question: Would twin yolks (chicken, etc) hatch into 2 chicks like human twins?
comment: The yolk doesn't become the embryo. The little white nodule that's in the egg and attached to the yolk becomes the embryo. The yolk is nutrients to keep the embryo alive until the egg hatches.
passages: Double-yolk eggs occur when ovulation occurs too rapidly, or when one yolk becomes joined with another yolk. These eggs may be the result of a young hen's reproductive cycle not yet being synchronized.
  
  Double-yolked eggs seldom lead to successful hatchlings without human intervention, as the chicks interfere with each other's hatching process and do not survive.
  
  Higher-order yolks are rare, although heavier poultry breeds such as the Buff Orpington have been known to lay triple-yolk eggs occasionally.
  
  Section::::Chicken egg yolk.:Yolkless eggs.
   Since these eggs contain no yolk, so cannot hatch, they were traditionally believed to have been laid by roosters. This type of egg occurs in many varieties of fowl and has been found in chickens, both standard and bantams, guineas, and coturnix quail.
  
  Section::::Chicken egg yolk.:Yolk color.
   Parthenogenesis in birds is known mainly from studies of domesticated turkeys and chickens, although it has also been noted in the domestic pigeon. In most cases the egg fails to develop normally or completely to hatching. The first description of parthenogenetic development in a passerine was demonstrated in captive zebra finches, although the dividing cells exhibited irregular nuclei and the eggs did not hatch.
   When fast normal-feathering "k""k" cocks are mated to delayed-feathering "K" hens, the sex of all the descendants can be easily recognized at hatch: resulting female chicks "k" have fast normal-feathering (see Figure 2A) while male chicks "Kk" have delayed-feathering (see Figure 2B and 2C).
  
  This happens because female birds have a single Z sexual chromosome, while males carry two, contrarily to what happens in humans, where the male is the heterogametic sex, as occurs in most diploid species.
   Eggs without yolks are known as "dwarf" or "wind" eggs, or the archaic term "cock egg". Such an egg is most often a pullet's first effort, produced before her laying mechanism is fully ready. Mature hens rarely lay a yolkless egg, but sometimes a piece of reproductive tissue breaks away and passes down the tube. Such a scrap of tissue may stimulate the egg-producing glands to react as though it were a yolk and wrap it in albumen, membranes, and a shell as it travels through the egg tube. This is usually what causes an egg to contain a small particle of grayish tissue instead of a yolk.
   BULLET::::6. Failure to incorporate the yolk sac and related vitelline structures into the yolk sac
   "K" is another dominant allele of the allelic series which controls feather growth rate. One-day-old chicks have primary remiges and coverlets of the same length (see Figure 2B). In 8- to 12-day-old chicks rectrices are not yet developed (see Figure 1, chick on the right).
  
  Feather growth rate is generally slower in "K"-carriers than in fast normal-feathering birds. But this allele has not any effect on adult plumage. Sex-linked delayed-feathering is typical in many meat-type breeds.
  
  Section::::Sex-linked feathering.:"k" (fast normal-feathering).
   Occasionally, the birds form same-sex pairs consisting of two females. This has been observed in the colony on the Hawaiian island Oahu, where the sex ratio of male to female is 2 to 3 and 31% of all pairs are between females. Paired females can successfully breed when their eggs are fertilized by males. This phenomenon has been useful to conservation efforts in the Hawaiian Islands, where researchers have successfully swapped unfertilized eggs from female-female pairs with fertile eggs translocated from pairs nesting on military airfields and in other unsafe nesting areas. The female-female pairs then hatch and raise the foster chicks.
   "k" carrier females are always of the fast normal-feathering type, while heterozygous "Kk" males are of the delayed-feathering type because of the dominance of "K" over "k".
  
