Chimera (genetics)

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This article is about genetic chimærism. Chimera (genetics)_sentence_0

For the cartilaginous fish, see Chimaera. Chimera (genetics)_sentence_1

For the mythological beast, see Chimera (mythology). Chimera (genetics)_sentence_2

A genetic chimerism or chimera (/kaɪˈmɪərə/ ky-MEER-ə or /kɪˈmɪərə/ kə-MEER-ə, also chimaera (chimæra)) is a single organism composed of cells with more than one distinct genotype. Chimera (genetics)_sentence_3

In animals, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types, subtle variations in form (phenotype) and, if the zygotes were of differing sexes, then even the possession of both female and male sex organs (this is just one of many different phenomena that may result in intersexuality). Chimera (genetics)_sentence_4

Animal chimeras are produced by the merger of multiple fertilized eggs. Chimera (genetics)_sentence_5

In plant chimeras, however, the distinct types of tissue may originate from the same zygote, and the difference is often due to mutation during ordinary cell division. Chimera (genetics)_sentence_6

Normally, genetic chimerism is not visible on casual inspection; however, it has been detected in the course of proving parentage. Chimera (genetics)_sentence_7

Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from a different genome. Chimera (genetics)_sentence_8

For example, transplantation of bone marrow often determines the recipient's ensuing blood type. Chimera (genetics)_sentence_9

Animals Chimera (genetics)_section_0

An animal chimera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. Chimera (genetics)_sentence_10

If the different cells have emerged from the same zygote, the organism is called a mosaic. Chimera (genetics)_sentence_11

Chimeras are formed from at least four parent cells (two fertilised eggs or early embryos fused together). Chimera (genetics)_sentence_12

Each population of cells keeps its own character and the resulting organism is a mixture of tissues. Chimera (genetics)_sentence_13

Cases of human chimerism have been documented. Chimera (genetics)_sentence_14

This condition is either inherited or it is acquired through the infusion of allogeneic hematopoietic cells during transplantation or transfusion. Chimera (genetics)_sentence_15

In nonidentical twins, chimerism occurs by means of blood-vessel anastomoses. Chimera (genetics)_sentence_16

The likelihood of offspring being a chimera is increased if it is created via in vitro fertilisation. Chimera (genetics)_sentence_17

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 intersex differences may result if one set of cells is genetically female and another genetically male. Chimera (genetics)_sentence_18

Tetragametic chimerism Chimera (genetics)_section_1

Tetragametic chimerism is a form of congenital chimerism. Chimera (genetics)_sentence_19

This condition occurs through the fertilization of two separate ova by two sperm, followed by aggregation of the two at the blastocyst or zygote stages. Chimera (genetics)_sentence_20

This results in the development of an organism with intermingled cell lines. Chimera (genetics)_sentence_21

Put another way, the chimera is formed from the merging of two nonidentical twins (a similar merging presumably occurs with identical twins, but as their genotypes are not significantly distinct, the resulting individual would not be considered a chimera). Chimera (genetics)_sentence_22

As such, they can be male, female, or have mixed intersex characteristics. Chimera (genetics)_sentence_23

As the organism develops, it can come to possess organs that have different sets of chromosomes. Chimera (genetics)_sentence_24

For example, the chimera may have a liver composed of cells with one set of chromosomes and have a kidney composed of cells with a second set of chromosomes. Chimera (genetics)_sentence_25

This has occurred in humans, and at one time was thought to be extremely rare although more recent evidence suggests that this is not the case. Chimera (genetics)_sentence_26

This is particularly true for the marmoset. Chimera (genetics)_sentence_27

Recent research shows most marmosets are chimeras, sharing DNA with their fraternal twins. Chimera (genetics)_sentence_28

95% of marmoset fraternal twins trade blood through chorionic fusions, making them hematopoietic chimeras. Chimera (genetics)_sentence_29

Most chimeras will go through life without realizing they are chimeras. Chimera (genetics)_sentence_30

The difference in phenotypes may be subtle (e.g., having a hitchhiker's thumb and a straight thumb, eyes of slightly different colors, differential hair growth on opposite sides of the body, etc.) or completely undetectable. Chimera (genetics)_sentence_31

