Axolotls et cie, La génétique de notre axolotl

genetique

GENETIC

(at the bottom of the page)

Axolotl color is generated by three different types of cells which can cause various color mutations in their interaction.

• Melanophore:Cell that stores melanin which is a dark pigment (Melanos = black).

• Xanthophore:Xanthophores are yellow pigment cells; it is a yellowish chromatophore (Xanthos = yellow).

• Iridophore:An iridophore distinguishes a cell endowed with iridescence possibilities, like a chromatophore (Iridios = brilliant).All genes have two alleles. The alleles can be dominant or recessive or even intermediate.

Wild type: The wild type Axolotl contains all three types of pigment cells. The dark color is due to the melanophores. With the xanthophore gene it becomes ocher or dark green, its color may vary depending on the individual depending on the concentration of pigments. The shiny spots, especially in the tail and dorsal veil are caused by iridophores. The cooper is a wild one without black pigments. As the gene is dominant for the expression of all types of pigments, all axolotls have it in their phenotype. The most important range of color is found in the wild type which has all the genes (from yellow to purple to green to gray. 8-)

WILD

MELANICS

Melanistic axolotls can be white, gray, and black. In their skin the iridophores have not formed so the silvery sheen is removed. Their eyes are completely dark without irises and / or dull like with melanic albinos. The skin is also matte in color.

Black melanic

Albino melanic

Animals that do not produce melanophores or iridophores, homozygous with a slight tint of yellow by the xanthophore present in it.

AXANTHICS

Albino axanthic

They are white, but may have a slight metallic sheen. They lack melanophores and xanthophores, so only the iridophore remains present. So homozygous.

Axanthic gray

axanthique dalmatien, axolotl axanthique

Axanthic axolotls lack the xanthophore gene. However, they do not differ much from very dark wild types as the concentration of melanin can be very pronounced individually. This phenotype probably cannot be determined with certainty by backcrossing.

ALBINO

The first type of albino is the white albino. It is homozygous for "d" and "a" (d / d and a / a). Presence of iridophores (shiny pigment cells) in its gills. White albinos have very white skin and red eyes with red gills. NB: Many of our white albinos do not have iridophores so they are in fact axantic albinos. Which will turn a little yellow over the years. The second type of albino is the axanthic albino. It has normal pigment cell migration, but is homozygous for the albino gene and the axanthic gene (a / a and ax / ax), which means it lacks the melanophores, xanthophores and iridophores. It is almost matte white, but turns yellow with age due to the buildup of riboflavins in its diet. The third type is the melanistic albino. It is homozygous for "m" and "a" (m / ma / a). While a non-albino melanist would be black, the combination of melanism and albinism "removes" all pigments except a tiny hint of yellow xanthophores on the head and back. The fourth type of albino is the golden albino, the gold: The Phenotype is albino A / A (missing melanophores). There are several different types of albino axolotl phenotype. Here are a few of them. albino gold (D / D a / a or D / da / a). It has undergone normal migration of its pigment cells, but lacks melanophores, hence the appearance of yellow / gold. Gold Albinos are golden yellow with yellow eyes and red gills. The dark pigment of melanophores is missing, the characteristics of other pigments are normal. Homozygous for one, can be homo or heterozygous for the remaining genes. This color variation was made possible by a cross with the tiger salamander in the lineage of the axolotl, since no Axolotl was known to lack melanophores. This sort of color is also known as "Humphrey Axolotl" (name of the scientist who first created this cross).

GOLD

WHITE ALBINOS

LEUCISTIC

To make matters even more confusing, there is another characteristic that has nothing to do with the presence of pigments. Harlequin: the pigments disperse in the skin, but a fourth gene is active, called D. Is it defective? Or is there an incomplete distribution of pigments? In any case all the pigment cells, such as xanthophores, Iridophores or melanophores remain along the anterior neural crest of the embryo, where they were formed and do not migrate to other regions of the body as usual. It has a white body, but dark eyes and is very often pigmented on the back or on the head ("freckles"). With special shapes, the harlequin has strong pigmentation on the head and gills. Summary : Axolotls undergo a lot of color variation Breeders often produce singular offspring whose phenotype defies the genotype of the animal. The axolotls "pie" (and not only on the upper body like a leucistic), the yellow leucistic with black spots, there is also the harlequin with orange and black patches on the body are just a few examples of what chance can present.

But in view of the DNA of axolotl all colors are possible in the offspring as long as there have been crosses. So we will see new colors coming.

