Biology, The Science of Life

Mendelian Genetics

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Overview: Today’s lesson will consist of the teacher lecturing for approximately 40 minutes of the duration of the class. This lesson presents some mathematical concepts, therefore the teacher is required to follow the Power Point presentation very closely and make sure every student is comfortable with the material every step of the way since the material builds on the information presented in the previous slide. Students will also be presented with an image (available below) and will be asked to think critically about it as an introduction to the next class. Finally, an assignment will be handed out at the end of class.

Materials: The teacher will need the class computer, screen and projector to present the Power Point presentation for approximately 40 minutes of the class. A white board will also be a necessity to further emphasize the examples presented on the slides and to answer any questions a student may present. Students will need pencil and paper to do the problems at the same time as the instructor.

Assessment: An assignment with various problems on Punnett squares and Mendelian crosses is assigned because since this topic has a mathematical aspect, problems and practice are a good review tool. The assignment will be worth 10% of the students’ final grade.


  • Introduction to Mendel and his experiment (7 minutes)
  • Go through the Power Point and problems (35 minutes)
  • Science in Society: Show picture and induce a discussion (7 minutes)

Provide a brief introduction of Mendel and his experiments.

Mendel grew up on his parent’s farm in a region of Austria which is now Czech Republic. Around 1857, Mendel began breeding garden peas to study the concept of heredity. One reason Mendel chose peas to work with is because they are available in many varieties. For example, one variety has purple flowers and the other white. A heritable feature that varies among individuals, such as flower color, is character. Each variant for character, such as purple or white color for flowers, is termed trait.
A plant is said to be true-breeding, if for example, the seeds of a plant with purple flowers produced by self-pollination in successive generations all give rise to purple flowers.
In a typical breeding experiment, Mendel cross-pollinated two contrasting, true-breeding pea varieties – for example, purple-flowered plants and white-flowered plants. This mating, or crossing of two true-breeding parents are referred to as the P generation, and their hybrid offspring are the F1 generation. Allowing these F1 hybrids to self-pollinate produces an F2 generation.

The alternative version of a gene is called an allele. An organism inherits two alleles, one from each parent. Therefore, if the two alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organisms appearance, or phenotype.
An organism that has a pair of identical alleles for a character is said to be homozygous for the gene controlling the character. An organism that has two different alleles for a gene is said to be heterozygous.

Begin Power Point presentation. Remember to go through every slide slowly and to make sure every student understands.

Science In Society

Once the Power Point presentation is done, present this image (below) on the screen and induce a class discussion regarding the picture.

Point out the fact that the spiral staircase is symbolic to the man in the wheel chair’s DNA helix. He is looking up at  his DNA, wondering why it is he cannot use his legs to go up those stairs. (7 minutes)
Questions may include:
  1. Do you believe our fate is pre-determined by our DNA?
  2. Is Mendel’s model of predicting the probability of our genes components a valid tool to predetermine our biology?
  3. Do you think Mendel’s pea plants predictability experiment can justify the genocide of WWII?

Hand out the assignment and if there is time remaining at the end of class, allow students to being working on it in groups.
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