Instruction on how to extract DNA from anything, (I’m going to use this as a lab and perhaps to make pea soup too) and specifically, from people (inside of your cheek).
Drosophila (fruit fly) head. Fruit flies are used extensively in biological and genetic experiments (image from Wikipedia).
Hannah Waters at Culturing Science has nice post on an experiment designed to find out how fast a population of flies could adapt to dryer conditions. Apparently, the flies could not adapt.
We tend to take it for granted that life is robust, and will adapt: “Life will find a way”. This is true to an extent, but obviously not always:
Natural selection itself is based on three assumptions in a population. The first is that there will be variation in traits, such as multiple colors of eyes or hair. The second is that these traits be heritable through the generations, that children will inherit the traits of their parents. The third is that these variable traits have differential fitness, or that some versions of a trait might help you survive better than another. Thus certain trait variants will help its carrier organism survive better, passing that trait to its offspring which will in turn bear this trait. – Waters, 2011: When adaptation doesn’t happen.
Punnet square for a gender conferred recessive trait.
Two X chromosomes (XX) makes women female. Men have an X and a Y, the latter of which is responsible for all the things that make them male. What we teach is that one of the X’s in the women’s XX’s dominates the other so that women’s physical characteristics (phenotype) is only determined by the dominant X. Recent research shows that’s not necessarily the case.
“Our study shows that the inactive X in women is not as silent as we thought,” said Laura Carrel, Ph.D., assistant professor of biochemistry and molecular biology, Penn State College of Medicine, Penn State Milton S. Hershey Medical Center. “The effects of these genes from the inactive X chromosome could explain some of the differences between men and women that aren’t attributable to sex hormones.” – From Penn State University, edited by Science Daily.
It’s a fascinating finding, but I don’t think I’ll go into it with the students except, in the very unlikely event, that a direct question comes up. At this point, simpler is better.
Wired has a brief but excellent article on the voyage of the Beagle.
Its goal was to survey the South American coastline. The captain invited along a young man named Charles Darwin, whose father thought the voyage would just be another excuse for him to slack off. The trip ended up taking five years.
This article would be a wonderful addition to our work on exploration of the Americas next time it comes around; however, it’ll also be a neat little footnote because we’ll be delving into evolution next cycle.
Wikipedia’s entry on the ship produced this wonderful cross-section. I particularly like the sketches of people and casks showing the use of of different cabins and spaces.
It starts with evidence that the mitochondria in our cells were once separate organisms and goes on to explain things like how the change from quadrupedal to bipedal, upright walking resulted in our S-shaped spine (and frequent backaches) and our unsupported intestines. It’s quite the interesting read.
Figure 1. Undigested fiber from rabbit fecal pellets.
One of my favorite things is when my students teach me something I didn’t know. One of those things is that rabbits eat their own poop.
Well not exactly. According to Dana Krempels, from the University of Miami, rabbit fecal pellets (poop) are different from the other type of droppings that lagomorphs actually eat, which are called cecotropes (Kempels, 2010; Rabbits: The Mystery of Poop). Cecotropes apparently have lots of helpful bacteria and nutrients. Rabbits that don’t get to eat them tend to suffer from malnutrition.
Figure 2. Rabbit fecal pellets, with one mostly dissected, in a standard petri dish.
Independent Research Project
For her Independent Research Project (IRP) this term, one of my students researched rabbits, and, as was required, tried to find them on our nature trail. She found indirect evidence. Small fecal pellets in the grassy area next to the trail’s exit, just where her research said they might be (which was quite nice). The pellets were brought inside, dissected, and examined under the microscope (see Figures 1 and 2).
The magnified image showed what appeared to be a partially masticated (chewed) piece of fiber, probably grass. This is where I was informed about the double eating called cecotrophy. My student hypothesized that this sample might be something that had not been fully digested and the rabbit would come back and eat it another time.
The Scientific Process
I really like the scientific process that went into this project, even though I’m not sure I agree with the final hypothesis. The project started with background research that yielded a plan for field observation. The field observation resulted in samples being collected and returned to the lab for analysis. The analysis produced some interesting, enigmatic results, which lead to a proposed hypothesis that integrated the observations based on the original background research.
The only things I would like to add to this type of IRP is to have students include a detailed scientific sketch, much like the sketches of the early botanists and naturalists. I really like how these drawings integrate acute observation and artistic interpretation.
We’ve seen that autotrophs get their energy from sunlight or chemical reactions, while heterotrophs get their energy from eating other organisms. We’ve also seen that some protists, called mixotrophs, can do both.
We have not yet discussed reptiles, which are heterotrophs (as are all members of the Domain Animalia), but use the sun to regulate their internal temperature (they’re ectotherms).
The researchers used the pigment to make their own solar cell, but it proved to be quite inefficient, only converting 0.335% of the incoming light to electricity. However, the microscopic ridges on the hornet, and the layering of the insect’s cuticle, suggest that the hornet itself is more efficient.
I’m not quite sure how the hornets would use the electricity if that’s what they’re doing, but they are more active in sunlight than in the dark, so some type of “solar harvesting” is probably going on.
Amargosa Toad (Bufo nelsoni). Photo from US Fish and Wildlife (M. Burroughs).
NPR had facinating story recently about unlikely groups working together. It’s about a town in Nevada that banded together to save a toad from going extinct. The groups working together include environmentalists and the Saving Toads thru Off-Road Racing, Mining and Ranching in Oasis Valley (aka STORM-OV).
