Turkeys are one of the few bird species confirmed to produce offspring without any contribution from a male. Unfertilized eggs laid by virgin turkey hens can, on rare occasions, begin developing embryos entirely on their own, a phenomenon called facultative parthenogenesis. The resulting embryos are almost always male, and while most die during development, a small number have hatched and even grown to adulthood. The phenomenon is not a quirk of captive breeding or laboratory manipulation; it is a genuine biological capability encoded in the turkey genome, and researchers have been studying it for over seventy years.
When Scientists First Noticed
The discovery dates to the early 1950s, when researchers at the USDA’s Beltsville Agricultural Research Center in Maryland observed that eggs from virgin Beltsville Small White turkey hens were showing signs of embryonic development despite never having contact with a male. The initial report was published in Science in 1952, and it prompted decades of follow-up work.1Science. Natural parthenogenesis in turkey eggs At the time, parthenogenesis was well known in insects and some reptiles, but finding it in a warm-blooded, commercially important bird was unexpected. Most of the early research was led by M.W. Olsen and colleagues at Beltsville, who spent years cataloguing rates of development, incubating thousands of unfertilized eggs, and eventually producing live poults from those eggs.
What Happens Inside the Egg
In normal sexual reproduction, a hen’s egg cell goes through two rounds of cell division (meiosis) to become a haploid ovum with half the usual number of chromosomes. Fertilization by a sperm cell restores the full chromosome count. In parthenogenesis, no sperm arrives, yet the egg begins dividing anyway. The critical question is how the embryo gets back to a full set of chromosomes without a father’s contribution.
Studies of early-stage turkey parthenotes show that the process starts in a haploid cell. The initial blastoderms, the tiny disc of dividing cells on top of the yolk, are typically mosaics of haploid, diploid, and polyploid cells.2PubMed Central. The Chromosomes of Turkey Embryos during Early Stages of Parthenogenetic Development As development continues, the proportion of haploid cells drops rapidly while the proportion of diploid cells rises. By around six days of incubation, surviving embryos are either fully diploid or a mosaic that is mostly diploid. The leading explanation is that the egg restores the full chromosome count either by suppressing the second round of meiosis or by doubling its chromosomes shortly after the first cell division.2PubMed Central. The Chromosomes of Turkey Embryos during Early Stages of Parthenogenetic Development Either way, the embryo ends up with two copies of the mother’s genetic material rather than one copy from each parent. This type of parthenogenesis is called automictic because it involves the egg’s own meiotic products recombining, as opposed to apomictic parthenogenesis where meiosis is skipped entirely.
A separate study tracking chromosome patterns in parthenogenetic embryos at 0, 24, and 48 hours of development confirmed this trend: haploid cells dropped from about 39 percent of the population to about 20 percent over two days, while diploid cells rose from about 21 percent to 42 percent.3Journal of Veterinary Science & Technology. Difference in Chromosomal Pattern and Relative Expression of Development and Sex Related Genes in Parthenogenetic Vis-A-Vis Fertilized Turkey Embryos The transition from a messy mosaic to a mostly diploid embryo appears to be largely complete within the first 48 hours.
Why Parthenogenetic Turkeys Are Always Male
Birds use a sex-determination system that works opposite to the mammalian one. In mammals, females carry two X chromosomes and males carry one X and one Y. In birds, males carry two Z chromosomes (ZZ) and females carry one Z and one W (ZW). The mother always contributes either a Z or a W to her egg. When parthenogenesis occurs and the egg’s own chromosomes are doubled, an egg carrying a Z becomes ZZ, producing a male. An egg carrying a W becomes WW.
