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Parlons Futur 12/11/2019 : Comment la génétique moderne va bientôt permettre de choisir la taille de ses enfants (et autres critères polémiques) ; les immeubles en bois à la rescousse du climat

Le début de la newsletter à retrouver ici.

Voici les 2 news dont vous trouverez le résumé au format bullet points plus bas :

  • Comment la génétique moderne va bientôt permettre de choisir la taille de ses enfants (et autres critères polémiques)
  • Les immeubles en bois à la rescousse du climat
Comment la génétique moderne va bientôt permettre de choisir la taille de ses enfants (et autres critères polémiques) (The Economist)
  • En bref : beaucoup plus de conditions et dispositions sont héréditaires qu'on ne le pense, et la plupart ne dépendent pas que d'un gène, mais de plusieurs. Si on sait depuis quelque temps identifier une condition qui ne dépend que d'un gène, on est en passe de pouvoir aussi le faire pour ces conditions qui dépendent de nombreux gènes variant parfois d'un simple nucléotide (une des quatre lettres de l'ADN : A, T, G, C). Et si suffisamment d'embryons d'un couple sont générés (par fécondation in vitro), on va donc pouvoir choisir d'implanter celui qui a le plus de chances de posséder les traits désirés par les parents. La société Genomic Prediction est en pointe dans le domaine et propose déjà des tests pour certaines conditions.
  • Voici quelques dispositions qui sont en partie héritées des parents (et non seulement dues à la socialisation) :
    • A heritability of 100% indicates that any differences in a trait between individuals in that population are accounted for solely by genetic factors, while 0% suggests the environment alone is responsible.
      • An analysis published in 2015 of more than 2,700 studies of heritability shows :
      • that physical traits like susceptibility to heart disease : 44% of heritability
      • eye disorders (71%),
      • mental traits, including “higher-level” cognitive functions (47%) such as problem-solving and abstract thought.(also known as intelligence)
    • In 1990, a study led by Robert Plomin, now at King’s College, London, compared the habits of adopted children with those of their birth mothers.
      • It found television-watching has a heritability of about 45%.
      • Similar surprisingly heritable traits include a child’s tendency to be bullied at school (more than 70%)
      • child’s tendency to be accident-prone (51%).
      • someone’s likelihood of being religious (30-40%)
      • someone’s likelihood or of getting divorced (13%) is heritable.
  • pre-implantation testing of human embryo is already used in some places, in cases where there is a chance of parents passing on a condition, such as Tay-Sachs disease, that is caused by a single faulty gene.
  • The company Genomic Prediction is, however, offering something more wide-ranging. It is screening embryos for almost 1 million single-nucleotide polymorphisms (SNPs).
    • single-nucleotide polymorphisms (SNPs) are places where individual genomes routinely differ from one another at the level of an individual genetic letter.
  • Individual SNP differences between people rarely have much effect. But add them up and they can raise or lower by quite a lot the likelihood of someone suffering a particular disease. Generate several embryos and SNP-test them, then, and you can pick out those that you think will grow up to be the healthiest
  • Though human beings are genetically more than 99.9% alike, they have 6 billion genetic letters in their genomes. This is where the SNPs are hidden, for a diversity of less than 0.1% still leaves room for millions of them.
  • And when SNPs’ contributions are combined, their effects can be significant.
  • For height, for example, the number of relevant SNPs is reckoned to be about 100,000—each adding or subtracting, on average, 0.14mm to or from a person’s adult stature.
  • Furthermore, most of these SNPs are in parts of the genome that do not encode proteins at all. Rather, they regulate the activities of other genes and often have no obvious connection to the trait in question. (a trait : une caractéristique considérée, comme la taille par ex.)
    • En effet, on pense souvent que les gènes servent seulement ou principalement à coder pour les protéines qui constituent notre corps et assurent son bon fonctionnement, mais que nenni! : protein-coding genes make up only about 2% of a person’s DNA.
  • A combination of SNP arrays (éventail de SNP connues), larger samples of volunteers and better computing methods means it is now possible to find millions of variants that contribute to a trait. An individual’s score from these variants, known as his polygenic score, can then be calculated by adding up their contributions to give, for example, his risk of developing a particular disease in later life.
  • Using these and similar studies, it is possible to draw up lifetime risk profiles for various medical conditions.
  • Genomic Prediction thus says it is able to offer couples undergoing IVF (In Vitro Fertilization) a polygenic risk score for each embryo for a variety of diseases including type 1 diabetes, type 2 diabetes, breast cancer, testicular cancer, prostate cancer, basal-cell carcinoma, malignant melanoma, heart attack, atrial fibrillation, coronary artery disease, hypertension and high cholesterol. At the moment it does not offer scores for non-medical traits like height or educational attainment. But there is nothing to prevent it from doing so should it so wish.