Chimeras may also show, under a certain spectrum of UV light, distinctive marks on the back resembling that of arrow points pointing downwards from the shoulders down to the lower back; this is one expression of pigment unevenness called Blaschko's lines. Chimera (genetics)_sentence_32

Affected persons may be identified by the finding of two populations of red cells or, if the zygotes are of opposite sex, ambiguous genitalia and intersex alone or in combination; such persons sometimes also have patchy skin, hair, or eye pigmentation (heterochromia). Chimera (genetics)_sentence_33

If the blastocysts are of opposite sex, genitals of both sexes may be formed: either ovary and testis, or combined ovotestes, in one rare form of intersex, a condition previously known as true hermaphroditism. Chimera (genetics)_sentence_34

Note that the frequency of this condition does not indicate the true prevalence of chimerism. Chimera (genetics)_sentence_35

Most chimeras composed of both male and female cells probably do not have an intersex condition, as might be expected if the two cell populations were evenly blended throughout the body. Chimera (genetics)_sentence_36

Often, most or all of the cells of a single cell type will be composed of a single cell line, i.e. the blood may be composed predominantly of one cell line, and the internal organs of the other cell line. Chimera (genetics)_sentence_37

Genitalia produce the hormones responsible for other sex characteristics. Chimera (genetics)_sentence_38

Natural chimeras are almost never detected unless they exhibit abnormalities such as male/female or hermaphrodite characteristics or uneven skin pigmentation. Chimera (genetics)_sentence_39

The most noticeable are some male tortoiseshell cats and calico cats (although most male tortoiseshells have an extra X chromosome responsible for the colouration) or animals with ambiguous sex organs. Chimera (genetics)_sentence_40

The existence of chimerism is problematic for DNA testing, a fact with implications for family and criminal law. Chimera (genetics)_sentence_41

The Lydia Fairchild case, for example, was brought to court after DNA testing apparently showed that her children could not be hers. Chimera (genetics)_sentence_42

Fraud charges were filed against her and her custody of her children was challenged. Chimera (genetics)_sentence_43

The charge against her was dismissed when it became clear that Lydia was a chimera, with the matching DNA being found in her cervical tissue. Chimera (genetics)_sentence_44

Another case was that of Karen Keegan, who was also suspected (initially) of not being her children's biological mother, after DNA tests on her adult sons for a kidney transplant she needed seemed to show she was not their mother. Chimera (genetics)_sentence_45

The tetragametic state has important implications for organ or stem cell transplantation. Chimera (genetics)_sentence_46

Chimeras typically have immunologic tolerance to both cell lines. Chimera (genetics)_sentence_47

Microchimerism Chimera (genetics)_section_2

Main article: Microchimerism Chimera (genetics)_sentence_48

Microchimerism is the presence of a small number of cells that are genetically distinct from those of the host individual. Chimera (genetics)_sentence_49

Most people are born with a few cells genetically identical to their mothers' and the proportion of these cells goes down in healthy individuals as they get older. Chimera (genetics)_sentence_50

People who retain higher numbers of cells genetically identical to their mother's have been observed to have higher rates of some autoimmune diseases, presumably because the immune system is responsible for destroying these cells and a common immune defect prevents it from doing so and also causes autoimmune problems. Chimera (genetics)_sentence_51

The higher rates of autoimmune diseases due to the presence of maternally-derived cells is why in a 2010 study of a 40-year-old man with scleroderma-like disease (an autoimmune rheumatic disease), the female cells detected in his blood stream via FISH (fluorescence in situ hybridization) were thought to be maternally-derived. Chimera (genetics)_sentence_52

However, his form of microchimerism was found to be due to a vanished twin, and it is unknown whether microchimerism from a vanished twin might predispose individuals to autoimmune diseases as well. Chimera (genetics)_sentence_53

Mothers often also have a few cells genetically identical to those of their children, and some people also have some cells genetically identical to those of their siblings (maternal siblings only, since these cells are passed to them because their mother retained them). Chimera (genetics)_sentence_54

Symbiotic chimerism in anglerfish Chimera (genetics)_section_3

Chimerism occurs naturally in adult Ceratioid anglerfish and is in fact a natural and essential part of their life cycle. Chimera (genetics)_sentence_55