  This regularity found practical use in commercial poultry breeding to separate chicks of different sexes in the hatcheries, thus avoiding the inconveniences associated with vent sexing and making easier, faster, harmless and cheaper the sex identification in one-day-old chicks.
   The larger yolk content of the mesolecithal eggs allows for a longer fetal development. Comparatively anatomically simple animals will be able to go through the full development and leave the egg in a form reminiscent of the adult animal. This is the situation found in hagfish and some snails. Animals with smaller size eggs or more advanced anatomy will still have a distinct larval stage, though the larva will be basically similar to the adult animal, as in lampreys, coelacanth and the salamanders.
  
  Section::::Scientific classifications.:Egg size and yolk.:Macrolecithal.
   Section::::Autosomal "T" allelic series.
  
  Contrary to multifactorial slow-feathering genes, which affect only chicks carrying "K", the autosomal recessive alleles "t" ("tardy") and "t" ("retarded") of the "T" allelic series affect only those chicks of the fast normal-feathering type. The dominance order is "T" (normal)  "t" ("retarded")  "t" ("tardy").
  
  Section::::Autosomal "T" allelic series.:"Retarded" "t""t" chicks.
  
  Fast normal-feathering one-day-old chicks have six primary remiges and at least another six secondary remiges (see Figure 3A). While "retarded" "t""t" one-day-old chicks have normal primary remiges but only the first three (external) secondary remiges.
   Together with hatchling specimens of the Mongolian "Gobipteryx" and "Gobipipus", these finds demonstrate that enantiornithean hatchlings had the skeletal ossification, well-developed wing feathers, and large brain which correlate with precocial or superprecocial patterns of development in birds of today. In other words, enantiornitheans probably hatched from the egg already well developed and ready to run, forage, and possibly even fly at just a few days old.
   "k" is the most recessive of the allelic series. One-day-old chicks pure for this allele have the primary remiges evidently longer than the coverlets (see Figure 2A) while 8- to 12-day-old chicks show their rectrices well developed (see Figure 1, chick on the left), and they later complete feather growing long before those chicks carrying "K".
  
  "k" is responsible for the fast normal-feathering found in most egg-type breeds like Leghorn, Minorca, Ancona and many others.
  
  Section::::Sex-linked feathering.:Practical use of the sex-linked variation.
   Bird eggs are laid by females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about 17 (the grey partridge). Some birds lay eggs even when not fertilized (e.g. hens); it is not uncommon for pet owners to find their lone bird nesting on a clutch of unfertilized eggs, which are sometimes called wind-eggs.
  
  Section::::Eggs of different animal groups.:Bird eggs.:Colors.
   A study of Noy et al. (1996) showed that the residual yolk of chickens with access to feed during 96 hours after hatch reduced more rapid in size than in fasted birds. This can be caused by increased intestinal activity in fed chickens. A more rapid reduction in residual yolk size indicates that valuable nutrients are earlier used for important developmental steps.
   Japanese quail eggs have orbited the Earth in several Soviet and Russian spacecraft, including the Bion 5 satellite and the Salyut 6 and Mir space stations. In March 1990, eggs on Mir were successfully incubated and hatched.
  
  Section::::See also.
  
  BULLET::::- List of birds of Japan
  
  BULLET::::- Lists of Korean birds
  
  BULLET::::- Quails in cookery
  
  Section::::External links.
  
  BULLET::::- BirdLife Species Factsheet
  
  BULLET::::- Slovak Commission for Research and Peaceful Uses of Space, with details on Ivan Bella's quail experiments on Mir, including photo of zero-gravity chick
   Brood parasitism occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the cowbirds and many Old World cuckoos.
  
