(1) There is generally limited empirical evidence that suggests which intermediate ideas are productive stepping stones at each level. We have, however, evidence that students can develop these ideas (citations noted). Also, these intermediate understandings address ideas for which we have some informed hypotheses that lead to the important ideas in the targeted understanding. In many cases to move from an intermediate understanding to the targeted level of understanding all connections between ideas need to be consistently made.
(2) Again the three models and five core ideas are represented in the storyline. These need to be connected in order to reach proficiency.
(3) In many cases there is little insight into student’s early ideas about genetics that are building blocks to later understanding. There is, however, research on naive conceptions, some of which occur after students have some initial exposure to concepts in genetics.
(4) The notion of information as being passed on is not emphasized in most early curricula. "Information" at this level is about influencing the development of traits or perhaps even how cells or organs function.
(5) Perhaps because students believe “inheritance” is passed on through the blood (a “blood relative”); Actually, mature mammalian red blood cells lack of nuclei and organelles, do not contain DNA and cannot synthesize any RNA, and so cannot divide and have limited repair capabilities,.
(6) The idea that genes are informational is key. The basis for understanding how genes bring about physical traits lies in an understanding of genes as instructions for proteins. Students need to develop basic understandings of the kinds of functions proteins have in cells in middle school. LIMIT: They do not need to understand the chemical structure of proteins, but they should come to view proteins as “little machines” that either do work, or are structural components of the cell. Students will not be able to advance on many of the concepts without these understandings.
(7) While “genes-as-particles” is not accurate, this thinking can be useful as long as students can build from it and this idea is confronted later in school.
(8) LIMIT: rare exceptions like mature red blood cells do not contain DNA or RNA.
(9) Chromosomes are viewable under a microscope and this can help anchor students’ understandings of the ideas of chromosomes, genes, and later DNA.
(10) LIMIT: but not yet describe molecular mechanisms consistently. There is some evidence that with appropriate instruction students can connect genes to protein function (Duncan, unpublished results).
(11) LIMIT: Localization to nucleus is not essential, but can be covered if issues like cloning will be addressed.
(12) There is little current evidence for the particular intermediate stepping stones here; these are informed hypotheses.
(13) Students need to understand cells as the basis of life in order to understand concepts related to cell division. There is little current evidence for the particular intermediate stepping stones here; these are informed hypotheses.
(14) Many students fail to connect cell division to passage of genetic information (Lewis and Wood-Robinson, 2000) or recognize the importance of duplication of genetic materials (Riemeier & Gropengiesser, 2007). Students must make connections between these elements before high school.
(15) The idea that we have 2 versions of each gene (two alleles) because we have homologous chromosomes is at the crux of understanding the three genetic models. This is in no way obvious or intuitive (why have 2 when you can get by with one?). It may not hold for all organisms but it holds for ones students are familiar with. Without an understanding of the duplicate copies of genes they cannot understand meiosis or classical genetics. This should be introduced concurrently with the idea of halving the genetic information in sex cells.
(16) Rather than a focus on the details of the process (the multitude of steps) there should be explicit attention to the purpose and outcome of these processes and how this relates to the organism’s stage in the life cycle. Learning them out of this context is confusing for students as they don’t see a purpose to these processes.
(17) LIMIT: recombination is not part of this understanding until high school.
(18) Students likely will not, however, consider how the thousands of genes together influence all the inherited traits and critical life functions.
(19) LIMIT: students do not need to understand the details of DNA replication (transcription and translation).
(20) LIMIT: students do not need to explain how the numbers of chromosomes or genes are preserved through the division process.
(21) Genomic scientists have a good estimate of the number of genes in the human genome as a result of the human genome project (the current estimate is 20,000-25,000 genes), but students do not need know the specific number. It is enough that they know the estimate to be tens of thousands of genes.
(22) Recent evidence suggests middle school students can get to the molecular or cellular level (Duncan, unpublished results).
(23) LIMIT: we would not expect students to understand the molecular nature of DNA at this age.
(24) LIMIT: but do not connect to concept of alleles until high school.
(25) This belief seems particularly problematic to developing ideas about the segregation and random assortment of alleles in high school.
(26) The Punnett square technique should not be the learning performance; the ability to think about potential genetic combinations and use that that to make predictions about the occurrence of future phenotypes is the goal. Meiosis has to be connected to the resulting effects on the distribution of chromosomes and genes (Lewis and Wood-Robsinson, 2000) and to these Punnett square problems in order for students to “meaningfully” engage in these problems (Stewart, 1982).
(27) Students tend to attribute outcomes of an event that occurs due to random chance as the result of some causal or directive agent (Klymkowsky & Garvin-Goxas, 2008). This may prevent them from incorporating ideas about random and independent assortment to the distribution of alleles between generations.
Authors and Reviewers
Dr. Aaron Rogat, Teachers College, Columbia University and the Consortium for Policy Research in Education (CPRE), New York (author)
Dr. Ravit Duncan, Rutgers University, New Jersey (reviewer)
Allchin, D. 2002. "Dissolving Dominance." Pp. 43-61 in Lisa Parker and Rachel Ankeny (eds.), Mutating Concepts, Evolving Disciplines: Genetics, Medicine, and Society. Dordrecht: Kluwer.
Banet, E., & Ayuso, E. (2000). Teaching genetics at secondary school: A strategy about teaching the location of inheritance information. Science Education,84, 313-351.
Consortirum for Policy Research in Education (CPRE). (2008) Science PCK Tool. (2008). University of Pennsylvania: CPRE, Philadelphia.
Duncan, R.D, Rogat, A.D., & Yarden, A. (2009) A Learning Progression for Deepening Students’ Understandings of Modern Genetics Across the 5th-10th grades. Journal of Research in Science Teaching. 46(6): 655-674.
