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50

The question is relatively broad and one should take into account that the brain not only consists of neurons, but also glial cells (supportive cells) and pre-mitotic neuronal stem cells. Furthermore, as critical fellow-scientists have indicated, developmental stage is very important, as the developing embryonic brain is very different from the adult brain. ...


18

There is some evidence that fetal development under zero gravity conditions might be problematic. Wakayama S, Kawahara Y, Li C, Yamagata K, Yuge L, et al. (2009) Detrimental Effects of Microgravity on Mouse Preimplantation Development In Vitro. PLoS ONE 4(8): e6753. doi:10.1371/journal.pone.0006753 The paper is here. These authors studied aspects of ...


14

From a certain point of view you could argue that our bodies have an inherently limited lifespan; Telomeres are extensions to the end of chromosomes that prevent damage or loss of genetic information during cell division. Telomeres are not replaced (in normal cells), which gives rise to a replicative lifespan; the number of times a cell can divide before ...


12

Seeds are spread by many mechanisms Wind dispersal: When air currents used to spread seeds. Often these plants have evolved features to facilitate wind catching, for example dandelions. Aka, anemochory. Propulsion & bursting: When seeds are propelled from the plant in an such as in these videos. This is called Ballochory. Water: Similarly to wind ...


11

First of all: Yes, fluoride is toxic, but the toxicity depends largely on the form (soluble vs. unsoluble, which fluoride salt etc.) occurs. It also depends on the environment since insoluble salts which are subjected to strong acids can release fluorine ions. The certain toxic dose for adults is 32-64mg/kg body weight, a 75kg adult needs to take up between ...


10

In utero, the growing little human is getting ready to be an independently functioning individual. While it is everything but that, it must be able to obtain fluids and nutrients through its mother's milk, and that from pretty much the first hour of its life. To develop proper kidney function, the growing fetus needs to ingest fluids just as it will do post ...


9

In my experience (in common with the experience of everyone I've talked to who could be considered an expert on the subject), taking old wood and using that as a scion when grafting new trees rejuvenates them, and they grow as new trees. I'll take apple trees as an example. As you can see from the table here, there is a distinct age after which the tree ...


8

Cell-cell adhesion is a well-regulated mechanism, cells don't just stick together randomly, this interaction is mediated by specific molecules on the cell surfaces. The responsible proteins for that are the Cell Adhesion Molecules (CAMs) like integrins, cadherins and selectins. Which of these CAMs are present on the surface of a cell determines if those ...


8

You may want to look into "Evolutionary - Developmental Biology", which deals with how an embryo develops into a grown organism. Thus, by combinatorial specifying the identity of particular body regions, Hox genes determine where limbs and other body segments will grow in a developing embryo or larva. A paragon of a toolbox gene is Pax6/eyeless, ...


8

Short answer: Changing something (instead of everything) yes. There are several studies on the impact of environmental factors on life span. Of course it depends from organism to organism. Diet restriction for example has been shown to extend life span of worms and mice. Temperature is also working well, at least with microorganisms, the metabolism of ...


7

The answer is more or less yes. Normally Firebugs (Pyrrhocoris apterus) go through 5 nymph instar stages (as do most Hemiptera), where they resemble the adults more and more as they grow. Only adults are winged and have have functional reproductive organs. This type of metamorphosis is called hemimetabolous or simple metamorphosis (in contrast to ...


7

This is a very interesting question. Many people have researched this topic, and many still are. But regardless, I had never heard of Alan Turing's contributions, so thank you! First of all, I cannot actually find who first coined the term morphogen. Though people had hypothesized that chemicals could play a critical role in development through much of the ...


7

First of all, I should quote the sentence from the MOST reliable ophthalmology sourcing in the world - American Academy of Ophthalmology: Section 11 - "Lens and Cataract" "The equatorial diameter of the unfixed human lens measures 2 mm at 12 weeks and 6 mm at 35 weeks. Both the growth and the maturation of lenticular fibers continue throughout life." The ...


7

No, fish scales are dermal (= formed in derma) bones like skull roof bones. Scales in reptiles are formed by epidermis and are made primarily of protein (from keratinocytes), being similar in derivation to hair, feather and nails. On the other hand, in reptiles one must differentiate between scales and osteoderms (= scutes). Scutes are widespread among ...


7

To add to Christiaan's answer, I'll mention one striking example of long-distance neuronal migration in the adult mammalian brain: the so-called Rostral Migratory Stream found in rodents, in rabbits and both the squirrel and rhesus monkey. Neuronal precursors originating in the subventricular zone (SVZ) of the brain migrate to reach the main olfactory bulb ...