  Section::::Evolution.
   The sperm from a mating is stored by the female and can suffice to fertilise about six eggs. The pair mate every day or two, and every second or third day the female lays one of a clutch of five to fifteen very large, thick-shelled, green eggs. The shell is around thick, but rather thinner in northern regions according to indigenous Australians. The eggs are on average and weigh between . The maternal investment in the egg is considerable, and the proportion of yolk to albumen, at about 50%, is greater than would be predicted for a precocial egg of this size. This probably relates to the long incubation period which means the developing chick must consume greater resources before hatching. The first verified occurrence of genetically identical avian twins was demonstrated in the emu. The egg surface is granulated and pale green. During the incubation period, the egg turns dark green, although if the egg never hatches, it will turn white from the bleaching effect of the sun.
   The sex-linked slow-feathering gene can be used for crosses where the sex of the chicks can be determined at hatching time by the length of the wing feathers. A cross between a fast-feathering male and a slow-feathering female results in offspring where the female chicks have primary wing feathers that are significantly longer than the coverts. The male chicks have primary wing feathers that are shorter, about the same length as the coverts.
  
  Section::::Methods of chick sexing.:Colour sexing.
   Chicks of a single breed that are similarly sex-linked are called autosex chickens, a term developed to differentiate between sex linkage in purebred chickens versus sex linkage in crossbreeds.
  
  Section::::Sex-link types.
  
  Many common varieties are known as the black sex-link (also called black stars) and the red sex-link (also called red stars). More specific variety names are common as well.
   Then, a chase starts between Woody, Meany and her camel for who get the egg. Woody advises Meany to enter a metal door, which is locked by concrete. Meany crashes into it, breaking the egg in the process. Meanwhile, Woody steals one egg and runs away with it. Ms. Meany hang herself upsidedown and get the egg, without Woody notice. Once she climbs down the stair, Woody pecks out the blocks, while Ms. Meany tries her best for not falls. Woody takes a collumm of the stair, which difficult more. Woody uses a saw, and then Meany falls, breaking the egg once again.
   Chickens may occasionally gang up on a weak or inexperienced predator. At least one credible report exists of a young fox killed by hens.
  
  Section::::General biology and habitat.:Embryology.
  
  In 2006, scientists researching the ancestry of birds "turned on" a chicken recessive gene, "talpid2", and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils. John Fallon, the overseer of the project, stated that chickens have "...retained the ability to make teeth, under certain conditions... ."
  
  Section::::Breeding.
  
  Section::::Breeding.:Origins.
   Macrolecithal eggs go through a different type of development than other eggs. Due to the large size of the yolk, the cell division can not split up the yolk mass. The fetus instead develops as a plate-like structure on top of the yolk mass, and only envelopes it at a later stage. A portion of the yolk mass is still present as an external or semi-external yolk sac at hatching in many groups. This form of fetal development is common in bony fish, even though their eggs can be quite small. Despite their macrolecithal structure, the small size of the eggs does not allow for direct development, and the eggs hatch to a larval stage ("fry"). In terrestrial animals with macrolecithal eggs, the large volume to surface ratio necessitates structures to aid in transport of oxygen and carbon dioxide, and for storage of waste products so that the embryo does not suffocate or get poisoned from its own waste while inside the egg, see amniote.
   Some studies on crosses of chicken breeds point to the hypothesis of complementary genes acting on broodiness. Other results point to the hypothesis of sex-linked genes, or, inheritance through the maternal chromosome. Although these studies have been made on different breeds of chickens, their results are not contradictory. There is common agreement that artificial selection for egg production succeeded in reducing the incidence of broody hens in chicken populations.
  
  Section::::Broodiness in non-avian animals.
   Parthenogenesis in turkeys appears to result from a conversion of haploid cells to diploid; most embryos produced in this way die early in development. Rarely, viable birds result from this process, and the rate at which this occurs in turkeys can be increased by selective breeding, however male turkeys produced from parthenogenesis exhibit smaller testes and reduced fertility.
  
  Section::::Natural occurrence.:Mammals.
  
  There are no known cases of naturally occurring mammalian parthenogenesis in the wild. Parthenogenetic progeny of mammals would have two X chromosomes, and would therefore be female.
  
  In 1936, Gregory Goodwin Pincus reported successfully inducing parthenogenesis in a rabbit.
  
raw_presuppositions: Yolks in eggs are embryos.
raw_corrections: Yolks in eggs don't become the embryo.