Parthenogenesis can occur in domesticated chickens and turkeys without the presence of a male, but the embryo typically dies. Only a few reports exist of fatherless male turkeys that survived to adulthood, and only one or two produced sperm.
In birds, parthenogenesis arises from an egg cell that has a single genome copy (haploid). Special cell division called meiosis generates eggs in the ovary of a female, shuffling up the genome, and halving the chromosome count. Male testes use this process to create sperm cells.
Normally, a sperm cell and an egg cell merge (fertilization) that combines the genomes of both parents and restores the typical (diploid) chromosome count. In parthenogenesis, the egg cell does not fertilize. Instead, it attains a diploid state by fusing with another cell from the same division, which is usually discarded, or by duplicating its genome without being divided.
As a result, the resulting egg has only a subset of the mother’s genes in a double dose, rather than one genome from the mother and one from the father.
Fatherless birds are always male because sex in birds is determined by Z and W sex chromosomes. The ZZ combination comprises two copies of the DMRT1 gene and produces a male, whereas the ZW combination has only one copy and produces a female.
Haploid egg cells from the ZW mother receive either a Z or a W. Their diploid derivatives will be either ZZ (normal male) or WW (dead). WW embryos fail to develop because the W chromosome has few genes, while the Z chromosome contains 900 genes vital for development. Therefore, fatherless chicks must be ZZ males, as observed.
Parthenogens (fatherless animals) don’t thrive well. Neither of the two fatherless condors bred on their own. One died before reaching sexual maturity, while the other was weak and submissive, making it unlikely to father offspring.
Parthenogenesis in chickens and turkeys generates either dead embryos or weak hatchlings. Although female-only lizard species appear robust, they are typically the product of recent species blending that went wrong during meiosis, leaving them with no other option. These species do not survive for long.
The answer to why parthenogens do so poorly lies in the core of a fundamental biological question – why sex exists. It would seem more efficient for the mother’s genome to be simply passed down to her clonal offspring without bothering with meiosis.
Variation is Crucial
Although having a genome consisting solely of the mother’s genes may seem like a good idea, it is not healthy according to research. The health of an individual and its species depends on genetic variation, and mixing gene variants from both male and female parents is essential.
In diploid offspring with two parental genomes, healthy variants can compensate for mutations. Individuals who inherit genes solely from their mother may have two copies of a maternal mutant gene that weakens them, without a healthy version from a male parent to offset it.
Genetic variation also plays a vital role in protecting populations from deadly viruses, bacteria, and parasites. Meiosis and fertilization produce many rearrangements of different gene variants, which can confuse pathogens. Without this added protection, pathogens could easily infect a population of clones, and a genetically similar population would not contain resistant animals.
Therefore, the ability of condor females to produce chicks without a father is unlikely to save the species. However, human efforts have now resulted in hundreds of both female and male condors soaring through California’s skies.
Jenny Graves, a distinguished genetics professor and vice chancellor’s fellow at La Trobe University in Melbourne, Australia, authored this article.
This article is republished from The Conversation under a Creative Commons license. The original article can be found here.
FAQ
1. What is a ‘Virgin Birth’ in relation to California Condors?
A ‘Virgin Birth’ in relation to California Condors, also known as parthenogenesis, refers to the ability of a female condor to produce offspring without mating with a male. This is a rare phenomenon in the animal kingdom and was first discovered in captive populations of birds in the 1950s. Recently, it was discovered that a female California Condor living in the wild had produced a chick through parthenogenesis, sparking hope for the species’ survival.
2. Why is the ‘Virgin Birth’ important for the conservation of California Condors?
California Condors are critically endangered, with only a few hundred individuals remaining in the wild. The ‘Virgin Birth’ offers a glimmer of hope for the species’ survival as it provides a way for females to reproduce without the need for a male partner. This could potentially increase the genetic diversity of the population, which is crucial for the long-term survival of any species.
3. How does parthenogenesis occur in California Condors?
Parthenogenesis occurs in California Condors when an egg is fertilized by a sperm cell but the male’s genetic material is not incorporated into the embryo. Instead, the egg begins to divide and develop on its own, leading to the birth of a female chick with genetic material identical to its mother. This process is rare and occurs spontaneously, without any external intervention.
4. Are there any potential drawbacks to relying on ‘Virgin Births’ for the conservation of California Condors?
While the ‘Virgin Birth’ offers hope for the survival of the California Condor, it is not a silver bullet solution. Parthenogenesis typically only produces female offspring, which could limit the genetic diversity of the population over time. Additionally, it is not clear how often parthenogenesis occurs in the wild and whether it could be relied upon to save the species from extinction.
5. What other conservation efforts are being made to save the California Condor?
In addition to the potential of ‘Virgin Births’, other conservation efforts are being made to save the California Condor. These include captive breeding programs, habitat restoration, and efforts to reduce human-caused threats such as lead poisoning and collisions with power lines. These efforts are all aimed at increasing the population and genetic diversity of the California Condor to ensure the species’ long-term survival.
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