second fraternal twins life after fusion…do two souls live in a body…or the other soul dies…?

Advantages of being a chimera: Astonishingly chimeras are a gift of nature and are designed for better survival. People born with chimerism typically have immune systems that make them tolerant to both genetically distinct populations of cells in their body. This means that a chimera has a much wider array of people to choose from should they need an organ transplant.

Manifestation of Chimerism in Humans:A person could be a chimera without ever knowing. For example, a chimera could have one organ with different DNA to that in the rest of their body. In some cases, they may have visible signs such as differently-colored eyes. Chimerism can also result in a person with both male and female sexual organs (hermaphrodism).

Recognition of Chimerism: In recent years, media coverage has raised awareness regarding human chimeras. For example, in 1998 a woman named Karen Keegan required an organ transplant and looked to her sons to see if any were a potential match. The testing suggested that she could not be the mother of two of her three sons. Further genetic testing showed that Karen was actually a chimera, and that her sons were all definitely her biological children. Kinds of chimerism:

1. Microchimerism: is the presence of a small number of cells, genetically distinct from those of the host individual. The most common form is fetomaternal microchimerism (or fetal chimerism) whereby cells from a fetus pass through into the mother. Fetal cells have been documented to persist in maternal circulation for as long as 38 years. Micro chimerism had also been shown to exist after blood transfusions to a severely immunocompromised population of patients who suffered trauma.

   Systemic lupus erythematosus: is a chronic autoimmune disease that can be fatal, though with recent medical advances fatalities are becoming increasingly rare. As with other autoimmune diseases, the immune system attacks the body’s cells and tissue, resulting in inflammation and tissue damage. The cause of this disease was unknown for several years but as several mysteries unfold scientists are relating this disorder to Micro chimerism {as they believe that the immune system maybe attacking the foreign cells now a part of the body leading to several complications},hoping to find cures in the future.

2. Tetragametic chimerism: is a less common cause of congenital chimerism. It occurs through the fertilization of two ova by two sperm, followed by the fusion of the zygotes and the development of an organism with intermingled cell lines. This happens at a very early stage of development, such as that of the blastocyst. Such an organism is called a tetragametic chimera as it is formed from four gametes — two eggs and two sperm. Put another way, the chimera is formed from the merger of two fraternal twins in a very early (zygote or blastocyst) phase. As such, they can be male, female, or hermaphroditic.

   Is the third gender {known as hijras in the Indian subcontinent} a form of chimera{formed by the fusion of a male and a female fraternal twin}…?Are they related to the etymological character Hermaphroditus {this is where the term "hermaphrodite" derives from}, the son of Hermes and Aphrodite in Greek mythology, who was fused with a nymph, Salmacis, resulting in one individual possessing physical traits of both sexes…?

3. Parasitic chimerism in anglerfishes: Chimerism occurs naturally in adult Ceratioid anglerfishes and is in fact a natural and essential part of their lifecycle. One or more males attach to a female as parasites (they must do so, as they will never fully mature alone), eventually fusing into a single, hermaphroditic individual with a shared circulatory system. Once fused to a female, the males will reach sexual maturity, developing large testicles as their other organs atrophy.
4. Germline chimerism: is when the sperm and egg cells of an organism are not genetically identical to its own. It has recently been discovered that marmosets {kind of monkeys}can carry the reproductive cells of their twin siblings, because of placental fusion during development.

Continue this project at dual identities science fair experiment.