The game can help...
As the students play the game, they will observe the basic guidelines of Mendelian genetics. They will see that each offspring robot receives half its alleles from each parent robot put into the recycler. Likewise, the students will observe that some alleles are dominant—when they are paired with other, recessive alleles, the dominant trait is exhibited by the offspring robot. With this knowledge, they can “breed” specific robots for specific traits to win battles.
Punnett squares and dominance
A teacher has introduced Punnett squares to her students. She points out that offspring get one allele from each parent, and that dominant alleles are represented by upper-case letters and recessive alleles are represented by lower-case letters. She describes the recycler in the game as an animated Punnett square, except that the alleles are pictures instead of letters. She projects the Robopedia from her laptop, pointing out that each robot has two alleles, one from each parent. These alleles determine whether a particular robot is a Sand, Rock, Laser, Water, or Fire robot. “The dominant allele determines the trait.” She points to the Rock robot and asks the students which alleles they see. They respond, “Rock,” and “Sand.” She then asks them which allele is expressed and which is not. The students reply, “Rock is expressed,” and “Sand is covered up.” She then explains that this is similar to what they see with Punnett squares.
Slides 3–10 address many of the issues around Mendelian genetics. Slides 3–8 explain the vocabulary necessary to talk about genetics, including gene, allele, dominant, recessive, genotype, phenotype, homozygous, and heterozygous. Slide 9 uses eye color as an example to show how phenotype results from the different possible genotypes for two alleles displaying a simple dominant/recessive mode of inheritance. Slide 10 shows all the possible outcomes for the different possible parental genotypes.
What the Textbooks Say
Almost every textbook devotes a great deal of space to Gregor Mendel’s experiments with breeding peas in order to explain five main ideas:
- Selective breeding can produce a strain that breeds true for a particular trait;
- Cross-breeding two different pure-breeding strains expresses the dominant traits;
- Breeding the offspring of a breeding of two different pure-breeding strains will express both the dominant and recessive traits;
- The pattern in 3, above, is due to the fact that every plant receives two factors for each trait—one factor from each parent.
- This explains how traits that are not expressed in one generation can reappear in the next.
Students often are unable to correctly describe the nature of simple dominant and recessive patterns of inheritance. They may believe that all traits are inherited from only one parent, or that certain characteristics always come from one parent and other traits always come from the other parent.