The vignettes and materials presented here will help you understand how the Possible Worlds resources can be integrated with your existing approach to these topics. They are intended to help you make connections between the core mechanics of the games and the phenomena related to common scientific misconceptions.
The desire to get the right robot to win the game focuses the player's attention on the random nature of robot heredity. The recycler in RoboRiot helps students to visualize and experiment with the notion of randomness. When they put a pair of robots in the recycler, they can see that there is a random selection of alleles from both sides. Randomness is in play, because you cannot be sure which allele will be contributed by each robot. Each try in the recycler produces an unpredictable outcome or pairing of alleles, and the outcome of each try does not affect future attempts.
The relationship between random inheritance and robust species populations
A teacher introduces the concept that, because traits are randomly inherited, genetic diversity is important for the stability of species populations. He uses the RoboRiot game to ground the discussion, noting that, because all of the recycler outcomes are random and cannot be chosen by the player, successful gameplay requires a player to have a variety of alleles, making more random outcomes possible. He refers to an experience that many students had during gameplay—they were better prepared to confront whatever type of robot came their way if they established a large and diverse robot team. The teacher explains, “When you selected a robot for an encounter, the ability to choose from a variety of robots helped you win. In the real world, the more alleles there are, the better the chances of survival. Different alleles must be present to be candidates for selection.”
While most textbooks address the concept of meiosis, explaining that during this process pairs of chromosomes separate and that alleles for each trait also separate into different sex cells, little if any time is spent helping students understand that this is a random process. This idea of chance is sometimes addressed using a coin toss activity, but how chance relates to meiosis is not given much attention. The role of chance in the combining of sex cells is further complicated when students are introduced to Punnett Squares and learn that you can mathematically predict the traits of offspring, if you know the genetic makeup of the parents and the traits follow a simple dominant-recessive pattern of expression.
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.
Almost every textbook devotes a great deal of space to Gregor Mendel’s experiments with breeding peas in order to explain five main ideas:
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.
As students learn about the various possible combinations of robot alleles and how they combine, they will observe, e.g., that when fire and ice alleles are paired, neither is dominant. Instead, the resulting water bot is a combination of the two traits. When this pattern occurs in nature, such as with blood groups, it is called incomplete dominance, a complex pattern of genetic inheritance.
A teacher explains to the class that there are many traits that are inherited in ways more complex than a simple dominant/recessive relationship. She explains that one such example is human blood types, where there are more than two possible alleles —A, B, and O—and, while some combinations display a simple dominant/recessive relationship (AO and BO display only the dominant allele, A and B, respectively), in one pair, AB, both alleles are expressed: This is called incomplete dominance. The teacher puts up the Robopedia entries and asks the students to identify which alleles have a simple relationship and which have a complex relationship.
Slides 11 and 12 describe a case where the simple dominant/recessive relationship does not apply. The slides describe the case of co-dominance using human blood types as an example. There are three alleles possible for human blood types: A, B, and O. Alleles A and B are dominant over O, but are co-dominant, meaning that when an individual has both the A and B allele, BOTH are expressed at the same time.
A section of text usually explains the exceptions to the Mendelian model.
A common misconception is that single genes are the cause of most traits and inherited diseases.
During gameplay, students will see that each robot type is defined by one pair of alleles, and that each bot gets one allele from each parental bot put into the recycler. This process mirrors inheritance through sex cells. Each human has two pairs of each type of chromosome, and gets half of each pair from the parents. The half-set of chromosomes is passed from each parent to the offspring via sex cells—sperm and ova. When the sex cells combine, a new individual is produced with a full set of chromosomes.
A teacher introduces the concept that organisms, such as humans, contain two pairs of each type of chromosome (the genetic materials that hold alleles), and produce genetically unique offspring by each parent providing half their genetic material. It is randomly determined which half is passed on during the production of sex cells (sperm and ova); the sex cells from the parents combine to produce offspring with a full set of genes. The teacher then asks which part of the game reflects this process. The students reply by describing the process of using the recycler, and its role in generating offspring robots.
Slides 2, 3, and 4 relate to the process of reproduction. They highlight that both parents have two homologous pairs of each allele, and pass only one half of each pair to the offspring. While the slideshow does not mention sex cells, they are cells that contain half the genetic material of each parent, and are combined to produce the offspring. When sex cells are made, the genetic material is randomly divided so that each sex cell has one half of each homologous pair of each allele.
Some textbooks cover egg and sperm cells in the genetics chapter. They generally explain that dominant and recessive traits are carried by chromosomes, that chromosomes are made up of long strands of DNA, and that a gene is one section of the DNA strand. Unlike other cells, which contain two sets of chromosomes, sex cells each contain only one set. When an egg cell and a sperm cell fuse, they create a pair of chromosomes for their offspring; the offspring’s chromosomes are different from those of either parent. A single gene on a single chromosome in a sex cell is called an allele. Two alleles—one from each parent—form their offspring’s genes. Students frequently do not understand the relationships among DNA, chromosomes, and genes.