Mendelian Inheritance

in Sunflowers

Mendel’s laws are the core ideas in biology education and the first set of concepts students learn about heredity and inheritance. However, these concepts are often taught as facts. Students are told about the Mendel’s story and ideas without being provided the experience to reasoning about inheritance patterns like scientists.

Use this model to explore Mendelian inheritance in sunflowers like a scientist. Explore how three phenotypes are inherited and test your hypotheses instantaneously. Seven cases are available for you to explore monohybrid, dihybrid and trihybrid.

Grades: 6-12, College introductory biology

NGSS Standards: MS-LS3-2

HOW TO USE


NetLogo version: 6.0.4 or higher


  1. Choose one of the seven cases.
  2. Press on “Start/reset Simulation” button to confirm.
  3. Click on “Press and choose flower(s)” button.
  4. Now use cursor to choose sunflower(s) in the simulation window.
  5. You may choose one sunflower to conduct self-pollination, or choose two flowers to conduct cross-pollination.
  6. Examine offspring sunflower frequencies in “Progeny” section.

HOW IT WORKS


Sunflowers vary in color, inflorescence, and disc color. Image from Cvejić et al. (2016)



Model Rules:

  • Three genes are involved. Each gene determines one character.

Y --> floral color; S --> inflorescence type; C --> disc color

  • Only complete dominance is involved.
  • Gametes are produced based on the parent sunflowers, following the laws of segregation and independent assortment.
  • In self-pollination, gametes randomly fused to form offsprings.
  • In cross-pollination, gametes of one parent sunflower will randomly fuse with the gametes of the other parent sunflower.
  • The number of offspring slightly vary in each generation.


Notes:

  1. This model is created based on the studies from Cvejić et al. (2016) and Divita et al. (2012), which have suggested that the genes of floral color and inflorescence type are inherited independently. In this model, it is assumed that disc color is also inherited independently in relation to the floral color and inflorescence type.
  2. Depending on the cases, a number of gametes containing three alleles, one for each of three genes, are first produced and then randomly fuse to form sunflowers. Therefore, the sunflowers you get at the beginning can be either heterozygous or homozygous. You will not be informed about the dominance and recessiveness of the presented traits. WHAT?!!! Yes, let’s face this and keep two things in mind: 1) scientists do not just get purebred individuals automatically and 2) they don’t just know which trait is dominant or recessive . They have to identify them! This model allows you to work like a scientist to figure out the dominance and recessiveness of floral color, inflorescence type and disc color in sunflowers.
  3. When you conduct test cross, the number of offspring slightly varies in each generation. Combining the random fertilization of gametes, you are unlikely to always get the ratios that perfectly match the theoretic ones. This situation mimics the authentic studies, in which scientists rarely get perfect numbers but focus on identifying data patterns.

TEACHING SUGGESTIONS

Vase with Twelve Sunflowers (Vincent van Gogh 1888)

See a detailed Teacher's Guides here.

Engage

Present the large number of variations in sunflowers using images and even some famous art work, e.g., the sunflower series from Vincent van Gogh. Use real sunflowers if possible. Let students observe the images and identify different traits in sunflowers. Prompt students to ask questions regarding the inheritance of these traits.

Explore

Let students explore the inheritance of floral color, inflorescence type, and disc color using the simulation. Focus on observing the phenotype inheritance patterns. E.g., what color do the offspring sunflower display when a yellow sunflower crosses with an orange sunflower? Have students record their predictions and simulation results on a science notebook. At the end of the class, let students share their results and discuss what causes the inheritance patterns.

Explain

Introduce terminology and Mendel's law through a short lecture or reading. Let students connect the terms , such as dominant, recessive, gene, allele, trait, etc., to the above investigation. Ask students to use Punnett square to explain their observations and data from the simulation. Teacher may reveal sunflower genotypes in the simulation and invite students to predict phenotypes and genotypes of next generation.

Extend

The simulation provides three cases of monohybrid, three cases of dihybrid, and one case of trihybrid. Teachers may use some of these cases to help students learn about Mendel's law, and use other cases to extend student learning. High school students and college students may be asked to collect numeric data from the simulation and then perform chi-square goodness of fit tests to analyze the data.

Evaluate

Students should be able to identify dominance and recessiveness of floral color, inflorescence type and disc color and provide explanations supported by the evidence from the simulation.

Students may be asked to predict offspring phenotype and ratio from the cases, e.g. case 7, and construct a written explanation.

CREDITS & REFERENCES

This module is made by Dr. Lin Xiang at the University of Kentucky. If you mention this model in a publication, we ask that you include the citations below.

Xiang, L. (2018). Mendelian inheritance in sunflowers. Department of STEM Education, University of Kentucky, Lexington, KY. https://sites.google.com/view/3d-science-ABM/genetics/mendelian-inheritance


References:

Cvejić, S., Jocić, S., & Mladenović, E. (2016). Inheritance of floral colour and type in four new inbred lines of ornamental sunflower (Helianthus annuus L.). The Journal of Horticultural Science and Biotechnology, 91(1), 30-35.

Divita, M. E., Salaberry, M. T., Echeverría, M. M., & Rodríguez, R. H. (2012, February). Genetic and environmental effects of some traits of ornamental value in sunflower (Helianthus annuus L.). In Proc. 18th Int. Sunflower Conf., Mar del Plata (pp. 566-574).