Scientific genetic aspect (more complex part):
The color of axolotl depends on pigment cells called chromatophores. These cells are melanophores (containing melanin, a brown-black pigment), xanthophores (containing yellow and red carotenoids, pigments and pteridins) and iridophores (containing Crystalised purines, which impart a brilliant iridescence).
Each axolotl cell, as shown above, contains 14 pairs of chromosomes. Each characteristic of animals is encoded by genes on pairs of chromosomes. Genes for pigment cells are inherited independently of each other, and there is no known link to other genes. Thus, each type of pigment is encoded by two different genes, one on each of the pairs of chromosomes. These contrasting genes which code for the same characteristic are known as alleles. A pair of alleles is written like this: X / x. An uppercase letter means the gene is a dominant gene, as opposed to a lowercase letter, which means the gene is recessive.
For example, the allele that controls albinism could be found in an axolotl in one of the following combinations: A / A, A / A, or A / A. If the animal was A / a, because a is recessive and A is dominant, the animal's phenotype would not be albino, but it would carry the albinism gene (because it has an "a"). Since it carries both "A" and "a", it is known as "heterozygous". If the animal had the A / A combination, its phenotype would not be albino, and it would not carry the albinism gene (the two genes being the same, it is called "homozygous" for "A") . If it were homozygous for "a" (that is -a / a), the animal's phenotype would be albino. Since "a" is recessive, both alleles must be "a" for albinism to be expressed in the phenotype. Results of albinism: a lack of melanin (the dark pigment). In axolotls, it also causes an increase in the number of xanthophores (yellow pigment cells).
In the same way that A / led to a lack of melanin, m / m (melanoid) results in a lack of iridophores. These animals are very dark, with no reflection (light) pigment cells. M / m or M / M would result in the development of iridophores normally. Animals homozygous for "ax" (ie ax / AX) are axanthic, meaning that they have no visible xanthophores or iridophores. These animals are almost as dark as the melanic ones. Animals homozygous for both albino and axanthic gene appear to be slightly off-white (yellowish). The following table summarizes the color genes

With a few exceptions, fertilization of urodeles is internal: the spermatozoa, contained in a spermatophore deposited by the male, are seized by the cloacal lips of the female. When hatching, the larvae attach themselves temporarily using "pendulums" whose ends produce an adhesive secretion. They have dorsal and caudal swimming ridges and special dentition. They breathe by means of three branchial tufts. The forelimbs develop before the hindquarters. Elimination of metamorphosis can be achieved by direct development which suppresses the aquatic free larval phase or by neotenia which eliminates the terrestrial phase.

The aquatic larval phase is thus completely suppressed in Salamandra atra, which is viviparous. An egg hatches in each oviduct as a larva with pendulums, lateral line organs and gills. The larva first feeds on the yolk of neighboring aborted eggs, then it connects with the wall of the oviduct through the external gills and is released at the end of its development.

In neotenic species, metamorphosis usually does not occur: larval characters persist throughout life, as well as the aquatic way of life. Neotenia is a specific trait that is almost definitively fixed in the classic case of axolotl, which only very rarely undergoes metamorphosis in its natural habitat. Thyroid treatment makes it possible to obtain metamorphosed individuals, because axolotl is only the neotenic larva of Ambystoma tigrinum. The causes of this facultative neotenia are poorly understood: quantitative insufficiency of thyroid secretion or poor tissue reactivity?

CONSANGUINITY

"In all the sexual species, that is to say all the species which mix the genetic capital of the male and the female to give an original individual, consanguinity increases the risk of seeing the appearance of so-called recessive genetic diseases (cystic fibrosis in man for example).
A recessive gene is a gene that does not express itself when it is present on only one out of two chromosomes. If it is present on both, the disease is expressed. Inbreeding increases the risk of seeing this gene present on the chromosomes provided by the mother and the father.
On the other hand, a priori, consanguinity does not make children more fragile or weaker if there is no specific genetic disease associated. There are many animal breeds from a very small number of initial parents and which do not suffer from this inbreeding (which must be distinguished from the defects selected precisely to create the breed in question). As a classic example, the English Thoroughbred breed in horses originated from three original males.
If one could prove that such a species does not present any recessive genetic disease (difficult to prove), inbreeding would not pose any problem to this species.
To my knowledge, in axolotl, no genetic disease has been demonstrated. Which doesn't mean there isn't ...
When in doubt in humans, many states prohibit marriages between first cousins. The practice is common in many other places.
When in doubt, in breeding, we try to avoid things that are too "shady" such as crosses between parents and young, brothers and sisters.

Dr Larroquette (Castres Tarn veterinary clinic)

In addition to this, you will need to know more about it.

To summarize: reproduction, for example between amphibian siblings, can on beautiful and strong strains (for this you need to know the genetic heritage) give beautiful babies carrying the best of both, or reinforce a genetic disorder. So before playing the sorcerer's apprentice it is absolutely necessary to know the genetic heritage of his axolotls, or other urodeles and to keep only the strongest and healthy ones. When in doubt, refrain ...

The Urodeles are represented by the current Amphibians which, in the adult state, typically have two pairs of motor limbs and a tail: thus newts, salamanders. Their lacertiform body is easily distinguished from that of lizards by bare skin, always devoid of scales. The front and back legs are roughly the same size. Their role in swimming is weak. On land, urodeles walk awkwardly with lateral body waves. When the development of the egg is complete, the majority of urodeles go through a free aquatic stage during which the animal moves and feeds. During this larval life, practically simultaneous processes of growth and regression take place which constitute metamorphosis.

We must insist on the important role of urodeles in experimental research: it is on the newt egg that H. Spemann demonstrated the phenomenon of induction; it is on this same germ that the experiments of separation of the first two blastomeres, of androgenesis or development controlled by the spermatic nucleus alone, and of increase in the number of chromosomal stocks (artificial polyploidy) by the thermal shock action. We must also mention the use of Urodeles larvae to carry out Siamese grafts, or parabiosis, to create intergeneric chimeras (Houillon's triton-axolotl chimeras), to operate complete and definitive transformations of the sex (as did Humphrey in axolotl and Gallienus in pleurodel).

Anatomy

Skeleton

The skull of urodeles is broadly similar to that of anurans . However, the frontal and parietal bones remain separate, the palatines are absent or united with the vomers, and the maxillae may be missing. The vertebrae are amphicoels or opisthocoels. They are characterized by the presence of long rib supports, often double.

(Source Universalis)