WW embryos do not survive. Chromosome studies show that early blastoderms carrying the W chromosome become lethal within about two days of incubation.2PubMed Central. The Chromosomes of Turkey Embryos during Early Stages of Parthenogenetic Development The W chromosome on its own apparently lacks enough genetic information to support development past the earliest stages, so WW combinations are a dead end. Only ZZ embryos survive to become viable chicks. This means every parthenogenetic turkey that makes it past the first couple of days is male. In one study examining 35 confirmed parthenogenetic embryos, not a single female was found.4PubMed. Differentiating between parthenogenetic and “positive development” embryos in turkeys by molecular sexing
This all-male outcome is a consistent feature of avian parthenogenesis more broadly. A review of the research confirms that diploid parthenogenesis in birds is automictic and facultative, producing only males.5Reproduction. Parthenogenesis in birds: a review
The Parthenogenetic Tom That Fathered Offspring
Most parthenogenetic embryos in turkeys die well before hatching. The rate of development to advanced stages is low, and hatching is rarer still. But the most striking finding from the Beltsville research program is that at least one parthenogenetic male turkey not only hatched and grew to full adulthood but was reproductively functional. This bird, a Beltsville Small White poult that hatched in the spring of 1958, matured and produced semen containing viable sperm.6PubMed. Performance record of a parthenogenetic turkey male
In January 1959, researchers used semen from this tom to inseminate fourteen hens: seven virgins and seven previously mated birds. Of 320 eggs incubated, about 55 percent were infertile, but 122 poults hatched from the 145 fertile eggs, split roughly equally between males and females.6PubMed. Performance record of a parthenogenetic turkey male That fertility rate was lower than what you would expect from a conventionally bred tom, but the key point stands: an animal produced without a father was able to sire normal offspring of both sexes. His daughters carried one set of chromosomes derived entirely from their grandmother’s parthenogenetic contribution and one set from their mothers. In genetic terms, this male was essentially a concentrated copy of his mother’s genome, and yet he produced healthy, fertile young.
Breeding for Higher Rates
Parthenogenesis in turkeys is not an all-or-nothing switch; it appears to be a trait influenced by genetics. Since its discovery, selective breeding on a family basis has been practiced in an attempt to intensify the rate of parthenogenetic development in certain lines of turkeys and chickens.7PubMed. Frequency and cytological aspects of diploid parthenogenesis in turkey eggs The Beltsville Small White line used in most of the classic research was specifically chosen and bred for this purpose, and over generations the frequency of parthenogenetic development in unfertilized eggs from selected hens climbed noticeably compared to unselected lines.
The fact that selective breeding works tells us the tendency toward parthenogenesis is heritable. It is not simply a random accident that any egg might undergo. Some families of turkeys are far more prone to it than others, and the trait responds to selection pressure the same way egg production, body size, or feather color would. Researchers have not pinpointed a single gene responsible; the trait appears polygenic, involving multiple genetic factors that collectively raise or lower the probability that an unfertilized egg will begin developing.
What Gene Expression Looks Like in Parthenotes
More recent work has moved beyond chromosomes and into the molecular details. A microarray study compared gene expression between fertilized turkey embryos and parthenogenetic ones at 0, 12, and 24 hours of development. The differences were substantial: at the start of development, over 2,100 genes were differentially expressed between the two groups. Hundreds of genes were turned up in parthenotes that were turned down in fertilized embryos, and vice versa.8PubMed. Microarray analysis and PCR validation of genes associated with facultative parthenogenesis in Meleagris gallopavo (Turkey) Several genes with significantly higher activity in parthenogenetic embryos are involved in lipid transport, muscle structure, and protein synthesis, which suggests the parthenogenetic embryo is compensating for the absence of paternal genetic contributions by ramping up certain metabolic and structural pathways early on.
The sheer number of gene-expression differences helps explain why so few parthenogenetic embryos survive to hatching. A fertilized embryo benefits from two genetically distinct parents, which provides a broader toolkit of gene variants. A parthenote has only the mother’s genetic material, doubled, so every gene is homozygous. Any harmful recessive alleles the mother carries are exposed with no masking copy from a father. The molecular data suggest that parthenotes are fighting an uphill battle from the very first cell divisions, with large-scale disruptions to normal developmental programming.
Does Parthenogenesis Interfere with Normal Reproduction?
One practical concern for turkey breeders is whether hens prone to parthenogenesis perform worse when they are actually mated. The evidence suggests they do. Virgin quail and turkey hens that exhibit parthenogenesis have reduced reproductive performance following mating.5Reproduction. Parthenogenesis in birds: a review The mechanisms behind this reduced fertility are not fully understood, but one hypothesis is that the cellular machinery geared toward initiating parthenogenetic development interferes with the normal fertilization process. If an egg is already primed to start dividing on its own, the entry of a sperm cell and the coordination of two sets of chromosomes may be disrupted.
