The middle-school introduction to genetics tends to start with Mendel‘s pea experiments and end with Punnet Squares. The focus is on dominant and recessive genes and what’s expressed given various combinations.
Identically Different: Why You Can Change Your Genes by Tim Spector.
However, the way genes behave are not quite that simple. Tim Spector’s new book, Identically Different, goes into the ways that people’s behavior and environment — the things they eat; the chemicals that surround them — affect the way their genes behave. Even identical twins can be profoundly different depending on things that happen in the womb.
Perhaps the most intriguingly argument is that the behavior of grandparents can affect their grandchildren. In the post World War II period in Britain food was scarce, and some people tended to episodes of starvation alternating with binge eating. Spector links this to an increase in the obesity of their grandkids.
The idea that your behavior can affect the expression of your kids’ genes is more akin to Lamark’s view of evolution than Darwin’s.
Puberty starts somewhere in the age range of 8 to 13 years for girls and 9 to 14 years for boys. However, in Norway, in 1850, girls hit puberty at around seventeen. Over the next 100 years that age decreased to thirteen and a half, where it has stabilized, but a similar trend has been seen in pretty much all the industrialized countries, including the U.S.. No one knows quite why, but there are a number of theories, including:
Better nutrition,
increased stress, and
artificial chemicals in the environment or in the diet.
The trend in the timing of puberty in girls (menarche) for four western countries, from 1850 to 1950. Figure via NIH via INSERM.
It seems clear that this trend has something to do with improving living conditions. Rapidly developing countries like China are experiencing the same trend in earlier puberty right now. Wealthier areas in developing countries have girls starting puberty at the same age as girls in “privileged” countries, while their compatriots in the poorer areas do not. Also, Overweight kids tend to start puberty earlier.
However, explaining the earlier puberty is difficult because no one knows for sure what exactly triggers puberty to begin with. The genetic switch that tells the hypothalamus to start the process probably involves multiple genes that are affected in complicated ways by how and where a person grows up (when the environment affects how genes are expressed it’s called epigenetics; NOVA has a nice little program that explains how epigenetics results in differences in identical twins.).
Increased stress might be another explanation. Girls in Bosnia and Croatia started having puberty later and later during the war in the 1990’s. However, it appears that other types of stress, such as from insecure relationships with parents and adoption, can do the opposite and trigger even earlier puberty (note: really early puberty in kids as young as 9 is called precocious puberty and is a growing problem).
Certain artificial chemicals that disrupt the endocrine system, which is responsible for hormone production, have also come under suspicion, but their effects have been hard to prove.
Whatever the reason, the earlier onset of puberty has lead to an increase in the length of adolescence (which tends to start with puberty and ends somewhere in the mid-twenties). It’s hard to say though, if all the extra time is beneficial, since it does give the developing brain extra time to adjust to a more complex society, or if it just makes for a longer period of trying times.
This wonderful, impressionistic image shows representatives of the three domains of life and large viruses, the proposed fourth.
This figure represents the living species in the four small pictures according to the current classification of organisms: eukaryotes (represented by yellow cell), bacteria (represented by green cell), Archaea (represented by blue cell) and viruses (represented by magenta colored Mimivirus).
— Boyer et al. (2010): Boyer M, Madoui M-A, Gimenez G, La Scola B, Raoult D (2010) Phylogenetic and Phyletic Studies of Informational Genes in Genomes Highlight Existence of a 4th Domain of Life Including Giant Viruses. PLoS ONE 5(12): e15530. doi:10.1371/journal.pone.0015530
Carl Zimmer has an excellent piece in Discover Magazine that summarizes the research, and sets out the new tree of life. Particularly important, is the fact that viruses can transfer genes with each other. The other domains tend to mix their genes during reproduction.
Razib Kahn has a fascinating interview with Milford Wolpoff, one of the main scientists behind the research that argues that humans are not all part of a single family tree, descended from a single ancestor who moved out of Africa about 200,000 years ago.
This section focuses on the theory, and has a nice explanation of what mitochondrial DNA is (and why it’s important):
It gives an excellent perspective on how science works, and how scientists work (scientists are people too with all the problems that entails).
