genetics
clock | January 1, 2007Food From Cloned Animals Safe? FDA Says Yes, But Asks Suppliers To Hold Off For Now:
The U.S. Food and Drug Administration (FDA) has issued three documents on the safety of animal cloning -- a draft risk assessment; a proposed risk management plan; and a draft guidance for industry.
The draft risk assessment finds that meat and milk from clones of adult cattle, pigs and goats, and their offspring, are as safe to eat as food from conventionally bred animals. The assessment was peer-reviewed by a group of independent scientific experts in cloning and animal health. They agreed with the methods…
razib | December 31, 2006Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians:
...these results point to the importance of several genes in shaping the pigmentation phenotype and a complex evolutionary history involving strong selection. Polymorphisms in two genes, ASIP and OCA2, may play a shared role in shaping light and dark pigmentation across the globe while SLC24A5, MATP, and TYR have a predominant role in the evolution of light skin in Europeans but not in East Asians. These findings support a case for the recent convergent evolution of a lighter pigmentation phenotype in…
razib | December 29, 2006Earlier this week I sketched out the general theoretical basis for not denying unexpected deviations from expectation, so to speak, when it comes to quantitatve traits. The main issue is that varying genetic backgrounds leave unaccounted for gene-gene interactions, and so our predictions when two populations are crossed maybe confounded (within a population ceteris paribus is far more likely to hold). In any case, I thought I'd give you two obvious examples from humans.
First, in 2005 Helgadottir et. al. found that African Americans are at greater risk for myocardial infarction vis-a-vis…
razib | December 28, 2006Life has been occupying me, why, between good wine (I prefer mild Chardonnay), work, books and beautiful women who detest science fiction I haven't been able to resume my survey of Evolutionary Genetics: Concepts & Case Studies. Nevertheless, I'd like to point you to Jason Rosenhouse's Evolution Blog which has been putting the Science in ScienceBlogs. I especially enjoyed Chance, Stochasticity, Probability and Evolution, though I am of the opinion that these sort of disagreements are often more semantical than substantial. Terms like "adaptationism" and "punctuated equilibria" allude…
clock | December 27, 2006Perhaps. But we do other stuff just like chicken (December 09, 2004):
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Fantastic news in science:
Researchers compare chicken, human genomes
http://www.eurekalert.org/pub_releases/2004-12/nhgr-rcc120804.php
Some highlights:
Chicks have less junk DNA:
In their paper published in Nature, members of the International Chicken Genome
Sequencing Consortium report that the chicken genome contains significantly less
DNA than the human genome, but approximately the same number of genes.
Researchers estimate that the chicken has about 20,000-23,000…
razib | December 26, 2006A few months ago I posted Discrete continuity in genetics to show how the granular nature of genetic inheritance may still manifest to our perception as continuous variation (i.e., quantitative traits). I used skin color as a model trait because it is easy to relate to, and we are beginning to understand its genetics in detail as I write. To recap, it seems that 3-5 genetic loci control more than 90% of the intergroup variation across populations in complexion. That is, you have a small number of genes which generate the range between black and white skin. These genes come in various flavors…
razib | December 22, 2006New paper in PLOS Genetics, Low Levels of Genetic Divergence across Geographically and Linguistically Diverse Populations from India. Here's the conclusion:
Populations from India, and groups from South Asia more generally, form a genetic cluster, so that individuals placed within this cluster are more genetically similar to each other than to individuals outside the cluster. However, the amount of genetic differentiation among Indian populations is relatively small. The authors conclude that genetic variation in India is distinctive with respect to the rest of the world, but that the level…
evolgen | December 21, 2006There's an interesting discussion going on at Pharyngula regarding virgin birth in Bethlehem Komodo dragons. Two captive females in Europe recently gave birth to clutches of eggs despite no to minimal contact with males. The progeny are all homozygous at the each of the seven loci surveyed, with alleles matching those of the mothers. The logical conclusion to be drawn is that the eggs arose via parthenogenesis -- either by reabsorption of the second polar body or suppression of the second meiotic division.
Take note that this is not clonal reproduction -- the progeny contain two copies of…
pharyngula | December 21, 2006
I've just read the article on the parthenogenetic Komodo dragons in Nature, and it's very cool. They've analyzed the genetics of the eggs that have failed to develop (the remainder are expected to hatch in January) and determined that they were definitely produced without the aid of a male.
