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Title: Model Mendelian genetics and the inheritance of traits
Principle(s) Investigated: Mendelian genetics and inheritance of traits.
7.2.b - Students know sexual reproduction produces offspring that inherit half their genes from each parent.
7.2.d - Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive.
7.7.c - Communicate the logical connection among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence.
7.7.d - Construct scale models, maps, and appropriately labeled diagrams to communicate scientific knowledge 9e.g., motion of Earth's plates and cell structure).
Materials:
Each group of 4 students receives:
- 2 coins
- colored label-dots (red & blue)
- gumdrops (red & orange)
- marshmallows (large)
- pipe cleaners - 5cm (red & green)
- map pins
- pushpins (green & blue)
- pipe cleaners - 8cm (one color)
- toothpicks
- scissors
Procedure:
- Teacher will describe the fictional story of a team of scientists who discover a new species. These organisms resemble insects in many ways, but due to other strange and "alien" traits, scientists have dubbed them "Space Bugs". After observations, these Space Bugs appear to inherit traits according the Mendelian genetics - the principles discovered by Gregor Mendel.
- Students get into groups of 4 and are given the chart of Space Bug Traits and Alleles.
- Students collect trays containing materials needed.
- Students within groups work in pairs to construct the female and male Space Bugs based on the chart. Toothpicks can be used to connect body segments and attach feet. Groups complete SHEET 1 of data table by entering phenotypes for given genotypes.
- After building the parents, students will label two coins using red stickers for mom's alleles and blue stickers for dad's alleles. Students will flip both coins to determine the first trait the offspring will inherit from its parents. Students will adhere new set of stickers for each trait, and take turns flipping the coins and entering the genotype and phenotype of their offspring in the Data Table (sheet 2).
- Based on the inherited alleles, students will work together in building their Space Bug offspring.
- Whole class: determine the ratios for each trait.
- Whole class: complete Punnett squares and compare hypothetical results with actual results.
- Compare offspring models. Do any offspring look identical?
Student prior knowledge:
- Students must have the basic understanding that organisms inherit half of their genes from each parent due to meiosis.
- Some genes may be dominant while others are recessive, and that dominant genes mask recessive ones.
- Dominant alleles are represented by UPPER case letters, and recessive alleles are represented by lower case letters.
Explanation:
This lesson should follow an initial introduction to Mendelian genetics. Begin the lesson with a review of key vocabulary and concepts. Students should recall that parents give half of their genes to their offspring through meiosis. Since each parent gives a set of their genes to their offspring, the offspring will have two different versions of the same gene (homologous pairs). The different versions of a gene are called alleles. For this lesson, dominant alleles will have "complete dominance" rather than incomplete or co-dominant traits. Complete dominance occurs when a genotype with a dominant allele (uppercase letter) would complete mask the recessive allele. The labeling and flipping of the coins reinforces the complete randomness of inherited traits, and that our characteristics are based completely on chance, just like a coin toss.
Questions & Answers:
Q: Could an offspring have traits neither of its parents has?
A: Yes. If both parents have a dominant and a recessive allele of a trait (i.e. Rr = red), it is possible for the offspring to inherit the recessive allele of both parents (rr) and exhibit the recessive trait (green).
Q: If one of the parents was homozygous dominant, as in the case of its nose color (BB) and the other was heterozygous (Bb), could the offspring have traits neither of its parents has?
A: No. In order to have recessive traits, the offspring would have needed to inherit recessive alleles from both parents.
Q: How is the inheritance of traits in these Space Bugs like the inheritance of traits in humans, and how are they different?
A: In both the Space Bugs and humans, traits are influenced by the copies of the parents' alleles. However, human trait inheritance is more complicated in that many of our traits are influenced by many multiple genes as well as the environment.
Applications to Everyday Life:
- Parents who are carriers of a genetically inherited disease may seek genetic counseling when deciding to have children. Punnett squares can be used as a predicting tool to determine the probability of a healthy/unhealthy child.
- Dog breeders may utilize the Mendelian principles to produce puppies with desirable traits. This, however, has lead to skeletal problems in some breeds of domestic dogs.
- In agriculture, farmers have long been selecting plants with desirable traits in order for productive next generation crops. Unfortunately, sometimes these selected breeding experiments can lead to disease in crops.
Photographs:
Videos:
A Beginner's Guide to Punnett Squares-YouTube: http://www.youtube.com/watch?v=Y1PCwxUDTl8&feature=related
Genetics 101 Part 1-What are Genes-You Tube: http://www.youtube.com/watch?v=eOvMNOMRRm8&feature=youtu.be
Genetics 101 Part 3-Where do your genes come from?-You Tube: http://www.youtube.com/watch?v=-Yg89GY61DE&feature=relmfu
Genetics 101 Part 4-What are Phenotypes-You Tube: http://www.youtube.com/watch?v=kLpr6t4-eLI&feature=relmfu
Credits: HOLT California - Life Science
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