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Category Archive: Genetics

Jul 22 2014

Biology is a hard problem

New genetic disorders pop up all the time — each one represents a child who may face incredible challenges, or even be doomed to death. A child named Bertrand exhibited some serious symptoms — profound developmental disabilities — shortly after he was born, and no one could figure out what was wrong with him. So …

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Jul 15 2014

The Lyon hypothesis, nicely illustrated

Dang, I teach all this stuff about genes and chromosomes and epigenetics, but I don’t have the advantage of giant floating holographic molecules floating around me. Maybe I’ll have to steal this for my classes. Although it could use some discussion of Blaschko’s lines, to explain why you get a stripey pattern rather than just …

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May 14 2014

#PLOSGenetics: The Case for Junk DNA

This is the paper to read: Palazzo & Gregory’s The Case for Junk DNA. It clearly and logically lays out the complete argument from evidence and theory for the thesis that most of the genome is junk. It’s not revolutionary or radical, though: the whole story is based on very fundamental population genetics and molecular …

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May 11 2014

The hbd delusion

A confession: I have long disliked Nicholas Wade’s science journalism. He has often written about biology in the NY Times, and every time he seems to make a botch of the reporting, because he actually doesn’t understand biology very well. For example, in his very last article for the NYT, he described some work that …

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Apr 08 2014

It worked!

At last I’m home after a long day, but I have good news: my genetics students have been doing a three point mapping cross for the last month or so, which is always worrisome because if they screw it up, you don’t know the results until the very end of the experiment. But now the …

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Mar 11 2014

Pathways to sex

The molecular and genetic events in mammalian sex determination. The bipotential genital ridge is established by genes including Sf1 and Wt1, the early expression of which might also initiate that of Sox9 in both sexes. b-catenin can begin to accumulate as a response to Rspo1–Wnt4 signaling at this stage. In XX supporting cell precursors, b-catenin levels could accumulate sufficiently to repress SOX9 activity, either through direct protein interactions leading to mutual destruction, as seen during cartilage development, or by a direct effect on Sox9 transcription. However, in XY supporting cell precursors, increasing levels of SF1 activate Sry expression and then SRY, together with SF1, boosts Sox9 expression. Once SOX9 levels reach a critical threshold, several positive regulatory loops are initiated, including autoregulation of its own expression and formation of feed-forward loops via FGF9 or PGD2 signaling. If SRY activity is weak, low or late, it fails to boost Sox9 expression before b-catenin levels accumulate sufficiently to shut it down. At later stages, FOXL2 increases, which might help, perhaps in concert with ERs, to maintain granulosa (follicle) cell differentiation by repressing Sox9 expression. In the testis, SOX9 promotes the testis pathway, including Amh activation, and it also probably represses ovarian genes, including Wnt4 and Foxl2. However, any mechanism that increases Sox9 expression sufficiently will trigger Sertoli cell development, even in the absence of SRY.

I was talking about sex and nothing but sex all last week in genetics, which is far less titillating than it sounds. My focus was entirely on operational genetics, that is, how autosomal inheritance vs inheritance of factors on sex chromosomes differ, and I only hinted at how sex is not inherited as a simple …

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Mar 01 2014

Marthe Gautier, another woman scientist trivialized

tri21

I had known that Jérôme Lejeune was the fellow who had discovered that Down Syndrome was caused by trisomy of chromosome 21, but it seems there were many other things about him I had not known — he was just a name. But there were a few things that set me aback. Lejeune became not …

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Feb 14 2014

The state of modern evolutionary theory may not be what you think it is

Selectionist, neutral and nearly neutral theories. a | Selectionist theory: early neo-Darwinian theories assumed that all mutations would affect fitness and, therefore, would be advantageous or deleterious, but not neutral. b | Neutral theory: the neutral theory considered that, for most proteins, neutral mutations exceeded those that were advantageous, but that differences in the relative proportions of neutral sites would influence the rate of molecular evolution (that is, more neutral sites would produce a faster overall rate of change). c | Nearly neutral theory: the fate of mutations with only slight positive or negative effect on fitness will depend on how population size affects the outcome.

I was rather surprised yesterday to see so much negative reaction to my statement that there’s more to evolution than selection, and that random, not selective, changes dominate our history. It was in the context of what should be taught in our public schools, and I almost bought the line that we can only teach …

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Dec 07 2013

The reification of the gene

Razib Khan poked me on twitter yesterday on the topic of David Dobbs’ controversial article, which I’ve already discussed (I liked it). I’m in the minority here; Jerry Coyne has two rebuttals, and Richard Dawkins himself has replied. There has also been a lot of pushback in the comments here. I think they all miss …

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Dec 03 2013

Higher order thinking

The one thing you must read today is David Dobbs’ Die, Selfish Gene, Die. It’s good to see genetic accommodation getting more attention, but I’m already seeing pushback from people who don’t quite get the concept, and think it’s some kind of Lamarckian heresy. It’s maybe a bit much to ask that the gene-centric view …

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