Flores, F., Tovar, M., & Gallegos, L. (2003). Representation of the cell and its process in high school students: An integrated view. International Journal of Science Education, 25(2), 269-286.
Klymkowsky, M.W. & Garvin-Goxas, K. (2008, January). Recognizing Student Misconceptions through Ed's Tools and the Biology Concept Inventory. PLoS Biology. 6(1)e3.
Lewis, J. & Kattmann, U. (2004). Traits, genes, particles and information: Revisiting students' understanding of genetics. The International Journal of Science Education, 26, 195-206.
Lewis, J., & Wood-Robinson, C. (2000). Genes, chromosomes, cell division and inheritance -- do students see any relationship? International Journal of Science Education, 22, 177 - 195.
Lewis, J., Leach, J. & Wood-Robinson, C. (2000). All in the genes? - Young people's understanding of the nature of genes. Journal of Biological Education, 34, 74-79.
Marbach-Ad, G., & Stavy, R. (2000). Students cellular and molecular explanations of genetic phenomena. Journal of Biological Education, 34, 200-210.
National Research Council. (2007). Taking science to school: Learning and teaching science in grades K-8. Washington DC: National Academy Press.
Riemeier, T., & Gropengiesser, H. (2007). On the roots of difficulties in learning about cell division: Process-based analysis of students’ conceptual development in teaching experiments. International Journal of Science Education,7, 1-17.
Rogat, A., & Krajcik, J. (n.d.). Unpublished results.
Shaw, K.R,M., Van Horne, K., Zhang, H. and Boughman, J. (2008). Essay Contest Reveals Misconceptions of High School Students in Genetics Content. Genetics, 178, 1157–1168.
Stewart, J. (1982). Difficulties Experienced by High School Students when Learning Basic Mendelian Genetics. The American Biology Teacher. 44(2), 80-89.
Venville, G., Gribble, S., & Donovan, J. (2005). An Exploration of Young Children’s Understandings of Genetics Concepts from Ontological and Epistemological Perspectives. Science Education. 89(4), 614-633.
Concept and Skill Progression forEvolution & Biodiversity The progression is organized in four core ideas: fossils, morphology, and DNA can provide evidence of common ancestry among organisms; a species needs genetic variation to survive and adapt; populations change due to natural selection and adaptation of many individuals; and biodiversity results from the formation of new species.
Before instruction students know there are different environments where animals and plants live.
Conceptual Stepping Stones
Early Elementary school students are able to observe and describe individual organisms and notice and describe qualitative variation within a population. Students are aware that there are different environments with different climates that are home to specific types of animals and may be able to describe some characteristics of the animal that allow it to live in that environment. They understand that fossils are evidence of animals and plants that lived long ago. Students are able to observe organisms and their attributes and can describe changes brought about by growth. The can distinguish stages of growth of certain organisms. Children can measure heights of plants and lengths of caterpillars, use Venn diagrams to reason about similarities and differences between moths and beetles, and represent change by successive differences of measures.
Late elementary school students understand that individuals of the same kind differ in their characteristics, and sometimes the differences give individuals an advantage in surviving and reproducing. Students understand that structures perform functions that allow individuals to survive. Students can relate qualities of habitat and attributes of the organisms living there. Students understand that changes in an environment can be detrimental to the organisms within it. Students make comparisons between characteristics of fossils and those of living organisms and can infer what the environment was like of the organisms that lived long ago. Students engage in forms of argument that include comparative analysis and modeling. Students are able to interpret change as difference between two measures: They can compare net change in more than one individual and coordinate descriptions of change in counts or measures on two or more organisms or within attributes of the same organism. Students now include microorganisms as living entities. Students can describe change over time mathematically (rate and changing rates) and characterize a measure (including units) based on a selected attribute.
Middle school students understand that biodiversity consists of different life forms (species) and they understand Earth consists of many biomes and ecosystems that support and have influence on this variety of life. At this age students can distinguish between attributes and characteristics that are inherited through sexual or asexual reproduction and those that are environmental. Students can explain how natural selection arises. Students understand that species that inhabit different habitats can have genetic variation, and they understand species can change over generations and attribute this change to the specific beneficial traits of the individuals that survived to reproduce. Students understand chronology and sedimentary rock deposition and relate placement of the fossil in the sedimentary layer to its age. Students are able to use mathematical and graphical constructs to compare competing models of observed distribution and are able to relate statistics describing the distribution to biological events or processes and are able to develop competing models for the same distribution of observed values. Students can interpret a graph or table of rate of change and are able to describe change using these measures.
High school students understand that organisms reproduce to allow for the passing on of traits to successive generations. They understand that sexual reproduction provides a source of genetic variation and can describe the various ways in which genetic variation comes about. They can explain that those individuals with characteristics that provide them with some reproductive advantage over others in that particular environmental situation will survive to reproduce, whereas others will die. Students are able to explain that not all offspring survive to reproductive age in part because of competition for resources. Students understand the relationship between biodiversity and extinction. They understand what alleles are and how populations can change over time as frequencies of advantageous alleles increases. Students understand that natural selection can occur only if there is variation in the genetic information between organisms of the same species in a population and variation in the expression of that genetic information as a trait. They are able to explain that the similarities and differences in DNA sequences, anatomical evidence, and fossil evidence provide information about the branching sequence of lines of evolutionary descent. They understand that advanced technologies have allowed scientists to compare DNA sequences of various organisms to infer lines of descent. Their methods of classification are more sophisticated and so they are able to characterize various organisms as species and then classify species of organisms in groups (taxa) called clades to illustrate their common ancestry. Students are able to provide a rational argument of how biological evolution explains the unity and diversity of species.