Gemini is born not only in humans, but also in animals. Problem only that this topic has not been studied enough yet; based on assumptions than on real facts.
Content
- 1 Gemini: who they are
- 2 Among which animals are twins born
- 2.1 Are twins born in cats and dogs
Gemini: who they are
The mechanism of nucleation, intrauterine development and birth identical twins are the same in humans as in animals. Another thing is that so far the reasons why cells of one egg are divided in crushing and become independent embryos. It can happen as in the stage primary crushing, and much later – even when the embryo grows to several hundred cells.
Most often, the zygote is divided into autonomous embryos at the stage primary crushing
The bottom line is that two or more embryos originate from one egg (zygote), fertilized by one sperm. Hence the same-sex identity of the twins, and their stunning outward similarity, and behavioral coincidences, and that more importantly, deep internal similarity at the genotype level.
Is it possible to artificially, in laboratory conditions, get twins from one zygote? Yes, and scientists have repeatedly put such experiments. It is important not to miss the moment of primary crushing, so that carefully divide the egg into two halves and place them for development in a comfortable nutrient environment. Violent attempts zygote separation in later stages has not yet been successful crowned, although, we repeat, in nature such cases are not uncommon.
But the zygote may not separate completely. Not reliable statistics on how often this happens, but we all know examples of four-footed geese and six-legged calves, two-tailed fish and donkeys, a variety of animals with two heads. Such individuals are born precisely because of incomplete separation eggs to autonomous embryos. Many of them turn out to be quite viable: do not die soon after birth, but live to see full maturity. At all times, such animals were considered freaks, attracted increased attention, and sometimes cause people mystical horror.
A two-headed snake was discovered in Uzbekistan: length the reptile reached 30 cm, and the tongues in both mouths moved synchronously
Most likely, the two-headed eagle also had a real prototype, for the first time appeared on the coat of arms of Byzantium, and later migrated to the coat of arms Russian empire. And prototypes of mythical many-headed dragons, quite possibly, two- and three-headed reptiles (snakes, lizards, turtles): these animals have the most similar phenomena common.
Interestingly, approximately a quarter of monozygotic twins are mirror images of each other, external and internal copies “exactly the opposite.” Scientists believe that such mirror pairs are formed when the egg is not divided into primary, but at a later stage.
Among which animals are twins born
Gemini can be called natural clones, because from one zygotes can come out two, three or more independent individuals, sets genes which will be identical. Most often, such phenomena occur in organisms not of the highest level, but especially often in parasites, for which the conservation of the species in difficult conditions.
Riding insect parasites are amazingly powerful. to natural cloning. Females of these hymenopterans introduce their eggs into the larvae of other insects, on which they parasitize further. So, from one laid egg in some species riders could theoretically develop up to a half thousand the twins! Of course, in practice this never happens because lack of nutrients and other necessary conditions – but the potential, you see, is impressive.
If we talk about more highly organized animals, then here the situation is different. In birds, for example, cases the appearance, and even more so the survival of the twins are extremely rare, although observe the same chicken eggs with two yolks to each of them happened more than once. But only a few episodes are recorded, when two chickens hatched from one egg, they were very small they almost never managed to be saved even with the most thorough care. It is doubtful that in the wild weakened twin chicks are able to survive.
These wonderful parrots are not twins at all, but their similarities due to belonging to one species
Similar situations in fish, amphibians and reptiles are explained the fact that their embryos are limited in development opportunities nutritional supplies of eggs or eggs. And that’s enough for the growth of one germ, for two it will be completely insufficient. Underfed at the stage of embryonic development of an individual will be unequivocally eliminated in the process of hard natural selection. There are only chances of survival “half twins”: double-headed snakes and other freaks.
A completely different embryo develops in mammals – it receives nutrition through the placenta from the mother’s body, which gives twins are far more likely to be born. However, and everything is not too rosy here, even if we proceed from analogies with human pregnancy, which for obvious reasons investigated much better.
Biologists suggest that mammals are born only every eighth, or even every tenth of the possible twins – the rest disappear without a trace even in the early stages of pregnancy: either miscarriages or embryo absorption maternal organism, and sometimes the absorption of a single germ twin to other stronger.
You need to understand that in small species of mammals are common multiple pregnancies, and in larger ones, except for feline and canine predators are one-fruited. If in the first case it’s very difficult systematize the birth of twins, then in the second they are all but more visual. Most often, we can observe such examples in large ungulates – but here, too, without special research it is impossible argue that two cubs, for example, elephants are monozygotic twins, not twins.
Only genetic research can clarify who these elephants: twins or twins?
However, nature is a big lover toss us surprises and riddles. Regarding the topic of twins, here not to mention such stunning animals as armadillos. For these amazing in every way Hispanic mammals twin birth – not randomness, and regularity.
Polyembryony is characteristic of armadillos: in a female, before mating only one egg matures, which after fertilization divided into several embryos. The most famous the number of one offspring in these animals is twelve cubs: all of them are twins, and all, of course, are of only one gender.
Only twins can be born to a female armadillo
Do twins in cats and dogs
At the philistine level, substitution usually takes place concepts or some confusion about twin animals. On the Internet you can find a huge the number of cute photos with very similar animals that issued as twins. But definitely do not confuse identity on gene level with the banal coincidence of species or species signs.
Oddly enough, such misconceptions most often concern the most popular pets: cats and dogs. Both those and other pets multiple: for many dog breeds, for example, is not the rarity of giving birth to ten or more puppies in one litter. But you can Do all of them be considered twins? Of course not, even if the kids are very are similar to each other.
White-eyed sisters Iriss and Abyss live in St. Petersburg; the owners consider them twins, but the DNA test for some reason they don’t
Line breeding practitioners consider cubs “clones” with their luck, confirmation of the right one parental couple. But litter stability, manifested in the uniformity of the cub phenotype is not at all evidence that they are all twins. Reliable evidence of this fact only DNA analysis can become – it should show gene identity of twin littermates.
The first official confirmation of the appearance twin puppies were received in South Africa three years ago. Bitch Irish wolfhound could not be born herself, and had to do her cesarean section. During the operation, the veterinarian discovered two embryos whose umbilical cord was attached to one placenta.
The kids were safely born, and made them two weeks a DNA test confirmed the genetic identity of the brothers: they really were identical twins. If the bitch gave birth naturally, this fact would be impossible to establish. By more that just these two babies had some differences in color intensity. This is because twins may show different activity of the same genes.
In the study of the theme of twin animals, there are still many bright discoveries. Who knows, maybe they will help scientists re-evaluate many questions of the stunningly interesting science of genetics.