This is an area where the science remains thin. The finding has been noted in research reviews but has not been explored in large-scale, well-controlled studies. For commercial turkey operations, where virtually all reproduction is done through artificial insemination, it is unclear whether the effect is large enough to matter at an industry level. The Beltsville Small White line that was heavily selected for parthenogenesis is a research strain, not a commercial one, and modern commercial turkey breeds have been selected overwhelmingly for growth rate and meat yield rather than anything related to parthenogenetic tendency.
How Common Is This in Other Birds?
Turkeys are the best-studied case of avian parthenogenesis, but they are not the only species where it has been observed. Domestic chickens also show the phenomenon, though at lower rates. Beyond poultry, parthenogenetic development that failed to progress to hatching has been noted in captive finches and domestic pigeons.9Oxford Academic (Journal of Heredity). Facultative Parthenogenesis in California Condors The most dramatic recent finding involves California condors. Genetic screening of captive condor populations identified two birds that were produced parthenogenetically, despite the fact that their mothers had access to fertile males at the time. Both condor parthenotes were male, consistent with the ZZ-only pattern seen in turkeys.
The condor discovery was significant because it showed parthenogenesis occurring even when males were available, not just in isolated virgin females. That raises the possibility that facultative parthenogenesis in birds is more widespread than previously appreciated, simply going undetected because nobody thinks to check paternity in a flock with plenty of males around. Genetic screening technology is now sensitive enough to catch these events, and as more bird populations are routinely genotyped, additional cases may come to light.
Parthenogenesis Beyond Birds
Facultative parthenogenesis is not limited to birds. Among vertebrates, it has been documented in sharks, rays, snakes, and lizards. A study of wild pit vipers, for instance, confirmed that females in natural populations produced offspring by parthenogenesis, with the homozygous nature of the young confirming an automictic mechanism similar to what turkeys use.10PubMed Central. Facultative parthenogenesis discovered in wild vertebrates In these snake species, parthenogenesis is clearly a last-resort reproductive strategy rather than the primary mode: females that can find mates reproduce sexually, while those isolated from males occasionally produce young on their own.
The turkey case is unusual among these examples in a couple of ways. First, turkeys are endothermic (warm-blooded), and parthenogenesis is far rarer in warm-blooded vertebrates than in reptiles or fish. Second, the turkey is the only bird in which a parthenogenetic offspring has been confirmed to reach full adulthood and reproduce sexually, closing the loop from fatherless birth back into the gene pool. In most other species where facultative parthenogenesis has been recorded, the offspring are either inviable or their long-term fertility has not been tested.
There is also an important distinction between facultative and obligate parthenogenesis. Some lizard species, for example, reproduce exclusively through parthenogenesis; their populations are all-female. Turkey parthenogenesis is facultative, meaning it can happen but doesn’t have to, and normal sexual reproduction remains the default. The trigger that causes some eggs to start dividing without fertilization while most do not is still one of the open questions in the field. Neither a single environmental cue nor a single genetic switch has been identified, and the honest answer is that researchers still do not have a clear picture of what flips the switch in any given egg.
Practical Meaning for Turkey Farming
If you are raising turkeys, parthenogenesis is not something you need to worry about or plan for. The rates are too low to have any meaningful impact on commercial production, and the vast majority of parthenogenetic embryos die long before hatching. Modern commercial turkey breeds have not been selected for the trait, and the artificial insemination programs used in virtually all large-scale turkey production mean that unfertilized eggs are generally discarded rather than incubated.
Where parthenogenesis does matter is in research and conservation. The condor finding showed that parthenogenesis can produce individuals in endangered species breeding programs, potentially complicating genetic management. A parthenogenetic offspring is highly homozygous, meaning it has far less genetic diversity than a sexually produced individual. In a small captive population where maintaining diversity is the whole point, an undetected parthenote could skew the breeding plan. Routine genetic screening of offspring is the obvious countermeasure, and many captive breeding programs already do this for other reasons.
For evolutionary biologists, turkey parthenogenesis remains a useful model for understanding why sexual reproduction dominates in vertebrates. The low survival rates and reduced genetic diversity of parthenotes illustrate the costs of losing one parent’s genetic contribution. The Beltsville research program, running for decades, essentially ran a long-term experiment on whether you can breed a viable asexual lineage in a warm-blooded vertebrate. The answer is a qualified yes for individual animals, but the consistently poor hatch rates and high mortality suggest that the strategy cannot sustain a population over time without reverting to sexual reproduction.