  • Even for medically relevant scores, however, some worry about this approach. One concern is pleiotropy—the phenomenon of the same piece of DNA influencing several apparently unrelated traits. Choosing an embryo with a low risk of heart disease might accidentally give it, say, a higher chance of developing epilepsy. Single-mindedly maximising scores for positive traits like intelligence or height may therefore increase the risk of genetic disorders.
  • Dr Hsu, who in 2014 predicted that reproductive technologies would soon be used to select for more intelligent offspring, estimates that an IQ gain of between 10 and 15 points would be possible if couples were allowed to choose between ten embryos
  • This is plausible. Before 2008, when the first snp chips for cattle became available, the annual milk yield of dairy cows in America had been increasing at about 50kg per year. After six years of chip-based polygenic selection, the rate of increase had doubled to more than 100kg per year. This suggests the technique is powerful—in cattle at least. Despite Dr Hsu’s optimism, however, pleiotropism has reared its head in these animals. They have become less fertile and have weaker immune systems.
  • In Norway, for example, heritability of educational attainment increased after the second world war as access to education widened. Since all children now had more or less the same opportunities at school, environmental variation was largely ironed out and the effects of genetic differences consequently exaggerated.
  • In the end, then, it is generally a good idea to remember that human beings have already been optimised by a powerful agent called natural selection. Trade-offs between different pieces of physiology, even in domestic animals, will have been forged in the crucible of evolution and will generally be optimal, or close to it. Genetic tinkering may sometimes improve things. But by no means always
L'ingrédient inattendu pour "verdir" la construction et la vie des immeubles : le bois! (The Economist)
  • From January 1st 2019 all new public-sector buildings in the European Union must be built to “nearly zero-energy” standards. All other types of buildings will follow in January 2021.
  • These standards are less green than they seem. Wind turbines and solar panels on top of buildings look good but are much less productive than wind and solar farms. And the standards only count the emissions from running a building, not those belched out when it was made. Those are thought to account for between 30% and 60% of the total over a structure’s lifetime.
  • The International Energy Agency (IEA), a research group, estimates that putting up and running buildings consumes 36% of the world’s energy and produces some 40% of energy-related carbon emissions. 83% of that energy is used to light, heat, cool and run appliances.
  • Consider the energy that goes into producing construction materials and the share of emissions from buildings is even higher. More than 5bn tonnes of cement—the raw material for concrete and mortar—is produced each year, adding a further 6% of emissions. The steel industry, 50% of whose production goes into construction, accounts for another 8%
  • They can use more recycled steel and can be prefabricated in off-site factories, greatly reducing lorry journeys. But no other building material has environmental credentials as exciting and overlooked as wood.
  • The energy required to produce a laminated wooden beam (poutre) is 17% of that required for a steel one of comparable strength.
  • As trees take carbon out of the atmosphere when growing, wooden buildings contribute to negative emissions by storing the stuff. When a mature tree is cut down, a new one can be planted to replace it, capturing more carbon.
  • After buildings are demolished, old beams and panels are easy to recycle into new structures.
  • And for retrofitting older buildings to be more energy efficient, wood is a good insulator. A softwood window frame provides nearly 400 times as much insulation as a plain steel one of the same thickness and over a thousand times as much as an aluminium equivalent.
  • In March 2019 the world’s tallest wooden skyscraper, 85 metres high (18 floors), opened in Norwway (pic above)
  • The surprise is that all of its supporting columns are made of glulam—wooden beams laminated together. Most of the wood came from sawmills and spruce forests within a 50km radius of the tower, says Rune Abrahamsen, chief executive of Moelven, the Norwegian firm that supplied it.
  • wood does not melt in a fire. And once it has charred it does not continue burning, like a flamed-out log fire. The fire-exit staircase of the now tallest wooden building in the world is clad in cross-laminated timber, a material widely regarded as safer than steel in a blaze.
  • because wood is so light compared with steel, brick or concrete, it lends itself to the mass production of buildings in factories. That should cut emissions from moving materials to building sites.
  • Some buildings can now produce more renewable electricity than they use, which helps to offset the emissions used in their construction. Norway is a pioneer. The Powerhouse in central Trondheim produces 49 kWh of energy/m2 of floor space per year from solar panels and consumes just 21—an impressive achievement for a building just 350km from the Arctic Circle.
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