This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.

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The purpose of this assessment probe is to elicit students’ ideas about heredity. The probe is designed to reveal how students think organisms inherit observable traits.

Friendly talk

Inherited traits, genes, sexual reproduction

The best response is Alexa’s: The baby mice got half their inherited information from their father and half from their mother. The first step in the production of offspring from the two mice is fertilization of the female’s egg by the male’s sperm. Egg and sperm each contain half the number of mouse chromosomes. Genes are found on chromosomes. A gene is a segment of DNA on a chromosome that carries instructions for a particular trait, such as fur color. During fertilization, matched pairs of chromosomes (half from the mother and half from the father) come together, and a single cell results (which will divide and eventually become the baby mouse). The baby mouse contains a full set of chromosomes—with half the genes on their chromosomes coming from the mother and half from the father. The combination that results determines the offspring’s traits.

One way in which genes are expressed was described by Gregor Mendel, who believed that traits could be either dominant or recessive. When two genes for the same trait are paired and one of the genes is dominant, the dominant gene will be expressed. In applying Mendelian genetics to the example of the mouse fur color (a simplified way of looking at coat color), black fur color would be dominant. Even if the offspring had only one gene for black fur, the trait that would be expressed is black fur. White fur would be a recessive trait that is expressed when a dominant gene is not present. The white offspring would have two genes for white fur color. Mendelian genetics is a simplified first step in understanding how genes are expressed, but understanding genetics is much more complex, and the expression of a trait such as fur color in mice involves multiple genes. The key idea in this probe is that an organism’s inherited traits are determined by the pairing of genes from the mother and father, with each parent contributing 50% of the genes. The combination of genes determines which traits are expressed. It is not the result of one sex having more or stronger traits (or genes) as described in Jerome’s and June’s responses.

Black and white mice have the same number of genes (contrary to Seif’s response); they are just expressed differently. Coat color in mice is not determined by sex, as described in Fiona’s response. For example, some of the white mice could be male if they received a recessive gene from both the mother and father.

Lydia’s response is a teleological argument that implies that some intentional force of nature directs the traits that offspring will exhibit, rather than traits being the result of gene expression. However, the expression of some traits can be affected by the environment. Billy’s response is similar to historical beliefs. Before Mendel, many people thought traits were passed on through the blood.

Elementary Students

In the primary grades, students are beginning to learn about inherited characteristics. They explore traits at the organism level. They develop a theory of “kinship” by observing that offspring are similar to their parents yet do not always look exactly like their parents or each other. In the later elementary grades, they begin to develop an understanding that traits are passed on from parents to offspring and that offspring can look or function differently because they have different inherited information. They can discuss how a mixedbreed puppy looks different from its parents yet has some similar characteristics of each parent. This phenomenon should be explored with a variety of organisms. However, it is too early to introduce the genetic mechanism of inheritance. By eliminating some of the distracters, this probe can be used to examine students’ early ideas about how traits are passed on to offspring before they encounter concepts such as genes, chromosomes, DNA, and proteins.

Middle School Students

In middle school, students learn core ideas about the mechanism of inheritance, combining ideas about reproduction, cell division, and basic genetics. The focus at this level is on cellular mechanisms. They develop an understanding of the role of chromosomes, genes, alleles, and proteins in passing on characteristics from one generation to the next, including the idea that genes control proteins, which can affect how a trait is expressed. At this grade level, it is important that students understand that half of their genes come from their mother and half from their father and that this random combination results in the inherited traits they may exhibit. Students should recognize the role of chance in determining which chromosomal pairs come together during fertilization and that probability can help predict the outcome of some inherited characteristics. Students may start with basic Mendelian genetics; however, it is important for them to know that not all traits are the result of the pairing of a single gene type. A more detailed mechanism of genetics can wait until high school.

High School Students

In high school, the link between genetic information and expression of traits is further developed and deepened. Students learn more complex details of the mechanism of inheritance and how various gene combinations code for proteins and that the structure and function of proteins results in the expression of traits. They should be able to explain why some traits are expressed and some are not. They can now delve into genetics at a molecular level. However, they are not expected to know the specific steps in transcription and translation of genes to proteins.

This probe can be used with students in grades 5–12. If students have a conceptual understanding of genes, consider substituting the words traits and inherited information with the word genes.

