Genetics

The first slide on this unit's PowerPoint shows photos of faces of some people who may or may not be related.  (In fact, the two sets of adults pictured are twins).  Additionally, there is a photograph showing hydrangeas of different colors.   I lead the class in a discussion about genetically inherited traits (both observable and not), as well as environmental effects on those traits.  We talk about "nature vs nurture".  ​

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​Earlier in student's academic careers, they have learned about Mendel.  I discuss Mendel in more detail.  I position my discussion historically.  I also discuss the Nature of Science (NOS)  in this unit because Mendel's story offers good examples of how science is unlike other academic subjects (e.g.History, English) or non-academic subjects (e.g. how to change the toner on a Canon Printer, run a meeting according to Parliamentary Rules, or properly perform a kick serve in tennis).

​Science relies on empirical evidence and logical thinking. In science, knowledge is tentative and modified as new information is learned. It is not dogmatic. Types of knowledge are identified as either hypotheses, theories or laws.  Science has creative elements, as well.  Science is impacted by history, culture, & society. It is important, also, to understand that science can’t answer all questions....only those that are testable.

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​You can find a video below with several guys dressed as monks singing about Mendel.  The lyrics give some accurate information about Mendel to a "sick" beat.  ; o )

I tell students what genes and alleles are and give them some specifics about how Mendel performed his experiments.  Mendel showed that genetic outcomes are based on probability.  He used the terms dominance and recessiveness.  It is important that students understand the terms heterozygous/hybrid and homozygous/pure.  We practice Punnet Squares and (FREE) pedigree charts. ​

​I next review Mendel's Principals of Segregation and Independent Assortment. In my talk about these principals I tell students that Mendel's work with pea plants did not reveal that, in fact, certain genes tend to be inherited together and are "linked".  I discuss the mapping of the fruit fly genome and give a couple of examples of gene linkage.

Although examples such as "hitch-hiker's thumb" are sometimes given as Mendelian Traits, in fact, characteristics such as these appear as a continuum in humans; they are not limited to two alleles.  Here is a worksheet where students learn that Mendelian traits are rare in humans.  ​

​I further explain that there are a number of other exceptions to  Mendel's principles.  I offer the examples of co-dominance and incomplete dominance.  Here is an assignment about co-dominance in terms of human blood typing.  

​Students next complete a (FREE!) LAB:  Inheritance is Based on Probability, where they roll dice to determine traits about an imaginary offspring.

​Earlier in the school year, during the reproduction unit, students learned about crossing-over during meiosis.  I tell students:  if meiosis progresses normally, chromosomes undergo disjunction.   If meiosis does not progress normally, chromosomes may undergo nondisjunction.   Mutations can occur when chromosomes don't separate or separate incorrectly.  I also briefly mention gene mutations, which I return to later in the unit.

Since I have previously mentioned how some environmental factors (e.g.:  X-rays, formaldehyde) can cause mutations, I renew our discussion about how the environment effects gene expression.  ​

​Continuing on the theme of mutations, I mention a couple of genetic disorders and some screening methods currently used.  Students next complete a KARYOTYPING LAB where they get some experience using one of the screening methods that I discussed.  ​

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Next we talk about the arrangement of the actual DNA molecule. Students complete a (FREE!) DNA MODEL LAB.  They learn about how and where DNA replication occurs.  Students learn about how the molecule unzips and that the original strands are used as templates for making new strands.  I follow with an activity which focuses on the nitrogenous bases and the laws of base pairing.  ​

​During the discussion of transcription and translation, students learn about RNA and practice using both the amino acid chart and wheel. I also revisit the topic of gene mutations.  This is an excellent time to show the video DNA:  The Secret of Life, which can be found on YouTube.  Here is a video worksheet that goes with the movie.  ​

Students then complete a PROTEIN SYNTHESIS LAB where they practice DNA replication, transcription, and translation.  They discover and identify a number of genetic mutations in this lab.

​Next, we move to advanced DNA manipulation techniques.  I describe the following techniques to students:  
​DNA extraction, the use of restriction enzymes and recombinant DNA, gel electrophoresis, and PCR (polymerase chain reaction).  A video below shows a demonstration of gel electrophoresis.  Students complete a DNA FINGERPRINTING LAB, in addition to a number of other activities designed to enhance students' understandings of biotechnology.

Another technique I focus on specifically is cloning.  I show a video (video worksheet found here) and have students complete a writing assignment on the process.  ​

Finally, I discuss the use of viruses in biotechnology.  I address controversial topics such as transgenic or genetically modified organisms. We finish up the unit discussing the benefits and drawbacks of GMOs.

The Presentation and Student Notes files are available here. ​