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The Lost Crown of Henry VIII
Many of the most amazing historical crowns were destroyed during the tumultuous hurly-burly of history. This is a reproduction of the crown worn by the infamous Henry VIII, the powerful plus-sized king with many wives. The original was made either for Henry VIII or his father Henry VII and was worn by subsequent Tudor and Stuart monarchs up until it was broken apart & melted down at the Tower of London in 1649 under the orders of Oliver Cromwell (when the monarchy was abolished and replaced by the Protectorate). The original crown was made of solid gold and inset with various rubies, emeralds, sapphires, spinels, and pearls. After Henry VIII’s schism with the Catholic Church, tiny enameled sculptures of four saints and the Madonna and child were added to emphasize the monarchy’s authority over the Church of England.
Charles I of the United Kingdom (Charles Mytens, 1631)
Although the reproduction was not made with solid gold or natural pearls (which would be prohibitively expensive) it was painstakingly crafted by master jewel smiths using period techniques. The jewelers were able to recreate the original crown in great detail because many paintings and descriptions are available, including the amazing picture of Charles I by Daniel Mytens above. Charles I lost his head and the crown with his obdurate insistence on the absolute authority of the monarch—a point of view which Cromwell sharply disputed.
A Honeybee Drone
Even though honey bees they mimic humans in some ways (for example with their rigidly hierarchical hive organization), they are alarmingly alien in many respects. Nowhere is this more in evidence than in the lives of honeybee drones—the male bees which play a role in reproduction but are otherwise alarmingly superfluous to the workings of a bee hive.
Drones are born from unfertilized eggs either laid by queens or by laying worker bees (which can only lay drones). Because the drones develop from unfertilized eggs they have only one set of chromosomes (a reproductive process known as arrhenotokous parthenogenesis) and each drone produces genetically identical sperm. A fertilized queen can lay female worker bees which have two sets of chromosomes (diploid). Worker bees are extremely closely related as sisters since they share identical genetic information from the father (as opposed to most other animals where male sex cells are not all genetically identical).
Drones do not posess stingers and can be safely handled.
Drones are different in appearance from female bees. They are slightly larger than worker bees but smaller than the queen. They have extremely large eyes, perhaps to help them find a queen while flying. Additionally, drones lack stingers (which are really modified ovipositors and thus unique to female bees). Drones from different hives congregate at certain locations not far from a given hive (it is unclear how they choose or mark these locations).
Drones do not engage in the useful toil so characteristic of the workers. Male bees do not gather nectar & pollen, take care of larvae, or build the hive. Lacking stingers, they do not act as soldiers. Their only purpose is to mate with a queen—though only one in thousands will fulfill this destiny. Mating is accomplished in midair and proves fatal to the drone. His reproductive organs break off inside the queen and the contusion proves mortal. Drones have no place in an austere winter beehive. As winter approaches in cold weather locations, worker bees cast all of the drones out of the hive to perish.
Regular readers know how much I esteem turkeys. Unfortunately I worry that my writings are not winning additional admirers for these astonishing birds. It is time to play a trump card and reveal one of the great bizarre strengths of turkeys. They are capable of virgin birth.
A New Mexico Whiptail (Aspidoscelis neomexicana). All New Mexico Whiptails are female. The entire species reproduces by parthenogenesis.
Before you spring up in alarm and start shouting, allow me to present a miniature biology lesson. Parthenogenesis is a form of asexual reproduction. Some female organisms are capable of producing an ovum which develops into a new individual without being fertilized by a male gamete. In these cases, the mother contributes her genetic material to the offspring. Although natural parthenogenesis is frequently observed in rotifers, insects, mollusks, crustaceans, and flatworms, this method of reproduction is much less common among vertebrates. However a few species of fish, amphibians, and reptiles are known to reproduce via parthenogenesis (movie-goers may recall that this happened to the dinosaurs in Jurassic Park.) The turkey is very unusual in being a bird which can reproduce through this means (or at least we think it is unusual—perhaps parthenogenesis is more common among birds then we realize but we just don’t know about it except in settings like farms where it becomes obvious). Chickens can also produce self-fertilized eggs but they almost never develop beyond embryonic stages, whereas female turkeys can and frequently do produce living offspring which lack fathers.
This diagram from the BBC actually explains shark parthenogenesis but you get the idea.
Parthenogenesis occurs in turkeys through the doubling of haploid cells. Biologists have discovered that the rate at which this occurs can be increased by selective breeding. Poults produced by parthenogenesis are capable of growing into healthy viable toms indistinguishable from toms with more traditional parentage. You will note that I wrote “toms”—all turkeys conceived via parthenogenesis were created from doubled haploids and are are homogametic. Consequently they are all all male. (This will leave mammal enthusiasts scratching their heads–since female mammals are homogametic and have two x chromosomes. However for birds and for some reptiles, males have two Z chromosomes and thus are the homogametic sex. In such species, females have one Z and one W chromosome and are the heterogametic sex.)
