Genetics & Molecular Biology
“If you want to be happy for the rest of your life you need to make an ugly woman your wife,” or “if your rent is late and you might have to litigate, don’t worry, be happy,” are a few of the ways some popular singers verbalize ways to stay happy. The role that genes and environment play on happiness and the choices a person makes in life have been regularly investigated in studies involving criminals and twins.
Common genetic variations affecting nicotine receptors in the nervous system can significantly increase the chance that European Americans who begin smoking by age 17 will struggle with lifelong nicotine addiction, according to researchers at the University of Utah and their colleagues at University of Wisconsin-Madison.
The study highlights the importance of public health efforts to reduce the number of youth who begin smoking.
These common gene variations - single nucleotide polymorphisms (SNPs) - are changes in a single unit of DNA. SNPs that are linked and inherited together are called a haplotype. The researchers found that one haplotype for the nicotine receptor put European American smokers at greater risk of heavy nicotine dependence as adults, but only if they began daily smoking before the age of 17. A second haplotype actually reduced the risk of adult heavy nicotine dependence for people who began smoking in their youth.
One of the many aggravations I encounter when reviewing manuscripts is that some authors greatly overstate the applicability of statistically significant patterns they report. For example, a statistically significant pattern in a small comparison of a few animals may be extrapolated in the discussion to the kingdom at large.
Today I was disappointed to see a paper that is soon to come out in Zoology that does the opposite -- i.e. takes a non-significant relationship in a handful of species and pretends that it challenges the importance of broad relationships that have been considered important for decades.
The paper in question is:
Epigenetic mechanisms are at the heart of developmental biology, orchestrating the formation of many different tissues and organs from a fertilised egg. Almost all cells in an individual have exactly the same genetic material, yet behave very differently depending on which organs they comprise. Epigenetic regulation enables the fine-tuning of our genes and their expression in different places at different times, leading to the amazing complexity we see in humans despite the relatively small number of unique genes.
We all get two copies of every gene, one from our mother and one from our father. In many cases both copies are used or 'expressed’, however it is becoming clear that for some genes either the mother’s or the father’s version is used preferentially, a phenomenon known as genomic imprinting.
Specific chemical modifications to the DNA, such as methylation, appear to give the chromosomes a ‘memory’ as to their parental origin. These ‘epigenetic’ imprints, from the Greek meaning ‘on top of’, modify the structure of the DNA but not its sequence. In addition to parental modifications, it is thought that epigenetic changes may also arise in response to environmental factors, enabling an organism's genes to adapt and respond differently, even though the gene sequence does not change.
In general, domesticated food plants have larger fruits, heads of grain, tubers, etc, because this is one of the characteristics that early hunter-gatherers chose when foraging for food and later planting it.
Domesticated tomatoes can be up to 1000 times larger than their wild relatives but how did they get so big? While tomatoes have long been bred for shape, texture, flavor and nutrient composition, but it has been difficult to study these traits in tomatoes, because many of them are the result of many genes acting together.
These genes are often located in close proximity on chromosomal regions called loci, and regions with groups of genes that influence a particular trait are called quantitative trait loci (QTLs). When a trait is influenced by one gene, it is much simpler to study, but quantitative traits, like skin and eye color in humans or fruit size in tomatoes, cannot be easily defined just by crossing different individuals.
What makes a pointer point, a sheep dog herd, and a retriever retrieve? Why do Yorkshire terriers live longer than Great Danes? And how can a tiny Chihuahua possibly be related to a Great Dane?
Dogs vary in size, shape, color, coat length and behavior more than any other animal and until now, this variance has largely been unexplained. Now, scientists have developed a method to identify the genetic basis for this diversity that may have far-reaching benefits for dogs and their owners.
In the cover story of Genetics, research reveals locations in a dog's DNA that contain genes that scientists believe contribute to differences in body and skull shape, weight, fur color and length – and possibly even behavior, trainability and longevity.
In biology, everything has a history. Creationists love to try to calculate the probability of a new gene spontaneously coming into existence, but that's not how genes are born. New genes most often come from other genes: one gene gets duplicated by a freak accident (like the accidental duplication of a chunk of chromosome, a whole chromosome, or even an entire genome), so that you suddenly have a cell with two working copies of the same gene. As time goes on (that is, time on an evolutionary scale), those two duplicate genes start to divide up the work that was originally done by just one gene. One copy might end up specializing in one particular task, picking up mutations along the way that gradually transform this copy into an independent gene in its own right, with its own specialized function. From one gene, you get two, each with a distinct role in the cell.
It sounds like a nice evolutionary story, but do scientists have any real examples of duplicate genes evolving new functions?
Scientists have been trying to understand how and when we gain or lose fat cells, and now a paper in this week's issue of Nature
reports that nuclear bombs are the key to solving this problem.
To understand how our bodies regulate our weight, researchers are interested in knowing how the number of fat cells changes over our lifetime - do we stop making more fat cells after adolescence? Do we keep the same fat cells all of our adult lives, or do some die off and get replaced by new ones? The typical way to study the birth and death of cells in live animals is to use radioactive tracers that label DNA, but these experiments are too toxic to try in humans. It turns out though, that the US and Soviet militaries did the experiment for us, with above-ground nuclear bomb tests in the late 1950's, tests which spewed large amounts of radioactive carbon in the atmosphere. That radioactive carbon is now in our DNA (at least for those of us alive during the cold war), and it provides a convenient "manufactured on" date for our long-lived fat cells.
Much of the coverage of autism in the media focuses on the arguments of advocates, scientists, and government officials over the relationship between vaccines and autism. But out of the spotlight, a bigger story is brewing: the hunt for autism genes, a technically difficult hunt which is pressing forward using all of the tools modern genetics has to offer. If you are like me, news stories about autism have left you with only a vague impression of the current scientific state of understanding, the impression that researchers strongly deny any link between autism and vaccines, but have little else to say about what the real cause of autism might be.
If that is your impression, you'll perhaps be surprised to learn that roughly 20% of autism cases in the US are linked to known genetic changes, a minor fraction of autism cases to be sure, but much higher than I would have guessed. That autism has a genetic basis is a well-established finding, and while this by no means rules out environmental factors, genetics is at the core of the recent progress scientists have made in understanding autism. The genetics of autism, however, is not simple - no surprise, since autism involves our most complex organ, the brain, in one of its most complex functions, social interaction. Untangling the genetic and environmental factors that underlie autism will be tough, but in the process we will learn more about how many different genes work together in a child to control the developing brain.
In 2001, the DNA sequence was published of a combination of persons. The DNA sequences of Jim Watson, discoverer of the DNA’s double helix structure, followed in 2007, and later the DNA of gene hunter Craig Venter. Recently the completion of the sequences of two Yoruba Africans was announced.
Now geneticists of Leiden University Medical Centre (LUMC) in The Netherlands have determined the first DNA sequence of a woman - and also the first European. This has been announced by the researchers this morning, during a special press conference at ‘Bessensap’, a yearly meeting of scientists and the press in the Netherlands.
Following in-depth analysis, the sequence will be made public, except incidental privacy-sensitive findings. The results will contribute to insights into human genetic diversity.
Who is Marjolein Kriek?