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Project Runway for Tortoises

A heart warming tale of how 3D printing may have saved a young tortoise from a damaged carapace. 

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Cleo Gets a Coat!

⎈ Cleopatra is a teenager who seems pretty happy with her bright, new red coat. What's unusual is that Cleo is a leopard tortoise! Also, her coat was 3D printed from a corn-based polylactate polymer by student designers at Colorado Technical University. No, this isn't a new challenge on Project Runway, although the coat does stylishly drape over Cleo's shell. It's actually a 600 hour labor of love that will hopefully let Cleo enjoy a long (80+ years), tortoise life. 

⎈ Tortoises in the wild have smooth and convex shells. Unfortunately, when bred in captivity, tortoise shells grow in raised bumps known as pyramiding. When Cleo horsed around with her tortoise friends, the deformed shell wore through in spots, making her susceptible to bacteria and other infections. Fortunately, her red coat is temporary and her shell is expected to heal in a few years. 

⎈ Scientists are not sure what causes pyramiding. Too much dietary protein (Cleo is a herbivore) is one culprit. Not enough bone calcium is another. One study showed that raising the humidity helped. Until we solve the problem or stop breeding tortoises in captivity, we have prosthetics -not just for humans, but for our four legged friends too. 

News Story: http://goo.gl/qtZw7V

Ref: Influence of environmental humidity and dietary protein on pyramidal growth of carapaces in African spurred tortoises (Geochelone sulcata) (2003). C. S. Wiesner andC. Iben. Journal of Animal Physiology and Animal Nutrition. Volume 87, pages 66–74
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Drought in California

More sobering facts to ponder this World Water Day.

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Global Warming - California Drought
A year ago I posted this http://goo.gl/KSMkib about future water problems and got a lot of flak from naive people who can't understand that it will be a lot worse, that one day the water will stop flowing. The California drought is now a fact. 
Moronic uneducated climate change deniers can throw snow balls to prove the opposite but the numbers show that Global warming will become worse, that it could be even worse than we expected.

This year with low gas prices, the sale of gas guzzlers and SUVs skyrocketed in Canada and elsewhere!

Descensus ad inferos
#globalwarming   #globalwarning   #climatechange   #water   #california  
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IPCC reports  http://goo.gl/3GSu8
Warming Pushes U.S. to Driest Period in 1,000 Years
http://goo.gl/fqm3bT
California Drought  http://goo.gl/FHPZGN
Time to get serious about the California drought http://goo.gl/LCtSAb
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In the Balance: From Autism to Cancer

The discovery of a gene implicated in both autism and a deadly form of brain cancer reveals the importance of gene dosage in biology. Not enough of a proton leak through a transporter protein named NHE9 leads to neurodevelopmental defects associated with autism. On the other hand, too much of NHE9 has poor prognosis in patients with glioblastoma multiforme. Find out why in the #ScienceSunday  post!

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What Autism can Teach us about Brain Cancer

Glioblastoma multiforme, or GBM, is a deadly cancer with median survival of only 12-15 months. Recently, we found a gene that had been previously implicated in autism to also contribute to GBM. The gene NHE9 makes a protein that exchanges sodium ions for hydrogen ions (also called protons) across the boundaries of endosomes, hence it's moniker "sodium-hydrogen exchanger". But what are endosomes and why is the function of NHE9 important?

Highway Traffic: All cells contain many “cargo packages” surrounded by membranes, depicted in the expanded view as a blue compartment in the figure below. These so-called endosomes carry newly minted proteins to specific destinations throughout the cell and haul away old proteins for destruction. Key to their “shipping speed” is the level of acidity inside the endosomes. Acidity relates to the number of protons, which are controlled by balancing the activity of “pumps” that push protons into endosomes to increase their acidity with that of “leaks,” like the protein NHE9, that remove protons. 

There's a Hole in the Bucket: You can think of endosomes as leaky buckets of water. Altering either the faucet or the leak rate can dramatically change the water level in the bucket. In autism, NHE9 is mutated and non-functional. In the absence of proton leak, the endosomes become too acidic and prematurely clear away important proteins on nerve ends, leading to neurological dysfunction. Helper cells called astrocytes cannot clear away neurotransmitter signals fast enough, and this leads to hyperexcitability or seizures associated with autism.

