Cosma has to go and show off with a magisterial demonstration of why he is the smartest man on the internet: he’s written an exceptionally thorough description of heritability and IQ. It’s not a light read (statistics and genetics!), but it’s probably the most informative thing I’ve read in a month or more.
I’m sure I’m going to have to read it a few more times before I’ve absorbed it all.
The Hox genes are a set of transcription factors that exhibit an unusual property: they provide a glimpse of one way that gene expression is translated into metazoan morphology. For the most part, the genome seems to be a welter of various genes scattered about almost randomly, with no order present in their arrangement on a chromosome — the order only becomes apparent in their expression through the process of development. The Hox genes, on the other hand, seem like an island of comprehensible structure. These are all genes that specify segment identity — whether a segment of the embryo should form part of the head, thorax, or abdomen, for instance — and they’re all clustered together in one (usually) tidy spot.
Within that cluster, we see further evidence of order. Look at just the Drosophila part of the diagram below: there are 8 Hox genes in a row, and their order within that row reflects the order of expression in the fly body. On the left or 3′ end of the DNA strand, lab (labial) is expressed in the head, while Abd-B (Abdominal-B) is expressed at the end of the abdomen.
Knocking out individual Hox genes in the fly causes homeotic transformations — one body part develops into another. These genes are early actors in the cascade of interactions that enable the development of morphologically distinct regions in a segmented animal — the activation of a Hox gene from the 3′ end is one of the earliest triggers that leads the segment to develop into part of the head.
Now look at the mouse part of the diagram above. We vertebrates have Hox genes that are homologous to the fly Hox genes, and they’re also clustered in discrete locations with 3’→5′ order reflecting anterior→posterior order of expression. There are differences — the two most obvious that we have more Hox genes on the 5′ side (these correspond to expression in the tail—flies do not have anything homologous to the chordate tail), and vertebrates also have four banks of Hox genes, HoxA, HoxB, HoxC, and HoxD. This complicates matters. Vertebrates have these parallel, overlapping sets of Hox genes, which suggests that morphology could be a product of a combinatorial expression of the genes in the four Hox clusters: there could be a Hox code, where identity can be defined with more gradations by mixing up the bounds of expression of each of the genes.
Greg Laden has an excellent article on the genetics and evolution of race — basically, it’s an irrelevant pairing of concepts.
“Eat your heart out, Philip Rushton,” indeed.
I got some email today with lots of constructive suggestions (See? Not all my email is evil!) for how we ought to change the education of biology students — such as by giving them a foundation in the history and philosophy of our science, using creationist arguments as bad examples so the students can see the errors for themselves, etc. — and it was absolutely brilliant, even the parts where he disagreed with some things I’d written before. Best email ever!
Of course, what helped is that I spent my summer “vacation” putting together a new freshman first semester course for biology majors that I’m teaching for the first time right now, and it’s exactly the course he described. It was eerie, like one of my future students had invented a time machine and come back into the past to tell me what to do. A lot of the course content is locked up behind a password-protected firewall, I’m afraid, but just to show you what I’m talking about, I’ll put the course schedule below the fold.
If it existed, it might also be profoundly autistic and … diabetic? So science cannot disprove the existence of a soul, but one thing we’re learning is how much valued human properties such as love and attachment and awareness of others are a product of our biology — emotions like love are an outcome of chemistry, and can’t be separated from our meaty natures.
The latest issue of BioEssays has an excellent review of the role of the hormone oxytocin in regulating behaviors. It highlights how much biochemistry is a determinant of what we regard as virtues.
Abbie of ERV has made her first guest post on the Panda’s Thumb, and it’s a good one. Go see how Behe was wrong and there are documented genetic and biochemical changes in the evolution of HIV, including the evolution of new molecular machinery.
We now have a draft of the sea anemone genome, and it is revealing tantalizing details of metazoan evolution. The subject is the starlet anemone, Nematostella vectensis, a beautiful little animal that is also an up-and-coming star of developmental biology research.
A most important reason for this work is that the anemone Nematostella is a distant relative of many of the animals that have already been sequenced, and so provides an essential perspective on the evolutionary changes that we observe in those other organisms. Comparison of its genome with that of other metazoans is helping us decipher the likely genetic organization of the last common ancestor of all animals.
She’s fired up the The Sixth International again, and she threatens promises to be at it for a long, long, long time—she bears a longevity mutation, a single nucleotide substitution in the mitochondrial genome associated with some long-lived people. And some people claim there is no such thing as a beneficial mutation…
Anyway, it’s personally interesting that it’s mitochondrial—that means it is passed down through the maternal line. Since my father’s side of the family is grievously short-lived, but my mother’s side keeps going for nearly forever, that’s good news, if the maternal secret is particularly robust mitochondria. Since this particular allele appears in various lines all around the world, there’s a slim chance.
Otherwise, I’m afraid my only mutant power seems to be the ability to dissolve chewing gum. I was ripped off.
The general pattern of developing positional information in Drosophila starts out relatively simply and gets increasingly complicated as time goes by. Initially, there is a very broad distribution of a gradient of a maternal morphogen. That morphogen then triggers the expression of narrower (but still fairly broad) bands of aperiodic gap genes. The next step in this process is to turn on sets of genes in narrow, periodic bands that correspond to body segments. This next set of genes are called the pair-rule genes, because they do something surprising and rather neat: they are turned on in precisely alternating bands. In the picture above, for instance, one pair-rule gene, even-skipped, has been stained blue, and it is expressed in parasegment* 1, 3, 5, 7, etc. Another, fushi tarazu, has been stained brown, and this gene is turned on in parasegments 2, 4, 6, 8, etc.
There are a couple of small towns on the border between Utah and Arizona that are basically feudal theocracies, ruled by a particularly nasty splinter sect of polygamist Mormons. It’s got some truly ugly social consequences — daughters are prizes given away to church leaders, while sons are competitors who are driven away — but now it turns out that there also some biological consequences. The community is deeply inbred, and their prize is the possession of the highest rate of fumarase deficiency in the world, with at least 20 afflicted children in the last 15 years. Fumarase is an enzyme in the Krebs cycle; deleterious mutations in these genes cause a metabolic disorder called fumarase deficiency.
It’s not a nice innocuous disease. It’s variable in its severity, but bad cases lead to debilitating mental retardation, frequent seizures, characteristic appearance (a large head, coarse features), and death. With care, affected individuals can live for many years, but they’ll never be self-sufficient and they do require near-constant attention.
And because it is widespread in a small isolated community, that for various reasons (including religion) is neither a desirable destination for new residents nor will its population try to integrate with the outside world, it’s going to get worse. Half the children born to a pair of carriers will be carriers of the disease themselves, and those nice big Mormon families produce lots of children. Not only are the young girls in this community forced to marry and start spawning baby after baby, but compound the horror with the idea that some will be having children who will need to have their diapers changed for 20 years…