Once the male achieves adulthood, it begins its search for a female. Chimera (genetics)_sentence_56

Using strong olfactory (or smell) receptors, the male searches until it locates a female anglerfish. Chimera (genetics)_sentence_57

The male, less than an inch in length, bites into her skin and releases an enzyme that digests the skin of both his mouth and her body, fusing the pair down to the blood-vessel level. Chimera (genetics)_sentence_58

While this attachment has become necessary for the male's survival, it will eventually consume him, as both anglerfish fuse into a single hermaphroditic individual. Chimera (genetics)_sentence_59

Sometimes in this process, more than one male will attach to a single female as a symbiote. Chimera (genetics)_sentence_60

In this case, they will all be consumed into the body of the larger female angler. Chimera (genetics)_sentence_61

Once fused to a female, the males will reach sexual maturity, developing large testicles as their other organs atrophy. Chimera (genetics)_sentence_62

This process allows for sperm to be in constant supply when the female produces an egg, so that the chimeric fish is able to have a greater number of offspring. Chimera (genetics)_sentence_63

Germline chimerism Chimera (genetics)_section_4

Germline chimerism occurs when the germ cells (for example, sperm and egg cells) of an organism are not genetically identical to its own. Chimera (genetics)_sentence_64

It has been recently discovered that marmosets can carry the reproductive cells of their (fraternal) twin siblings due to placental fusion during development. Chimera (genetics)_sentence_65

(Marmosets almost always give birth to fraternal twins.) Chimera (genetics)_sentence_66

Artificial chimerism Chimera (genetics)_section_5

Artificial chimerism falls under the artificial category in which a chimera can exist. Chimera (genetics)_sentence_67

An individual that falls under this classification possesses two different sets of genetic pedigrees: one that was inherited genetically at the time of the formation of the human embryo and the other that was intentionally introduced through a medical procedure known as transplantation. Chimera (genetics)_sentence_68

Specific types of transplants that could induce this condition include bone marrow transplants and organ transplants, as the recipient’s body essentially works to permanently incorporate the new blood stem cells into it. Chimera (genetics)_sentence_69

An example of artificial chimerism in animals are the quail-chick chimeras. Chimera (genetics)_sentence_70

By utilizing  transplantation and ablation in the chick embryo stage, the neural tube and the neural crest cells of the chick were ablated, and replaced with the same parts from a quail. Chimera (genetics)_sentence_71

Once hatched, the quail feathers were visibly apparent around the wing area, whereas the rest of the chick’s body was made of its own chicken cells. Chimera (genetics)_sentence_72

Humans Chimera (genetics)_section_6

Chimerism has been documented in humans in several instances. Chimera (genetics)_sentence_73

Chimera (genetics)_unordered_list_0

  • The Dutch sprinter Foekje Dillema was expelled from the 1950 national team after she refused a mandatory sex test in July 1950; later investigations revealed a Y-chromosome in her body cells, and the analysis showed that she was probably a 46,XX/46,XY mosaic female.Chimera (genetics)_item_0_0
  • In 1953 a human chimera was reported in the British Medical Journal. A woman was found to have blood containing two different blood types. Apparently this resulted from her twin brother's cells living in her body. A 1996 study found that such blood group chimerism is not rare.Chimera (genetics)_item_0_1
  • Another report of a human chimera was published in 1998, where a male human had some partially developed female organs due to chimerism. He had been conceived by in-vitro fertilization.Chimera (genetics)_item_0_2
  • In 2002, Lydia Fairchild was denied public assistance in Washington state when DNA evidence appeared to show that she was not the mother of her children. A lawyer for the prosecution heard of a human chimera in New England, Karen Keegan, and suggested the possibility to the defense, who were able to show that Fairchild, too, was a chimera with two sets of DNA, and that one of those sets could have been the mother of the children.Chimera (genetics)_item_0_3
  • In 2002, an article in the New England Journal of Medicine describes a woman in whom tetragametic chimerism was unexpectedly identified after undergoing preparations for kidney transplant that required the patient and her immediate family to undergo histocompatibility testing, the result of which suggested that she was not the biologic mother of two of her three children.Chimera (genetics)_item_0_4
  • In 2009, singer Taylor Muhl discovered that what was always thought to be a large birthmark on her torso was actually caused by chimerism.Chimera (genetics)_item_0_5
  • In 2017, a human-pig chimera was reported to have been created; the chimera was also reported to have 0.001% human cells, with the balance being pig.Chimera (genetics)_item_0_6