Too Much of a Good Thing: in contrast to autism, NHE9 is overactive in brain cancer, causing endosomes to leak too many protons and become too alkaline. This slows down the “shipping rate” of cancer-promoting cargo and leaves them on the cell surface for too long where they inappropriately prolong signals of growth and migration, the two main characteristics of invasive cancer cells. Fortunately, when the leak is plugged by inhibiting NHE9 with drugs, tumor growth is blocked. Currently, the drugs are not good enough to use on patients, so an important step going forward will be to discover better drugs that target NHE9. These could be used in combination with other drugs for treatment of this deadly disease. 

Paper: A leak pathway for luminal protons in endosomes drives oncogenic signalling in glioblastoma. Kondapalli et al. (2015) Nature Communications http://goo.gl/dAa5NG

Johns Hopkins News Story: http://goo.gl/XAsGDb

A Part of the Puzzle: NHE9 and Autism https://plus.google.com/u/0/+RajiniRao/posts/fsNzo1yKsQG

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Cuddling some fish eggs
Thanks +Aida Hazlan for sharing this interesting post about the development of cuttlefish.

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Watcher in the Egg

After a female cuttlefish spawns, or lays her eggs, in inky, grapelike clusters on the seafloor, she leaves them to mature on their own for about two months. During that time, the egg sacs grow thinner and clearer, losing their inky camouflage and, within a week or two of hatching, allow the baby cuttlefish to peer out of its protective bubble. By the time it hatches, a cuttlefish is completely prepared for a life of hunting shrimp and evading predators.

 A study recently published in the British journal Animal Behavior (http://goo.gl/mHEzPv) shows that common cuttlefish (Sepia officinalis; small, shallow-water animals related to squid and octopi) can learn to recognize prey even before they hatch. It’s the first time any animal has been proven to learn visually while still in the embryonic stage.

Source: http://goo.gl/wxcVSH

#scienceeveryday   #embryo   #cuttlefish   #marinelife  
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A GIF showing a slice of pi
We hope you had a happy Pi Day.
Thanks +Aida Hazlan.

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Happy Pi Day

This GIF is a visual representation of C = 2r*π (the relationship between the circumference and the diameter).

Source : http://goo.gl/IGiqXi #piday2015 #mathematics #scienceeveryday   #PiDay  
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Not hearing about Pi Day until next year, that's my dream.
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Women in Science

+Science Bulletins at AMNH has been filling the day with posts to highlight different women making great contributions to science. Here is one of the posts, courtesy of +Mindy Weisberger.

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Our next featured scientist for #InternationalWomensDay  is immunologist Dyann Wirth. Together with her team at the Harvard School of Public Health, she is studying the evolutionary adaptations of Senegalese people and their malaria parasites in the field and in the lab.

Find out how seeking signs of natural selection at a molecular level will help fight malaria in a smarter way, in the Human Bulletin: Malaria—Natural Selection and New Medicine.

https://www.youtube.com/watch?v=JPYRpAVc83M&t=105

#IWD2015  
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Have them in circles
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Imagine a World Without Color

Color blind people have defective vision and spend their lives never seeing parts of the spectrum of light. Now +Valspar Paint teams up with scientists to bring color to their world. A touching story via +Cliff Bramlett for #ScienceEveryday  .
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+Steve Esterly I personally find that polarised lenses help, just by improving contrast in general. 
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World Water Day

In recognition of World Water Day today, here is an innovative greenhouse that traps evaporation to collect safe drinkable water in the condensate. This post comes to us via +Dan Radice who says, "A SIMPLE BUT POWERFUL CONCEPT: As someone who camps, I've witnessed my own small tent collect enough water to fill a coffee mug in the morning. I'm wondering if I could utilize the same technology on a problem area in my own back yard and give myself a break in my water bill!"