Mammals do not naturally utilize parthenogenesis as a method of reproduction. Certain portions of mammalian genes consist of imprinted regions where portions of genetic data from one parent or the other are inactivated. Mammals born of parthenogenesis must therefore overcome the developmental abnormalities caused by having two sets of maternally imprinted genes. In normal circumstances this is impossible and embryos created by parthenogenesis are spontaneously rejected from the womb. Biology researchers have now found ways to surmount such obstacles and a fatherless female mouse was successfully created in Tokyo in 2004. With genetic tinkering, human parthenogenesis is also biologically feasible. Before his research was discredited and he was dismissed from his position, the South Korean (mad?) scientist Hwang Woo-Suk unknowingly created human embryos via parthenogenesis. To quote a news article by Chris Williams, “In the course of research, which culminated with false claims that stem cells had been extracted from a cloned human embryo, Hwang’s team succeeded in extracting cells from eggs that had undergone parthenogenesis… The ability to extract embryonic stem cells produced by parthenogenesis means they will be genetically identical to the egg donor. The upshot is a supply of therapeutic cells for women which won’t be rejected by their immune system, without the need for cloning.”
All of which is fascinating to biology researchers (and those who would seek greatly prolonged life via biogenetic technologies), however it seems that in nature, the turkey is the most complicated creature capable of virgin birth.
A life cycle diagram is a stylized pictorial representation of the path an organism must undergo in order to renew itself and continue living for multiple generations. For example here is a very simple life cycle diagram of a human.
A few details might have been glossed over...
Straight forward enough: the person begins where the two red lines intersect as a little zygote—with genes from both mother and father. The zygote matures in the mother’s womb, is born, grows up to sexual maturity (notice the awkward puberty phase), and then contributes a single haploid reproductive cell to combine with the haploid reproductive cell of the opposite gender mate. Voila: another zygote which becomes a fetus and begins the cycle again! A more creative artist could have provided a bit more context (for example see the adorable penguin life cycle below), but, minus some snappy duds and sharp patter, humankind’s path to continued existence is pretty much all there.
Aw! It's like they're wearing little tuxedos!
The story starts getting more convoluted as we examine organisms that are less familiar. Here for example is the life cycle of a hornwort.
Argh! What is going on here? In fact, what is a hornwort anyway?
To start with, hornworts are ancient land plants which trace their origin back to before the Devonian (416 million years ago). These non-vascular plants were one of the first organisms to colonize the barren continents, back when life was mostly an ocean-only affair. To allude to a different post, they were one of the original invasive species on land.
The hornwort’s life cycle is alien to us because the plant, like almost all plants and fungi (and like some protists), utilizes alternation of generations to reproduce. Looking at the diagram it is hard to choose a place to start from: spore, egg, gametophyte? But if our human diagram weren’t so familiar, it would be difficult to find the starting place on it too. Life cycle diagrams have a “chicken or the egg?” paradox built in to them.
For the hornwort, let’s start with the spore. There it is in the upper right corner like a little cube of cheese. It is a haploid cell–having only one set of chromosomes just like a mammal’s sperm or egg. But it is not like a sperm or egg! Look at the diagram: by itself, it turns into a protonema, the little transitional sprout which develops into the adult gametophyte. The gametophyte is what we think of as the independent living hornwort plant. Once this (still haploid) plant has grown to adult size it produces haploid sex cells in special structures called the antheridium (male cells) and the archegonium (female cells).
For the next stage, water is required so that the sperm can swim to the egg which remains stationary in the archegonium. This is why hornworts could not leave damp watery areas. The sperm and egg combine to form a diploid zygote (with two sets of chomosomes just like in the human zygote and the human adult!) which develops into a sporophyte. The sporophyte remains dependent on the gametophyte out of which it sprouts. The life cycle diagram magnifies a section of the sphorophyte–which is portrayed as a complicated green tube along the right of the picture. Inside the sphorophyte, within sporogenous cells, meiosis takes place and new haploid spores are created. When they are ready, the sporophyte capsule breaks open and the spores are released to in turn become protonema and begin the process again.
Although I have chosen the unfamiliar hornwort as an example, the underlying life cycle of familiar angiosperm (flowering) plants such as my beloved roses is not dissimilar.
Hmm, the terminology and morphology are pretty different though...
To quote Wikipedia, “alternation of generations implies that both the diploid and haploid stages are multicellular.” This is important: if we thought of the unicellular sperm (or the egg) from the diagram at the top as a separate entity from ourselves, humans would reproduce by a sort of separation of generations, but we don’t really think of our conception that way!
ferrebeekeeper 