Hermaphrodites Chimera (genetics)_section_7

Chimera (genetics)_unordered_list_1

  • Debate exists surrounding true hermaphrodites in regards to a hypothetical scenario in which it could be possible for a human to self-fertilize. If a human chimera is formed from a male and female zygote fusing into a single embryo, giving an individual functional gonadal tissue of both types, such a self-fertilization is feasible. Indeed, it is known to occur in non-human species where hermaphroditic animals are common. However, no such case of functional self-fertilization has ever been documented in humans.Chimera (genetics)_item_1_7

Bone marrow recipients Chimera (genetics)_section_8

Chimera (genetics)_unordered_list_2

  • Several cases of unusual chimera phenomena have been reported in bone marrow recipients.Chimera (genetics)_item_2_8
    • In 2019, the blood and seminal fluid of a man in Reno, Nevada (who had undergone a vasectomy), exhibited only the genetic content of his bone marrow donor. Swabs from his lips, cheek and tongue showed mixed DNA content.Chimera (genetics)_item_2_9
    • The DNA content of semen from an assault case in 2004 matched that of a man who had been in prison at the time of the assault, but who had been a bone marrow donor for his brother, who was later determined to have committed the crime.Chimera (genetics)_item_2_10
    • In 2008, A man was killed in a traffic accident that occurred in Seoul, South Korea. In order to identify him, his DNA was analyzed. Results revealed that the DNA of his blood, along with some of his organs, appeared to show that he was female. It was later determined that he had received a bone marrow transplant from his daughter.Chimera (genetics)_item_2_11

Chimera Identification Chimera (genetics)_section_9

Chimerism is so rare, that there have only been 100 confirmed cases in humans. Chimera (genetics)_sentence_74

However, this may be due to the fact that humans might not be aware that they have this condition to begin with. Chimera (genetics)_sentence_75

There are usually no signs or symptoms for chimerism other than a few physical symptoms such as hyper-pigmentation, hypo-pigmentation, or possessing two different colored eyes. Chimera (genetics)_sentence_76

However, these signs do not necessarily mean an individual is a chimera and should only be seen as possible symptoms. Chimera (genetics)_sentence_77

Again, forensic investigation or curiosity over a failed maternity/paternity DNA test usually leads to the accidental discovery of this condition. Chimera (genetics)_sentence_78

By simply undergoing a DNA test, which usually consists of either a swift cheek swab or a blood test, the discovery of the once unknown second genome is made, therefore identifying that individual as a chimera. Chimera (genetics)_sentence_79

Research Chimera (genetics)_section_10

The first known primate chimeras are the rhesus monkey twins, Roku and Hex, each having six genomes. Chimera (genetics)_sentence_80

They were created by mixing cells from totipotent four cell blastocysts; although the cells never fused, they worked together to form organs. Chimera (genetics)_sentence_81

It was discovered that one of these primates, Roku, was a sexual chimera; as four percent of Roku's blood cells contained two x chromosomes. Chimera (genetics)_sentence_82

A major milestone in chimera experimentation occurred in 1984 when a chimeric sheep–goat was produced by combining embryos from a goat and a sheep, and survived to adulthood. Chimera (genetics)_sentence_83

In August 2003, researchers at the Shanghai Second Medical University in China reported that they had successfully fused human skin cells and rabbit ova to create the first human chimeric embryos. Chimera (genetics)_sentence_84

The embryos were allowed to develop for several days in a laboratory setting, and then destroyed to harvest the resulting stem cells. Chimera (genetics)_sentence_85

In 2007, scientists at the University of Nevada School of Medicine created a sheep whose blood contained 15% human cells and 85% sheep cells. Chimera (genetics)_sentence_86