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Ethiopian dew collector.
Roots Up’s Dew Collector green house can help farmers in arid climates raise fresh vegetables by trapping dew and water droplets in a fillable cistern.
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+LL Pete
It may sound counterintuitive, but it's actually poverty that causes the overbreeding problem that's so common in poverty stricken places.  But of course, we'd all rather ignore these problems in our world than take any action or even encourage others to take action.  Easier to pretend it doesn't matter because "they're over there, so why should I worry about it?"
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Cancer Genetics Meets Mathematics

Our G+ resident math expert, +Richard Green , introduces us to a mathematically precise way of measuring chromosomal breaks in cancer.

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Hultman numbers: measuring genetic distance

If two genomes contain the same genes, but they have been rearranged by a sequence of reversals, translocations, fusions and fissions, how can we measure how closely related the two genomes are? It turns out that a key parameter in this problem is the number of cycles in the graph shown on the right of the picture. These cycles are enumerated by the Hultman numbers.

It is possible for a genome to experience genome rearrangements, which are evolutionary events that change the order of the genes in a genome. However, a single genome rearrangement will not scramble the genes in a random permutation, but instead it will typically cut the genome in a small number of places and reattach the pieces in a different order. A genome rearrangement that cuts the genome in exactly k places is known as a k-break.

The most common types of genome rearrangement can be modelled as 2-breaks, (also known as Double-Cut-and-Join, or DCJ) which means that the genome is cut in exactly two places and the resulting pieces reattached. Examples of such rearrangements include reversals, which flip segments of a chromosome; translocations, which exchange segments of two chromosomes; fusions, which merge two chromosomes into one; and fissions, which split a single chromosome into two. The 2-break distance (or DCJ distance) between two genomes is the smallest number of 2-breaks required to transform one of the genomes into the other. 

An easier special case of the problem treats the case where the genome consists of one chromosome that is linear (as opposed to circular); in other words, the genome consists of a one unbroken string of genes. Each gene in the genome is considered to have a head and a tail, which gives it an orientation. It is also convenient to include a virtual gene numbered 0 which, if it actually existed, would link the last gene in the genome to the first gene.

The diagram on the left of the picture shows the genome graph of a toy model of a genome called Q, which has five genes numbered 1 to 5, together with a virtual gene, numbered 0. The genes in Q are denoted by solid line segments, with an arrow pointing from the tail of the gene to the head. (The tail and head of a gene are indicated by the superscripts t and h, respectively.) The dashed lines show the order in which the genes are connected in the genome. This information can be represented more concisely by the signed permutation (1, –3, 5, 2, –4). If we ignore the signs, this gives (1, 3, 5, 2, 4), which is the order in which the genes appear in the genome, reading clockwise from the virtual gene 0. The negative signs appear in front of 3 and 4 to signify that the orientation of those genes is opposite to that of the other genes.

If we define the genome P to be the one corresponding to the signed permutation (1, 2, 3, 4, 5), then we see that P and Q have the same genes, but in a different order and with different orientations. The diagram on the right of the picture shows that breakpoint graph, G(P, Q), which can be used to visualise the evolutionary closeness of P and Q. The numbers with superscripts that appear around the perimeter of the breakpoint graph are the same ones that would appear in the genome graph of P if we drew it, and the solid lines in the breakpoint graph correspond to the dashed lines in the genome graph of P. On the other hand, the dashed lines in the breakpoint graph correspond to the dashed lines in the genome graph of Q. For example, there is a dashed line from 2^t to 5^h in the breakpoint graph of G(P, Q) because there is also a dashed line from 2^t to 5^h in Q, even though the line itself appears in a different position.

The key feature of the breakpoint graph is the way it decomposes into cycles. For example, the graph G(P, Q) shown on the right of the picture splits up into three cycles, each of which contains some dashed edges and an equal number of solid edges. A cycle containing r dashed and r solid edges is called an r-cycle. In our example, the breakpoint graph contains one 1-cycle (involving the points 0^h and 1^t), one 2-cycle, and one 3-cycle. It is a theorem about breakpoint graphs that the 2-break distance between genomes P and Q is equal to n+1–c, where n is the number of genes (5 in our case) and c is the number of cycles in the breakpoint graph (3 in our case). In other words, the 2-break distance between P and Q is 3 (because 3=5+1–3). 