The entire thing is a bit dense, but it’s one of the better discussions I’ve seen describing the process of science in action, with little hints at all the challenges that arise from personality conflicts and competing theories.
Color 'fingerprints', with four color standards labeled Y (yellow), R (red), G (green), and B (blue).Gene sequences extracted from sediment in Buzzards Bay, MA, and separated using gel electrophoresis (Image from Ford et al., 1998)
One of the more basic techniques in the microbiologist’s toolkit is gel electrophoresis. It’s used to separate long molecules, like proteins, RNA and DNA from one another. Different organisms have different DNA sequences, so electrophoresis can be used to identify organisms and for DNA fingerprinting. Chromatography is also used to separate different molecules, usually pigments. Therefore, using some filter paper, food coloring, and popsicle sticks I created a nice little chromatographic fingerprinting lab exercise using chromatography as an analogue for electrophoresis.
Food colors and test tubes.
Using a standard set of four food colors (red, blue, green and yellow), I grabbed each students individually and had them add three drops of the colors of their choice to a test tube with 1 ml of water in it. One students went with three straight blue drops, but most picked some mixture of colors. I kept track of the color combinations they used, and labeled their test tube with a unique, random number.
When they’d all created their own “color fingerprint” in the test tubes, I handed them back out randomly, and gave them the key of names and color combinations (but no numbers). They had to find out whose test tube they had.
Diffusion of a drop of dye mixture through filter paper. At least three different colors are visible. The colors at the outer edge are the most difficult to distinguish.
I was kind enough to give them a few little demonstrations of chromatography I’d been experimenting with over the last day or so. The easiest technique is simply to place a couple drops of the sample on a filter paper (we used coffee filters “requisitioned” from the teachers lounge), and chase it with a couple drops of water to help the dye spread out. This method works, but since the sample spreads out in a circle, the inverse square law means that the separation of colors can be hard to see.
While the drop method worked well for most students, one who was a bit more analytically-minded, interested in the project, and had a particularly difficult sample, tried doing it using a filter paper column. Since I wanted to show them the proper way of conducting experiments, particularly about the importance of using standards, and I wanted to check if they were able to interpret their results correctly, I also did the full set of samples myself as columns. The standards are essential, because the green food color is actually a mixture of green and blue dyes.
Our color chromatography setup is as you see at the top of this post. We used popsicle sticks to keep the filter paper strips away from the glass surface.
Experiment with filter paper taped to the glass.
The experiments worked well, and for best results, let the it dry because the colors show up better. One focus with my students was on note-taking and recording results; after a few iterations that worked out well too. Another nice aspect of using the series of columns is that it looks a lot like the electrophoresis bands.
I did try some other variants of the chromatography: top down, bottom up and even taped down. The last version, where I taped the filter paper to the glass to create a restricted column, worked very well.
Variants of the experimental setup are shown in the three columns from left: taped down where the filter paper is taped to the glass; bottom up, where movement of the water and die is driven by capillary action; and top down, where the sample droplet is placed at the top of the column.
NYU scientists have traced the evolution of tomcod fish that’s been driven by pollution in the Hudson River. The NPR article is nice because it really breaks down how fish with the right genes preferentially survived the PCBs and dioxins in the river, and passed their genes on.
It also turns out that the fish “selected” for pollution tolerance end up being more sensitive to other things, like high water temperatures. It really puts, “survival of the fittest” in context. The fish are “fit” for polluted rivers, but not “fit” for warmer water.
Misha Angrist, who is having his entire genome published online, argues that extricating genetic diseases from the population can have unintended consequences:
“… the genome is a dynamic thing, and a balancing act. Sickle cell trait has persisted because carrying it protects one from getting malaria. Who’s to say that carrying one copy of a cystic fibrosis mutation doesn’t similarly protect us against cholera or various diarrheal illnesses? If we eliminate those mutations from the population, are we opening the door to a future of intestinal problems?
–Misha Angrist in an interview with Maud Newton, A Conversation with Misha Angrist, Publisher of His Genome
