For most of the year, deciduous trees are green because of chlorophyll in the chloroplasts.  This pigment helps harness energy from the sun to fuel photosynthesis, or food production.  In the fall, days become shorter and sunlight more sparse, so plants begin to prepare for the winter – a period during which they rely on stored nutrients.   Nutrients are stored and superfluous leaves are shed , but before that, the chlorophyll begins to disappear, revealing other pigments such as yellow and orange that weren’t visible before.  Sometimes during this process, new pigments (such as reds) are produced as well.

This is controlled by up to 35 genes that can turn on and off in response to the reduction of sunlight hours.  It is a great example of the interaction between an organism’s DNA and its environment, a phenomenon many people are unaware of.  The traits and characteristics of all living things are the result of a combination of its genetic makeup and its physical and chemical surroundings.  To learn more about this type of interaction, go to chapter 35, “DNA responds to signals from outside the cell.”

Interestingly enough, the Spruce, a very common Christmas tree species, has seven times more DNA than a human. How is that, you say?  They are but simple trees, and we are complex animals with skills and intellect beyond compare! Well, you may not say that, but my students do! I shared that little gem with my class today, and they were shocked.

It turns out that all conifers like the Spruce, have 12 chromosomes (humans have 46), but they are really big. Scientists aren’t sure why this is so, but some speculate that this large amount of DNA may be how they have been such a successful plant, surviving for millions of years. There are several plant species that have way more DNA than we do, which brings to light the questions: Does more DNA make an organism more complex? Could a plant be more complex than a human? I suppose that depends on who you ask.

What I do know is that I love my Christmas tree, and all 12 of its giant chromosomes!

To read more about the Spruce geneome project in Sweden, go to: http://www.innovations-report.com/html/reports/agricultural_sciences/christmas_tree_times_dna_time_map_145376.html