On January 22, 2019 the released an article — Chimerism Explained: How One Person Can Unknowingly Have Two Sets of DNA, where they state “Tetragametic Chimerism, where a twin pregnancy evolves into one child, is currently believed to be one of the rarer forms. Chimera (genetics)_sentence_87

However, we know that 20 to 30 percent of singleton pregnancies were originally a twin or a multiple pregnancy. Chimera (genetics)_sentence_88

Due to this statistic, it is quite possible that tetragametic chimerism is more common than current data implies”. Chimera (genetics)_sentence_89

Sponges Chimera (genetics)_section_11

Chimerism has been found in some species of marine sponges. Chimera (genetics)_sentence_90

Four distinct genotypes have been found in a single individual, and there is potential for even greater genetic heterogeneity. Chimera (genetics)_sentence_91

Each genotype functions independently in terms of reproduction, but the different intra-organism genotypes behave as a single large individual in terms of ecological responses like growth. Chimera (genetics)_sentence_92

Mice Chimera (genetics)_section_12

Chimeric mice are important animals in biological research, as they allow for the investigation of a variety of biological questions in an animal that has two distinct genetic pools within it. Chimera (genetics)_sentence_93

These include insights into problems such as the tissue specific requirements of a gene, cell lineage, and cell potential. Chimera (genetics)_sentence_94

The general methods for creating chimeric mice can be summarized either by injection or aggregation of embryonic cells from different origins. Chimera (genetics)_sentence_95

The first chimeric mouse was made by Beatrice Mintz in the 1960s through the aggregation of eight-cell-stage embryos. Chimera (genetics)_sentence_96

Injection on the other hand was pioneered by Richard Gardner and Ralph Brinster who injected cells into blastocysts to create chimeric mice with germ lines fully derived from injected embryonic stem cells (ES cells). Chimera (genetics)_sentence_97

Chimeras can be derived from mouse embryos that have not yet implanted in the uterus as well as from implanted embryos. Chimera (genetics)_sentence_98

ES cells from the inner cell mass of an implanted blastocyst can contribute to all cell lineages of a mouse including the germ line. Chimera (genetics)_sentence_99

ES cells are a useful tool in chimeras because genes can be mutated in them through the use of homologous recombination, thus allowing gene targeting. Chimera (genetics)_sentence_100

Since this discovery occurred in 1988, ES cells have become a key tool in the generation of specific chimeric mice. Chimera (genetics)_sentence_101

Underlying biology Chimera (genetics)_section_13

The ability to make mouse chimeras comes from an understanding of early mouse development. Chimera (genetics)_sentence_102

Between the stages of fertilization of the egg and the implantation of a blastocyst into the uterus, different parts of the mouse embryo retain the ability to give rise to a variety of cell lineages. Chimera (genetics)_sentence_103

Once the embryo has reached the blastocyst stage, it is composed of several parts, mainly the trophectoderm, the inner cell mass, and the primitive endoderm. Chimera (genetics)_sentence_104

Each of these parts of the blastocyst gives rise to different parts of the embryo; the inner cell mass gives rise to the embryo proper, while the trophectoderm and primitive endoderm give rise to extra embryonic structures that support growth of the embryo. Chimera (genetics)_sentence_105

Two- to eight-cell-stage embryos are competent for making chimeras, since at these stages of development, the cells in the embryos are not yet committed to give rise to any particular cell lineage, and could give rise to the inner cell mass or the trophectoderm. Chimera (genetics)_sentence_106

In the case where two diploid eight-cell-stage embryos are used to make a chimera, chimerism can be later found in the epiblast, primitive endoderm, and trophectoderm of the mouse blastocyst. Chimera (genetics)_sentence_107

It is possible to dissect the embryo at other stages so as to accordingly give rise to one lineage of cells from an embryo selectively and not the other. Chimera (genetics)_sentence_108

For example, subsets of blastomeres can be used to give rise to chimera with specified cell lineage from one embryo. Chimera (genetics)_sentence_109

The Inner Cell Mass of a diploid blastocyst, for example, can be used to make a chimera with another blastocyst of eight-cell diploid embryo; the cells taken from the inner cell mass will give rise to the primitive endoderm and to the epiblast in the chimera mouse. Chimera (genetics)_sentence_110

