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Erin Hamson

MIT OpenCourseWare | Biology | 7.012 Introduction to Biology, Fall 2004 | Video Lecture... - 0 views

ocw.mit.edu/...embed32

evolution mit science

shared by Erin Hamson on 18 Oct 10 - No Cached
  • And what this means is that if you look at a pedigree like this, and for example, here we have a mother and a father, girls are always round, boys are square. And here you'll see the mitochondrial DNA, it's donated to all of the children, but the fact is that these boys, when they mate, when they have offspring, they will no longer pass along her mitochondrial DNA, so it will be lost. And the only way the mitochondrial DNA can be transmitted is through one of her daughters, who in turn, have daughters.
  • Here's some other interesting principles. Mitochondrial DNA passes always from the mother, so when a fertilized egg is formed, Dad gives his chromosomes, but he doesn't donate for any, doesn't donate any mitochondrial DNA.
  • animals are related to one another. This is kind of a fun undertaking. Look at this. Why is it fun? Well it's, it's kind of an amusing idea, how often were cows domesticated during the history of humanity? How often were sheep domesticated? Pigs, water buffalos, and horses. And what you see here is that cattle were domesticated on two occasions, probably once in Western Asia, the middle east, and once in Eastern Asia. Sheep were domesticated twice, all modern sheep following these two families here
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  • And that is, certain genes can evolve progressively over a long period of time, because they don't encode vital functions, or they may even be sequences between genes that don't encode phenotype at all. Imagine, for example, we have a situation were here we have a gene which encodes a vital function, like the eye, here's another gene that encodes another function, oh I don't know, a leg. And here we have intergenic sequences. After all, as you have learned by now, more than 96% of the DNA in our genome, doesn't encode proteins, and probably isn't even responsible for regulating genes. So these sequences, right in here, can mutate freely during the course of evolution, without having a deleterious effect on the phenotype of the organism. There's no evolutionary pressure to constrain the evolution of these genes
  • And many of these neutral mutations, which have no effect on organismic fitness, but are simply evolutionary neutral, are sometimes called polymorphisms. The term polymorphism, -morph is once again morphology, derives from the fact that species tend to be polymorphic, we don't all have blond hair, we don't all have brown eyes.
  • If you look at two chimpanzees living on opposite sides of the same hill in West Africa, they are genetically far more distantly related to one another, than any one of us, by a factor of 10 to 15. Two chimpanzees, they look exactly the same, they have the same peculiar habits, but they're genetically far more distantly-related than we are to one-another, than I am to any one of you, or than any one of you is to one another. And what does that mean? It means that, roughly speaking, the species of chimpanzees is, at least, 10 or 15 times older than our species are. We're a young species, chimpanzees probably first speciated three or four million years ago, if the paleontological record is, is accurate. Paleontology is the study of old, dusty bones, so you can begin to imagine when chimpanzee bones become recognizable in the earth.
  • And what you see already, in such small populations, is that for example, this male here has two girls, and right away, to the extent he had an interesting Y chromosome, that Y chromosome was lost from the gene pool. This girl, here, had an interesting mitochondrial DNA, but right away that's lost, because she has, she has just two boys. And what you see, in very rapid order, in small populations, there's a homogenization of the genetic compliment, just because the alleles are lost within what's called, genetic drif
  • And if you ask that question, the answer is that we all had a common ancestress who lived about 150,000 years ago. All of us trace our mitochondrial DNA to her. Does that mean that there was only one woman alive there, she's called, Mitochondrial-Eve, again, we don't know her name. Does that mean there was only one woman alive, well it doesn't mean that at all because of what I just told you, in small populations the proto-human population.
  • How much are all of our mitochondrial DNA are related to one another, how distantly related are they to one another, given the rate of evolution of mitochondrial DNA sequences?
  • So where do we all come from, all of us human beings? How closely related are we to one another? Here's, here's a measurement of the distances between different mitochondrial DNA's from different branches of humanity. And what you see is something really quite extraordinary and stunning. Here, you'll see that the people, the non-African lineages here and here, are actually relatively closely related to one another.
  • And by the way, all the genes that are present here, the alleles that are present here, can also be found in Africa, but in relatively small proportions in Africa
    • Erin Hamson
      Erin Hamson on 18 Oct 10
       
      Suggesting that all people came from Africa
  • So, what happens there, that's a testimonial to the tragic fate of the Indians, where the conquistadors from Spain came in, killed all the men, and took all the women, to be their brides. How else can you explain the fact that there's no Indian Y chromosomes, there's all, there is instead only European Y chromosomes.
  • When you do genetic counseling of family these days, one of the strictures is, that you never tell the family if the children have genetic polymorphisms that don't match that of the person whom they think is their father. They don't look like their, the person whom they regard as father, but that's always assumed to be a role of the genetic dice.
  • Here's a fun story I like to tell each year, and it's about the Cohen and Y chromosome, and you'll see what an amusing story this is, just from genetics. Now the name Cohen, in Hebrew means, a high priest, and you've heard people named Cohen, it's not such an uncommon name among the Jews. And it says, in the Bible, in Genesis and Exodus, that all the high priests in the Bible are the descendants of Aaron, the brother of Moses.
  • hen it should be the case that all male Cohen's should have the same Y chromosome, right?
  • Because keep in mind, any single affair with the milkman or the mailman, over 3,000 years, would've broke this chain of inheritance, any single incidence of non-paternity. It's a really astounding story, and it's hard, there can be no artifact to it, there's no bias in it, there's no other way to explain it.
  • And what they found was that all members of the, almost all members of the ruling cast among the Lembas, had the same Y chromosome, and the Y chromosome had exactly the same polymorphisms of the Cohen Y chromosome
  • What I'm telling you is that these two genes are totally interchangeable, that they are effectively indistinguishable from one another, functionally they have some sequence relatedness, but in terms of the way they program development, they are effectively equivalent. And what this means is that the progenitor of these two genes must've already existed at the time that the flies and we diverged, which six or seven-hundred million years ago, and in the intervening six or seven-hundred million years, these genes have been totally unchanged.
  • once the gene was developed, evolution could not tinker with it, and begin to change it in different ways, ostensibly because such tinkering would render these genes dysfunctional, and thereby would inactivate them, thereby depriving the organism of a critical sensory organ.
  • Erin Hamson on 18 Oct 10
     
    An excellent discourse on who evolution works, and what it means for us today.
Gideon Burton

Top Internet engineers warn against SOPA - Post Tech - The Washington Post - 0 views

www.washingtonpost.com/...gIQAGRV4vO_blog.html

internet congress government sopa censorship

shared by Gideon Burton on 07 Jan 12 - No Cached
  • When we designed the Internet the first time, our priorities were reliability, robustness and minimizing central points of failure or control. We are alarmed that Congress is so close to mandating censorship-compliance as a design requirement for new Internet innovations. This can only damage the security of the network, and give authoritarian governments more power over what their citizens can read and publish. The US government has regularly claimed that it supports a free and open Internet, both domestically and abroad. We cannot have a free and open Internet unless its naming and routing systems sit above the political concerns and objectives of any one government or industry. To date, the leading role the US has played in this infrastructure has been fairly uncontroversial because America is seen as a trustworthy arbiter and a neutral bastion of free expression. If the US begins to use its central position in the network for censorship that advances its political and economic agenda, the consequences will be far-reaching and destructive.
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