Dr. Christine Jurasinski
LabLearner Staff Scientist

Mutation, allele, gene.  What do you think of when you hear these words?  Perhaps DNA comes to mind or disease or the workings of a cell.  But what about evolution?  For many, evolution brings to mind words like Darwin, finches, beaks, and fossils rather than mutations, alleles and genes.

But what about LabLearner students?  While they may begin their exploration of evolution, adaptation, mutations and natural selection by focusing on each of these topics in discrete CELLs such as Ecosystems and Adaptation,  Inheritance and Adaptation, and Genes and Proteins, they have the opportunity to combine all of this knowledge into a more complex and more scientifically “real” concept in the 7^th grade CELL Adaptation: a CELL that sets them up for understanding some of the latest research into the molecular mechanisms for how species adapt and evolve.

This newest research comes out of the lab of Dr. Erica Rosenblum of the University of Idaho.  She and her colleagues have uncovered some intriguing information about the genetic process of evolution.  Their research is centered around three species of lizards. Each of these three species exist with dark skin in many areas around the world but have evolved a white skinned variation in the White Sands of New Mexico.  And what strikes the researchers as amazing is that in two of the species, it was accomplished by DIFFERENT MUTATIONS in the SAME GENE.  Even more interesting is that one mutation is DOMINANT while the other is RECESSIVE.

As fifth grade LabLearner students learn, many organisms have two copies of each gene.  One copy on one chromosome.  The other on the other chromosome.  The two copies of the gene are called alleles.  In one of the simplest examples of inheritance of traits, one allele is dominant the other is recessive.  Organisms with two dominant alleles will show the dominant version of a trait such as brown fur.  Organisms with one dominant and one recessive allele will also have the dominant brown fur trait.  However, organisms with two recessive alleles will have the recessive trait of white fur.

What Dr. Rosenblum discovered was that in one species of lizard, the white skin was the result of a dominant allele but in the other species of lizard, the white skin was the result of a recessive allele.  In both cases, the lizards evolved from having brown skin, but it was through different methods of inheritance.

How did this happen?  The answer involves selection pressure and mutations.  About 5000 to 7000 years ago, evaporating lakes in that area of New Mexico left behind huge deposits of gypsum which eroded away leaving an entirely white area of desert in what had once been a brown area.  Lizards which had been living there were brown skinned, which served as excellent camouflage from aerial predators.  However, as the terrain began to change, brown skin against and increasingly white background no longer served to camouflage the lizards, making them easy prey.

What scientists believe happened is that a mutation, a change in the DNA in the gene that controls the color of pigment in the lizards’ skin occurred.  This mutation may have occurred before but would not have likely been retained in the lizard population because white skinned lizards in a brown desert would have been an easy target for predators.  However, a mutation that occurred when the sands were white would have produced white skinned lizards that blended in with their surroundings.  These lizards would have been more likely than the brown skinned lizards to survive to produce offspring.  These offspring would have the mutated gene for producing white skin.  Thus, more and more lizards with allele for white skin would be born because the white sands now “selected for” this allele.

In one species of lizard, the mutation was dominant meaning the trait produced by the gene required only one copy of the gene in order for the skin to be white. The gene on only one chromosome had to be present. In the other species of the lizard, the mutation was recessive.  In other words, in order for the skin to be white, both copies of the mutated gene (one on each chromosome) had to be present.

For 7^th grade LabLearner students, this real life example with the lizards epitomizes the concepts they have learned in the Adaptation and Genes and Proteins CELLs.  Evolution and natural selection occur because of changes in DNA.  Changes in DNA can result in differences in proteins and thus traits produced in an organism.  These types of changes can be seen by looking at the frequency of alleles for a trait.  If one trait is selected over another than the allele which produces that trait will appear more frequently in the population.  This is what Dr. Rosenblum and her colleagues would expect to see when comparing the alleles for skin color in lizards in the White Sands area to those same species of lizards in other areas of the world with a brown habitat.

For LabLearner students, the next question would be:

Which species of lizard would you expect to evolve faster, the ones with the dominant or recessive allele?

Based on what they know about modes of inheritance, those 7^th grades and even 5^th graders should predict—lizards with the dominant allele.  It’s what Dr. Rosenblum predicts and what she and her colleagues will continue to explore.

From her research and those of so many others we see that evolution and our study of it continues. What makes it different from Darwin’s time is that we now have the molecular tools to better understand how and why.

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