From this knowledge, ES cell contributions to chimeras have been developed. Chimera (genetics)_sentence_111

ES cells can be used in combination with eight-cell-and two-cell-stage embryos to make chimeras and exclusively give rise to the embryo proper. Chimera (genetics)_sentence_112

Embryos that are to be used in chimeras can be further genetically altered in order to specifically contribute to only one part of chimera. Chimera (genetics)_sentence_113

An example is the chimera built off of ES cells and tetraploid embryos, which are artificially made by electrofusion of two two-cell diploid embryos. Chimera (genetics)_sentence_114

The tetraploid embryo will exclusively give rise to the trophectoderm and primitive endoderm in the chimera. Chimera (genetics)_sentence_115

Methods of production Chimera (genetics)_section_14

There are a variety of combinations that can give rise to a successful chimera mouse and – according to the goal of the experiment – an appropriate cell and embryo combination can be picked; they are generally but not limited to diploid embryo and ES cells, diploid embryo and diploid embryo, ES cell and tetraploid embryo, diploid embryo and tetraploid embryo, ES cells and ES cells. Chimera (genetics)_sentence_116

The combination of embryonic stem cell and diploid embryo is a common technique used for the making of chimeric mice, since gene targeting can be done in the embryonic stem cell. Chimera (genetics)_sentence_117

These kinds of chimeras can be made through either aggregation of stem cells and the diploid embryo or injection of the stem cells into the diploid embryo. Chimera (genetics)_sentence_118

If embryonic stem cells are to be used for gene targeting to make a chimera, the following procedure is common: a construct for homologous recombination for the gene targeted will be introduced into cultured mouse embryonic stem cells from the donor mouse, by way of electroporation; cells positive for the recombination event will have antibiotic resistance, provided by the insertion cassette used in the gene targeting; and be able to be positively selected for. Chimera (genetics)_sentence_119

ES cells with the correct targeted gene are then injected into a diploid host mouse blastocyst. Chimera (genetics)_sentence_120

Then, these injected blastocysts are implanted into a pseudo pregnant female surrogate mouse, which will bring the embryos to term and give birth to a mouse whose germline is derived from the donor mouse's ES cells. Chimera (genetics)_sentence_121

This same procedure can be achieved through aggregation of ES cells and diploid embryos, diploid embryos are cultured in aggregation plates in wells where single embryos can fit, to these wells ES cells are added the aggregates are cultured until a single embryo is formed and has progressed to the blastocyst stage, and can then be transferred to the surrogate mouse. Chimera (genetics)_sentence_122

Plants Chimera (genetics)_section_15

Structure Chimera (genetics)_section_16

The distinction between sectorial, mericlinal and periclinal plant chimeras are widely used. Chimera (genetics)_sentence_123

Graft chimeras Chimera (genetics)_section_17

Main article: Graft-chimaera Chimera (genetics)_sentence_124

These are produced by grafting genetically different parents, different cultivars or different species (which may belong to different genera). Chimera (genetics)_sentence_125

The tissues may be partially fused together following grafting to form a single growing organism that preserves both types of tissue in a single shoot. Chimera (genetics)_sentence_126

Just as the constituent species are likely to differ in a wide range of features, so the behavior of their periclinal chimeras is like to be highly variable. Chimera (genetics)_sentence_127

The first such known chimera was probably the Bizzaria, which is a fusion of the Florentine citron and the sour orange. Chimera (genetics)_sentence_128

Well-known examples of a graft-chimera are Laburnocytisus 'Adamii', caused by a fusion of a Laburnum and a broom, and "Family" trees, where multiple varieties of apple or pear are grafted onto the same tree. Chimera (genetics)_sentence_129

Many fruit trees are cultivated by grafting the body of a sapling onto a rootstock. Chimera (genetics)_sentence_130

Chromosomal chimeras Chimera (genetics)_section_18

These are chimeras in which the layers differ in their chromosome constitution. Chimera (genetics)_sentence_131

Occasionally, chimeras arise from loss or gain of individual chromosomes or chromosome fragments owing to misdivision. Chimera (genetics)_sentence_132