The (signed) Hultman number H(n,d) is the number of unichromosomal genomes with n genes whose breakpoint graph (relative to a fixed genome) contains a total of d cycles. There is a closed formula for these numbers, but it is rather complicated. The recent paper Generalized Hultman Numbers and the Distribution of Multi-break Distances by Nikita Alexeev, Anna Pologova, and Max A. Alekseyev (http://arxiv.org/abs/1503.05285) generalizes the notion of Hultman numbers from the context of 2-break distance to the context of k-break distance. Although k-break distances have not been observed in evolution, they are used in cancer genomics to measure a catastrophic event called chromothripsis in which multiple breakages happen simultaneously. The authors give recurrence relations for the generalized Hultman numbers in the unichromosomal case, but no closed formula. They intend to treat the multichromosomal case in a future paper. Asymptotically, the 2-break distance is known to be normally distributed, but it is not known what happens for general values of k.

Relevant links

The paper Efficient sorting of genomic permutations by translocation, inversion and block interchange by S. Yancopoulos, O. Attie, and R. Friedberg contains many interesting results in this area. It is freely downloadable from http://bioinformatics.oxfordjournals.org/content/21/16/3340.full.pdf+html

The unsigned Hultman numbers deal with the case where the orientations of the genes are ignored. The unsigned and signed numbers appear in the On-Line Encyclopedia of Integer Sequences at https://oeis.org/A164652 and https://oeis.org/A189507 respectively.

Wikipedia on chromothripsis: http://en.wikipedia.org/wiki/Chromothripsis

This post is about the applications to genomics that I mentioned in passing in a previous post about pancake sorting. You can find the earlier post here: https://plus.google.com/101584889282878921052/posts/GyEPJkT5769

The picture comes from page 3 of the arXiv paper by Alexeev, Pologova and Alekseyev discussed above.

#mathematics #genetics #sciencesunday #spnetwork arXiv:1503.05285
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makes you wonder what the genome of a horse and zebra look like.
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SciTech digest 15 March 2015
Thanks as always +Mark Bruce and happy Ides of March.

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SciTech #ScienceSunday Digest - 11/2015.
Permalink here: http://www.scitechdigest.net/2015/03/editing-mammalian-memories-clearing.html

Editing mammalian memories, Clearing sensecent cells, Interesting nanobacteria, Better cyborg cockroaches, Printing custom molecules, AFM neuron imaging, Magnetic brain stimulation, Flexible colour changes, Silicon fullerane, Farm in a box.

1. Editing Memories While Animals Sleep.
This week researchers demonstrated how to controllably modify certain memories stored in the brains of mice while they sleep http://spectrum.ieee.org/tech-talk/biomedical/bionics/how-to-insert-a-memory-into-the-brain-of-a-sleeping-mouse. They accomplished this by (i) implanting electrodes into the hippocampus of the mouse and measuring the electrical activity while the mouse explored a new environment, correlating particular patterns of activity with particular locations in the environment, and (ii) when the mouse slept and these particular patterns were again activated as part of sleep activity, the researchers stimulated another set of electrodes in another part of the brain responsible for reward and pleasure. This directly modified the memory and resulted in the mouse seeking out only those areas of the environment that were now associated with reward and pleasure. 

2. Senolytic Drugs for Clearing Senescent Cells.
Senescent cells that have stopped dividing accumulate with age and accelerate aging and healthspan in many animal models is enhanced by removing these cells. Two compounds - the cancer drug dasatinib and and natural compound quercetin - have been tested for this purpose in mice and resulted in a significant boost to healthspan http://www.scripps.edu/news/press/2015/20150309agingcell.html. The mice benefited from a range of benefits including improved cardiovascular function, better exercise endurance, reduced osteoporosis, lower frailty, and typically with just a single dose - and with the benefits lasting seven months. Very keen to see this tested in humans as soon as possible. 