7

There are legitimate case reports in credited journals of hyperdontia, or the condition of having supernumerary teeth. Such cases are often associated with congenital syndromes-- cleft lip and palate, trichorhinophalangeal syndrome, cleidocranial dysplasia, and Gardner's syndrome. I included a case report and a comprehensive review for you below. Case ...


7

Resemblance between parent and offspring is certainly true. Some traits are more obvious than others, for example skin colour would be very obvious. As babies mature they will gradually begin to look more and more like their parents, the features of babies often change rapidly, for example pretty much every baby has a little nose, but by the time they are a ...


6

Cell differentiation, cell fate and cell mapping is an interplay of accessible evolutionary strategies/programmes and responses to dynamic environmental cues such as specialized hormones (e.g. morphogens) and physical parameters and constraints. That is putting it very broadly. It is a complex issue, if L. Wolpert's PLOS assays are any indication. I compiled ...


6

No. In fact the lens of the eye, which is nearly optically perfect in humans, does not change or grow after it is fully formed around week 26 of gestation. Interestingly this is why one of the cues for identifying young children is having small faces with large eyes. This also the case for puppies and cats and other animals, who are mostly cuter when they ...


6

Oocytes, or immature female eggs, develop in the fetus's ovaries during pregnancy. This graph (U. New South Wales) shows the oocyte population over time in a human female: Although the x-scale is kind of confusing (months when negative, years when positive), you can see that the fetus has all the oocytes it will ever have at the peak 18-22 weeks after ...


6

It is impossible at present to reproduce all the conditions of a womb. A womb is more than a warm fluid-filled home for nine months. A few days after fertilization, the trophoblast portion of the conceptus attaches itself to the uterine wall where it develops into a placenta and umbilical cord while the rest (the epiblast) becomes the baby. Throughout the ...


6

Artificial amniotic fluid has been used on goats, and for premature human babies. In the 1996 experiment, Thomas Shaffer, a scientist at Temple University, used an oxygenated liquid in a clinical trial with thirteen infants born at twenty-three to twenty-four weeks who were not expected to survive, and seven babies were discharged healthy. Jonathan Knight, ...


6

In short, without direct physical evidence (forensic or medical examination), testimony, or documentation to act as proof, you are left up to the discretion of the court to determine whether evidence is admissible and up to a jury to decide if it is reasonable to presume that a person depicted is of a certain age if no other evidence to the contrary is ...


6

A review paper on children born by the advent of assisted reproductive technologies (ART) and frozen sperm (Lansac & Royere, 2001) concludes that ART children, as compared to the general population: Have normal weight; Do not suffer increased occurrence of premature births; Do not have increased rates in stillbirths; Have equivalent sex ratios; Show no ...


5

Just so that someone answers this question so that the moderators have less work to do: The fundamental reason why embryos don't get massacred by the maternal immune system is because of the placenta and several of its functions. Three mechanisms are: 1) Secretion of neurokinin B, which is also secreted by parasites to avoid detection of the host. 2) The ...


5

Many genetic studies in this area have found that variation in serotonin receptors associates with differences in a number of personality traits. That one gene, or a very small number, turns up time and time again for something so complex as human personality makes me a bit suspicious. Other factors at play: Family dynamics Culture and cultural norms ...


5

The urogenital system as a cohesive functional unit probably evolved very early in vertebrate history. Hagfishes and lampreys have separate systems for reproduction and excretion. More derived groups of fishes use kidney tubules and ducts for sperm delivery outside the body (Helfman et al. 2009). The vertebrate nephron may be homologous to the invertebrate ...


5

I don't know if this is what you mean, but take a look at BioNumbers. Also, mathematical constants like pi are different from physical constants. Mathematical constants are true in a mathematical (logic) sense, and do not need to be related to any physical quantity. They are derived by logic. Physical constants, on the other hand, typically describe an ...


5

That is highly unlikely. The article to which you linked specifically states: While watching other people exercise may increase your heart rate and have other physiological effects, nothing can replace the health benefits of getting off the couch. With proper nutrition, muscle is built through exercise by adding sarcomeres [to muscle cells which ...


5

The umbilical cord, which contains the umbilical arteries and vein so important for nutrient, oxygen and waste transport before birth, becomes useless pretty much the moment the lungs start working (the kidneys already started before birth). As the baby breathes, the two arteries constrict to stop flow from the newborn to the placenta. The Wharton's Jelly, a ...



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