More commonly cytochimeras have simple multiple of the normal chromosome complement in the changed layer. Chimera (genetics)_sentence_133

There are various effects on cell size and growth characteristics. Chimera (genetics)_sentence_134

Nuclear gene-differential chimeras Chimera (genetics)_section_19

These chimeras arise by spontaneous or induced mutation of a nuclear gene to a dominant or recessive allele. Chimera (genetics)_sentence_135

As a rule, one character is affected at a time in the leaf, flower, fruit, or other parts. Chimera (genetics)_sentence_136

Plastid gene-differential chimeras Chimera (genetics)_section_20

These chimeras arise by spontaneous or induced mutation of a plastid gene, followed by the sorting-out of two kinds of plastid during vegetative growth. Chimera (genetics)_sentence_137

Alternatively, after selfing or nucleic acid thermodynamics, plastids may sort-out from a mixed egg or mixed zygote respectively. Chimera (genetics)_sentence_138

This type of chimera is recognized at the time of origin by the sorting-out pattern in the leaves. Chimera (genetics)_sentence_139

After sorting-out is complete, periclinal chimeras are distinguished from similar looking nuclear gene-differential chimeras by their non-mendelian inheritance. Chimera (genetics)_sentence_140

The majority of variegated-leaf chimeras are of this kind. Chimera (genetics)_sentence_141

All plastid gene- and some nuclear gene-differential chimeras affect the color of the plasmids within the leaves, and these are grouped together as chlorophyll chimeras, or preferably as variegated leaf chimeras. Chimera (genetics)_sentence_142

For most variegation, the mutation involved is the loss of the chloroplasts in the mutated tissue, so that part of the plant tissue has no green pigment and no photosynthetic ability. Chimera (genetics)_sentence_143

This mutated tissue is unable to survive on its own, but it is kept alive by its partnership with normal photosynthetic tissue. Chimera (genetics)_sentence_144

Sometimes chimeras are also found with layers differing in respect of both their nuclear and their plastid genes. Chimera (genetics)_sentence_145

Origins Chimera (genetics)_section_21

There are multiple reasons to explain the occurrence of plant chimera during plant recovery stage: Chimera (genetics)_sentence_146

(1) The process of shoot organogenesis starts form the multicellular origin. Chimera (genetics)_sentence_147

(2) The endogenous tolerance leads to the ineffectiveness of the weak selective agents. Chimera (genetics)_sentence_148

(3) A self-protection mechanism (cross protection). Chimera (genetics)_sentence_149

Transformed cells serve as guards to protect the untransformed ones. Chimera (genetics)_sentence_150

(4) The observable characteristic of transgenic cells may be a transient expression of the marker gene. Chimera (genetics)_sentence_151

Or it may due to the presence of agrobacterium cells. Chimera (genetics)_sentence_152

Detection Chimera (genetics)_section_22

Untransformed cells should be easy to detect and remove to avoid chimeras. Chimera (genetics)_sentence_153

This is because it is important to maintain the stable ability of the transgenic plants across different generations. Chimera (genetics)_sentence_154

Reporter genes such as GUS and Green Fluorescent Protein (GFP) are utilized in combination with plant selective markers (herbicide, antibody etc.) However, GUS expression depends on the plant development stage and GFP may be influenced by the green tissue autofluorescence. Chimera (genetics)_sentence_155

Quantitative PCR could be an alternative method for chimera detection. Chimera (genetics)_sentence_156

Viruses Chimera (genetics)_section_23

In 2012, the first example of an RNA-DNA hybrid virus was unexpectedly discovered during a metagenomic study of the acidic extreme environment of Boiling Springs Lake that is in Lassen Volcanic National Park, California. Chimera (genetics)_sentence_157

The virus was named BSL-RDHV (Boiling Spring Lake RNA DNA Hybrid Virus). Chimera (genetics)_sentence_158

Its genome is related to a DNA circovirus, which usually infect birds and pigs, and a RNA tombusvirus, which infect plants. Chimera (genetics)_sentence_159

The study surprised scientists, because DNA and RNA viruses vary and the way the chimera came together was not understood. Chimera (genetics)_sentence_160