3. Confirming the Existence of Nanobacteria.
For the first time the existence of nanobacteria has been conclusively proven with demonstration of nanobacteria isolation, imaging, and sequencing http://newscenter.lbl.gov/2015/02/27/ultra-small-bacteria/. These functional bacterial species, which probably rely on other organisms for nutrients to some extent, were isolated from groundwater and found to measure just 200nm or less across; 150 of these could fit inside an E. Coli bacterial cell, and over 100,000 or more might fit inside a human cell. I read this and think of 100,000 little DNA computers churning along in just one of my cells; incidentally the genomes of the nanobacteria measure about one million basepairs in length. Might be a nice little hardware template for engineering to perform other functions within our bodies, entering and exiting cells - also wonder what overlap there is to Craig Venter’s minimal cell? 

4. Improved Interfacing and Control of Cyborg Cockroach Robots.
The development of cyborg insects took another step this week with a new system that improves over the method of inserting electrodes into insect antennae http://rsif.royalsocietypublishing.org/content/12/105/20141363. The system still utilises a “backpack” containing communications, power, and computation, but now involves inserting electrodes far more intimately into the prothoracic ganglia of the prototype cockroaches, and allows remote operation and locomotion control. Limitations include line-of-sight operation but the group hopes to overcome this by incorporating additional sensors and on-board directional error-correction. 

5. 3D Printing Customised Small Molecules.
A new automated 3D printer is able to synthesise small molecules in a modular fashion - such devices are also known as chemputers or chemprinters http://www.hhmi.org/news/3d-printer-small-molecules-opens-access-customized-chemistry. As part of the proof-of-concept the team used a common set of chemical building blocks to controllably synthesise 14 distinct classes of small molecules. The work drew inspiration from cellular synthesis processes, and resulted in collection of hundreds of different, simple chemical building blocks that can be combined together repeatedly to produce more complex molecules; a company has been founded to commercialise. The promise is to one day have a chemical printer in your house able to synthesise any molecule on demand. In related news another new set of chemistries may expand these possibilities even further http://phys.org/news/2015-03-meta-technique-possibilities-molecular.html

6. Dynamic Imaging of Neurons with AFM.
A new long-tip atomic force microscopy technique has been developed for live-cell imaging at extremely high resolutions http://phys.org/news/2015-03-scientists-atomic-microscopy-imaging-nanoscale.html. The new device was used to produce images and movies of nanometer-scale morphological changes occurring in living cells, and showing structural changes in cells after exposure to insulin, as well as growing protrusions from hippocampal neuronal cells. Pretty mind-blowing stuff - movies of phenomena I never expected to be able to see. 

7. Stimulating the Brain with Magnetic Nanoparticles.
A new brain stimulation technique involves injecting iron oxide nanopaticles measuring 22 nm in diameter into the brain and then exposing specific regions to focused alternating magnetic fields http://newsoffice.mit.edu/2015/magnetic-brain-stimulation-0312. The applied magnetic field causes the nanoparticles to heat up, which quickly leads to activation of nearby neurons. This was a basic proof-of-concept study that originally emerged from cancer research that was using the nanoparticles to kill cancer cell in related regions; the nanoparticles can be heated to an amount sufficient to activate the neurons without harming them, and indeed have been used as MRI contrast enhancement agents for many years. A lot more work to be done however. 

8. Precise Forces on New Materials Produce Precise Colour Changes.
A new flexible materials reflects different wavelengths of light depending on how it is stretched and flexed http://www.osa.org/en-us/about_osa/newsroom/news_releases/2015/engineers_create_chameleon-like_artificial_%E2%80%98skin%E2%80%99/. Taking inspiration from how some insects are coloured via nanoscale structural features that reflect certain wavelengths of light, this new material is a thin layer of silicon etched with rows of ridges that has been embedded into a silicone film. The ridges only reflect certain wavelengths of light and by flexing the material the distance between the ridges changes, as does the wavelength of light reflected - with 83% efficiency and able to convert green light to red for example. Further developments should improve this and allow for some pretty interesting applications. 

9. Mimicking Carbon Structures with Silicon: Fullerane.
The two-dimensional silicon analogue of graphene - known as silicene - has been previously demonstrated and is a hot area of research. Now silicon analogues of other three-dimensional carbon molecules have been demonstrated http://spectrum.ieee.org/tech-talk/semiconductors/materials/carbon-buckyballs-have-a-new-silicon-rival. Christened “fullerane” this molecule is comprised of a lone chlorine ion inside a cage of 20 silicon atoms that are attached to and surrounded by a halo of 12 other silicon atoms that are linked to a trio of chlorine atoms. The interesting thing here is that the chlorine-silicons provide functionalisation sites that can allow linking of other molecules or indeed to joining the silicon cages together in two- and three-dimensional arrays.