• When asked to describe how physical traits are passed from parents to offspring, elementary, middle, and high school students all exhibited misconceptions, including the idea that traits are inherited from only one of the parents and that certain traits come from only the mother or only the father (AAAS 2009).
• Students often do not differentiate between genes and traits and may use the words synonymously (Lewis and Kattmann 2004).
• Many secondary students are unfamiliar with the role of proteins in expressing genetic traits (Marbach-Ad and Stavy 2000).
• Research has shown that students often initially conceive of genes as passive particles that are associated with traits rather than information-carrying entities (Venville and Treagust 1998).
• Use of the word dominant in regard to dominant and recessive traits may contribute to several misconceptions. For example, students may think that dominant traits are “stronger” and “overpower” the recessive trait, that dominant traits are more likely to be inherited, that dominant traits are more prevalent in the population, that dominant traits are “better,” and that male or masculine traits are dominant (Donovan 1997).
• Several studies have found that even before students receive formal instruction in genetics, they know the words gene and, less frequently, chromosome. Students may know these words, but they have little understanding of the nature or function of genes or chromosomes (Driver et al. 1994).
• Engel Clough and Wood-Robinson (1985) found that some students had a tendency to favor the mother as the primary contributor of inherited traits and held a belief that daughters inherit from mothers and sons inherit from fathers. In some cases, this belief follows students right into adulthood, where it persists.
• In a study by Hackling and Treagust (1982), 94% of 15-year-old students understood the concept that one’s characteristics come from parents, 50% understood that reproduction and inheritance occur together, and 44% understood that one gets a mixture of features from both parents.
• In a study of ideas about the mechanism of inheritance among children ages 7–13, Kargbo, Hobbs, and Erickson (1980) found that half the children gave a naturalistic explanation, such as nature makes offspring look like their parents. Some thought traits were decided by the brain or blood. Only a few older children in the sample mentioned any genetic principle. In analyzing the students’ responses, the researchers found that they were not giving flippant, unthought-through answers but rather were drawing on their own conceptual frameworks to make sense of inherited phenomena.
• In an older study by Deadman and Kelly (1978) that sampled 52 students ages 11–14, researchers found that boys had a prevalent conception that characteristics from male parents were stronger in the way they were expressed.

Fetters, M. K., and M. Templin. 2002. Building traits. The Science Teacher 69 (4): 56–60.

Keeley, P. 2018. Uncovering student ideas about inherited traits. Science and Children 55 (6): 20–21.

McElroy-Brown, K., and F. Reichmann. 2019. Genetics with dragons: Using an online learning environment to help students achieve a multilevel understanding of genetics. Psychology 42 (8): 62–69.

NGSS Archived Webinar: NGSS Core Ideas—Heredity, Inheritance, and Variation, www.youtube. com/watch?v=JTTD6oZnQFc&index=4&list= PL2pHc_BEFW2JjWYua2_z3ccHEd6x5jIBK.

Shea, N. A., and R. G. Duncan. 2017. Core idea LS3: Heredity: inheritance and variation of traits. In Disciplinary core ideas: Reshaping teaching and learning, ed. R. G. Duncan, J. Krajcik, and A. E. Rivet, 145–164. Arlington, VA: NSTA Press.

Todd, A., and L. Kenyon. 2016. How do Siamese cats get their color? The Science Teacher 83 (1): 29–36.

• A driving question for middle and high school is, “How are observable traits passed on from parent to offspring?”
• Starting in elementary grades, students should have observational experiences to compare how offspring of familiar animals resemble each other and their parents, describing and drawing examples of similarities and differences.
• Several studies have suggested introducing explanations of heredity to elementary students using, initially, a very simplified idea of genetic material to serve as a “conceptual placeholder.” This can help children “hold in place” a rudimentary scientific explanation upon which more detailed explanations of inherited traits and the mechanism of inheritance can be built later (Ergazaki et al. 2015; Solomon and Johnson 2000).
• Easily observable traits such as skin color, earlobe structure, and hairline (e.g., widows’ peaks) can be used as examples for discussing variation among siblings and the genetic contribution of both parents to the trait.
• In middle school, combine learning about inherited traits with learning about sexual reproduction.
• Use caution with terminology when teaching genetics, particularly with the concept of dominance so as not to imply the idea that some genes are “strong” and some are “weak.” It may be better to say that dominant traits are expressed over recessive traits.
• Genetics terminology may hinder conceptual learning when terms are used imprecisely. If students are told, “Inherited traits are carried on chromosomes,” they may then confuse the terms trait and gene. Genes, not traits, are carried on chromosomes, and traits are the expression of a gene combination. Clear and consistent use of terms such as trait, gene, and allele is essential for constructing an accurate conceptual foundation of genetics (Bryant 2003).
• Caution should be used when students are asked to develop or use models to represent the mechanism of inheritance. Some models oversimplify the process of random assortment, recombination, and pairing of genes and expression of traits. For example, modeling gene combinations and predictions with Punnett squares oversimplifies some inherited traits. As Bryant (2003) explains,
  
  The Punnett square works well for studying the inheritance of genetic traits controlled by a single gene, and can even be applied when two or more traits are considered simultaneously, as long as the genes are not located on the same chromosome (linked). Students often learn to use Punnett squares to obtain correct answers to genetics problems, but they fail to understand that a Punnett square represents two biological processes—gamete formation and fertilization. Students rely on Punnett squares as algorithms for getting the “right answer,” often at the expense of meaningful conceptual understanding.” (p. 11)
• During middle school and in high school, students transition from understanding that genes give instructions for traits to understanding that genes are instructions (“recipes”) for proteins and that proteins carry out the functions that result in traits. The instructional goal is for students to know why proteins are important.