Other viral chimeras have also been found, and the group is known as the CHIV viruses ("chimeric viruses"). Chimera (genetics)_sentence_161

Ethics and legislation Chimera (genetics)_section_24

See also: Bioethics Chimera (genetics)_sentence_162

Ethics Chimera (genetics)_section_25

The US and Western Europe have strict codes of ethics and regulations in place that expressly forbid certain subsets of experimentation using human cells, though there is a vast difference in the regulatory framework. Chimera (genetics)_sentence_163

Through the creation of human chimeras comes the question: where does society now draw the line of humanity? Chimera (genetics)_sentence_164

This question poses serious legal and moral issues, along with creating controversy. Chimera (genetics)_sentence_165

Chimpanzees, for example, are not offered any legal standing, and are put down if they pose a threat to humans. Chimera (genetics)_sentence_166

If a chimpanzee is genetically altered to be more similar to a human, it may blur the ethical line between animal and human. Chimera (genetics)_sentence_167

Legal debate would be the next step in the process to determine whether certain chimeras should be granted legal rights. Chimera (genetics)_sentence_168

Along with issues regarding the rights of chimeras, individuals have expressed concern about whether or not creating human chimeras diminishes the dignity of being human. Chimera (genetics)_sentence_169

Legislation Chimera (genetics)_section_26

The Human Chimera Prohibition Act Chimera (genetics)_section_27

On 11 July 2005, a bill known as The Human Chimera Prohibition Act, was introduced into the United States Congress by Senator Samuel Brownback; however, it died in Congress sometime in the next year. Chimera (genetics)_sentence_170

The bill was introduced based on the findings that science has progressed to the point where the human and nonhuman species can be merged to create new forms of life. Chimera (genetics)_sentence_171

Because of this, serious ethical issues arise as this blurs the line between humans and other animals, and according to the bill with this blurring of the lines comes a show of disrespect for human dignity. Chimera (genetics)_sentence_172

The final claim brought up in The Human Chimera Prohibition Act was that there is an increasing amount of zoonotic diseases. Chimera (genetics)_sentence_173

With that being said, the creation of human-animal chimeras can allow these diseases to reach humans. Chimera (genetics)_sentence_174

On 22 August 2016, another bill, The Human-Animal Chimera Prohibition Act of 2016, was introduced to the United States House of Representatives. Chimera (genetics)_sentence_175

It identifies a chimera as: Chimera (genetics)_sentence_176

Chimera (genetics)_unordered_list_3

  • a human embryo into which a nonhuman cell or cells (or the component parts thereof) have been introduced to render the embryo's membership in the species Homo sapiens uncertain;Chimera (genetics)_item_3_12
  • a chimera human/animal embryo produced by fertilizing a human egg with nonhuman sperm;Chimera (genetics)_item_3_13
  • chimera human/animal embryo produced by fertilizing a nonhuman egg with human sperm;Chimera (genetics)_item_3_14
  • an embryo produced by introducing a nonhuman nucleus into a human egg;Chimera (genetics)_item_3_15
  • an embryo produced by introducing a human nucleus into a nonhuman egg;Chimera (genetics)_item_3_16
  • an embryo containing at least haploid sets of chromosomes from both a human and a nonhuman life form;Chimera (genetics)_item_3_17
  • a nonhuman life form engineered such that human gametes develop within the body of a nonhuman life form; orChimera (genetics)_item_3_18
  • a nonhuman life form engineered such that it contains a human brain or a brain derived wholly or predominantly from human neural tissues.Chimera (genetics)_item_3_19

The bill prohibits the attempts to create a human-animal chimera, the transfer or attempt to transfer a human embryo into a nonhuman womb, the transfer or attempt to transfer a nonhuman embryo into a human womb, and the transport or receive of any purpose of an animal chimera. Chimera (genetics)_sentence_177

Penalties for violations of this bill include fines and/or imprisonment of up to 10 years. Chimera (genetics)_sentence_178

The bill was referred to the Subcommittee on Crime, Terrorism, Homeland Security, and Investigations in October 11, 2016, but died there. Chimera (genetics)_sentence_179

See also Chimera (genetics)_section_28

Chimera (genetics)_unordered_list_4

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: (genetics).