10. Latest Farm in a Box.
The latest farm-in-a-box builds on other farm-in-a-shipping container projects to create a very attractive unit http://www.treehugger.com/lawn-garden/farm-box-produces-acres-worth-crops-shipping-container.html. The system uses 90% less water and 80% less fertiliser in a complete hydroponic growing and monitoring system that houses 2,800 growing spots in its 30 square meters, which might produce as much food as an entire acre of farmland. I’ve long been a fan of modular, automated food growing solutions such as this that, with the help of a few more technological iterations and cost reductions might really take off to enable more distributed, decentralised, and personal food production.  

Archived: http://www.scitechdigest.net/2015/03/editing-mammalian-memories-clearing.html 
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More Women in Science

From Emilie du Chatelet in the 18th century to Rosalind Elsie Franklin of the 20th century, these woman all made significant contributions to science and advanced their field of research. Thanks to co-curator +Chad Haney for providing the link.

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How many of them do you know?
#internationalWomensDay  and #ScienceSunday  
Before Marie Curie, these women dedicated their lives to science and made significant advances
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A Spectrum of Sexes

+Koen De Paus shares with us a recent article published in Nature that looks at how the simplicity of assigning male and female may not be as simple as it was once believed.

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Sex redefined - Escaping the binary prison

This collection of hard hitting snippets from an excellent Nature article worth reading in full makes clear how the societal boundaries between the sexes are beginning to break down under the weight of reality. Hopefully mainstream knowledge of work like this will ultimately help us move away from having to conform to expectations surrounding both sex and gender.  

As a staunch advocate of transhumanism I can draw a lot of inspiration from the LGBT community who is in many ways our advance guard. For decades they have been trying to establish the right to construe one's own identity instead of being forced into one of the two rigidly defined prefabricated package deals. They have done so in the face of enormous adversity which makes their perseverance especially admirable. Considering that the LGBT community has trouble getting the world to accept them for who they are, it's nigh impossible to imagine a world embracing people for who or what they want to be. If people are forced to make their case by explaining that they were born this way and thus don't have a choice, this does not bode well for the expanded cognitive and morphological rights transhumanism hopes to enshrine.

I can only hope that some day soon my home country of Belgium follows Germany's excellent example and will too introduce a third gender. It's rather infuriating that we currently lack both the common decency and the basic courtesy to implement even the barest minimum.


http://www.nature.com/news/sex-redefined-1.16943

As a clinical geneticist, Paul James is accustomed to discussing some of the most delicate issues with his patients. But in early 2010, he found himself having a particularly awkward conversation about sex.

A 46-year-old pregnant woman had visited his clinic at the Royal Melbourne Hospital in Australia to hear the results of an amniocentesis test to screen her baby's chromosomes for abnormalities. The baby was fine — but follow-up tests had revealed something astonishing about the mother. Her body was built of cells from two individuals, probably from twin embryos that had merged in her own mother's womb. And there was more. One set of cells carried two X chromosomes, the complement that typically makes a person female; the other had an X and a Y. Halfway through her fifth decade and pregnant with her third child, the woman learned for the first time that a large part of her body was chromosomally male.

doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions — often face difficult decisions about whether to bring up their child as a boy or a girl. Some researchers now say that as many as 1 person in 100 has some form of DSD.

When genetics is taken into consideration, the boundary between the sexes becomes even blurrier. new technologies in DNA sequencing and cell biology are revealing that almost everyone is, to varying degrees, a patchwork of genetically distinct cells, some with a sex that might not match that of the rest of their body. Some studies even suggest that the sex of each cell drives its behaviour, through a complicated network of molecular interactions.

These discoveries do not sit well in a world in which sex is still defined in binary terms. Few legal systems allow for any ambiguity in biological sex, and a person's legal rights and social status can be heavily influenced by whether their birth certificate says male or female.