We analysed the parentage of the eggs and offspring by genetic fingerprinting. In the clutches of both females, we found that all offspring produced in the absence of males were parthenogens: the overall combined clutch genotype reconstructed that of their mother exactly. Although all offspring were…
razib | December 18, 2006About a month ago I posted quite a bit about Neandertal introgression into modern humans. That is, the uptake of Neandertal alleles are a few specific adaptively salient loci even while ancestry remains predominantly African. Now John Hawks and Gregory Cochran have a new paper out, Dynamics of Adaptive Introgression from Archaic to Modern Humans, which synthesizes the first of the new results. The paper is open access, but I'll throw out the money shot:
We suggest that adaptive introgression of alleles from archaic humans may be one of the central mechanisms leading to the "human revolution…
razib | December 17, 2006Here is a summary of findings by a paper which suggests that the vast majority of genetic counselors tend to err on the side of protecting a mother's privacy if her husband is not the father of her child. Here is an important point though:
It is much more likely that bringing up the possibility prior to testing will put the woman in the very position we are trying to protect her from. ... If, as I have suggested, the counselor plans to attempt to keep paternity but not personal genetic information from the man, it is probably better not the discuss the issue ahead of time.
The problem is…
razib | December 14, 2006P-eter comments on the Pakistani family which can't feel pain. I remember in a genetics course once seeing the professor chart out a pedigree and calculate inbreeding coefficients and the expectation of the unmasking of deleterious alleles given certain matings. Now and then we would laugh nervously since of course real matings between individuals so closely related would be creepy and unethical...but Pakistan with its culture of cousin-loving down the generations1 makes the science possible in real life! Let a thousand deleterious recessives bloom across the landscape!
1 - Remember that…
clock | December 12, 2006Scientists building a better mosquito:
Without mosquitoes, epidemics of dengue fever and malaria could not plague this planet.
The skin-piercing insects infect one person after another while dining on a favorite meal: human blood.
Eliminating the pests appears impossible. But scientists are attempting to re-engineer them so they cannot carry disease. If they manage that, they must create enough mutants to mate with wild insects and one day to outnumber them.
Researchers chasing this dream, including an N.C. State University entomologist, know they may court controversy. Genetically modified…
razib | December 12, 2006The story of lactose tolerance evolving multiple times has blown up a bit, thanks to Nick Wade at The New York Times. Some people are making analogies to light skin evolving via different genetic architectures (remember, skin color is a polygenic trait, albeit dispersed over ~4 loci of large effect). But there is a difference, light skin color emerges via loss of functionality or expression on the loci which result in pigment production. There are many ways to lose function, but it generally is considered more difficult to gain function. And yet this is what lactose tolerance is. Or is it…
razib | December 11, 2006Convergent adaptation of human lactase persistence in Africa and Europe:
A SNP in the gene encoding lactase (LCT) (C/T-13910) is associated with the ability to digest milk as adults (lactase persistence) in Europeans, but the genetic basis of lactase persistence in Africans was previously unknown. We conducted a genotype-phenotype association study in 470 Tanzanians, Kenyans and Sudanese and identified three SNPs (G/C-14010, T/G-13915 and C/G-13907) that are associated with lactase persistence and that have derived alleles that significantly enhance transcription from the LCT promoter in…
purepedantry | December 7, 2006Your gut reaction is probably that the question is irrelevant; what parent would choose for their child to have a genetic disease. That was my reaction.
Apparently, however, some parents with genetic diseases that make them lead relatively normal lives but isolate them into special social groups -- such as deafness or dwarfism -- are electing for their children to also have these genetic diseases. As reported in the NYTimes:
Wanting to have children who follow in one's footsteps is an understandable desire. But a coming article in the journal Fertility and Sterility offers a fascinating…
razib | December 6, 2006A few years ago the developmental geneticist Armand Leroi burst on to the scene with the engaging book, Mutants, and a controversial op-ed where he attempted to rehabilitate the concept of race. Leroi's op-ed spawned a rebuttal website which brought together a variety of scholars from disparate disciplines to refute his arguments.
Never one to shy away from controversy Armand has published a new essay, The future of neo-eugenics, where he lays out what is happening, and will possibly happen, from the perspective of an evolutionary biologist. The great thing about Armand's work is that he…
evolgen | December 5, 2006A few weeks ago PNAS published a paper on the evolution of snake sex chromosomes. The authors compare snake sex chromosome evolution with that of mammals and birds. Given my passing interest in sex chromosome evolution, I decided to check it out.
Snakes use sex chromosomes to determine the sex of their progeny. Sex in other reptiles, such as crocodiles, is determined by the temperature at which the eggs are incubated. There are two main types of sex chromosome systems in vertebrates: XY and ZW. Most mammals, some fish, some reptiles, and some amphibians use the XY system -- males are…