That the two sexes are physically different is obvious, but at the start of life, it is not. Five weeks into development, a human embryo has the potential to form both male and female anatomy. 

For many years, scientists believed that female development was the default programme, and that male development was actively switched on by the presence of a particular gene on the Y chromosome. In 1990, researchers made headlines when they uncovered the identity of this gene which they called SRY. Just by itself, this gene can switch the gonad from ovarian to testicular development. For example, XX individuals who carry a fragment of the Y chromosome that contains SRY develop as males.

By the turn of the millennium, however, the idea of femaleness being a passive default option had been toppled by the discovery of genes that actively promote ovarian development and suppress the testicular programme.

These discoveries have pointed to a complex process of sex determination, in which the identity of the gonad emerges from a contest between two opposing networks of gene activity. Changes in the activity or amounts of molecules (such as WNT4) in the networks can tip the balance towards or away from the sex seemingly spelled out by the chromosomes. “It has been, in a sense, a philosophical change in our way of looking at sex; that it's a balance,” 

Studies in mice suggest that the gonad teeters between being male and female throughout life, its identity requiring constant maintenance. In 2009, researchers reported deactivating an ovarian gene called Foxl2 in adult female mice; they found that the granulosa cells that support the development of eggs transformed into Sertoli cells, which support sperm development. Two years later, a separate team showed the opposite: that inactivating a gene called Dmrt1 could turn adult testicular cells into ovarian ones. “That was the big shock, the fact that it was going on post-natally,” says Vincent Harley, a geneticist who studies gonad development at the MIMR-PHI Institute for Medical Research in Melbourne.

Many people never discover their condition unless they seek help for infertility, or discover it through some other brush with medicine. Last year, for example, surgeons reported that they had been operating on a hernia in a man, when they discovered that he had a womb. The man was 70, and had fathered four children.

Studies of DSDs have shown that sex is no simple dichotomy. But things become even more complex when scientists zoom in to look at individual cells. The common assumption that every cell contains the same set of genes is untrue. Some people have mosaicism: they develop from a single fertilized egg but become a patchwork of cells with different genetic make-ups. This can happen when sex chromosomes are doled out unevenly between dividing cells during early embryonic development. 

Biologists may have been building a more nuanced view of sex, but society has yet to catch up. True, more than half a century of activism from members of the lesbian, gay, bisexual and transgender community has softened social attitudes to sexual orientation and gender. Many societies are now comfortable with men and women crossing conventional societal boundaries in their choice of appearance, career and sexual partner. But when it comes to sex, there is still intense social pressure to conform to the binary model.

This pressure has meant that people born with clear DSDs often undergo surgery to 'normalize' their genitals. Such surgery is controversial because it is usually performed on babies, who are too young to consent, and risks assigning a sex at odds with the child's ultimate gender identity — their sense of their own gender. 

In most countries, it is legally impossible to be anything but male or female. Yet if biologists continue to show that sex is a spectrum, then society and state will have to grapple with the consequences, and work out where and how to draw the line. Many transgender and intersex activists dream of a world where a person's sex or gender is irrelevant. Although some governments are moving in this direction, Greenberg is pessimistic about the prospects of realizing this dream — in the United States, at least. “I think to get rid of gender markers altogether or to allow a third, indeterminate marker, is going to be difficult.”

So if the law requires that a person is male or female, should that sex be assigned by anatomy, hormones, cells or chromosomes, and what should be done if they clash? “My feeling is that since there is not one biological parameter that takes over every other parameter, at the end of the day, gender identity seems to be the most reasonable parameter,” says Vilain. In other words, if you want to know whether someone is male or female, it may be best just to ask.

http://www.nature.com/news/sex-redefined-1.16943


http://en.wikipedia.org/wiki/Sex
http://en.wikipedia.org/wiki/Intersex
http://en.wikipedia.org/wiki/Disorders_of_sex_development
http://en.wikipedia.org/wiki/Gender
http://en.wikipedia.org/wiki/Gender_identity
http://en.wikipedia.org/wiki/Gender_role
http://en.wikipedia.org/wiki/Androgyny
http://en.wikipedia.org/wiki/Third_gender

photo; Andreja Pejić

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