Before instruction, students often believe and can:
Students who view the world in this way believe and can:
Students who fully understand this topic believe and can:
Organization and location Possible Misconception:
While children will have likely heard of the terms DNA and genes from media, and might develop some associations with these (see below), they likely will think of them as separate entities (Venville et al, 2005) with separate functions.
Students are likely to have heard of “genes” and “DNA.” Students may believe that genes are associated with a theory of kinship (they might say “it makes me look like my parents”) and believe that DNA is a unique identification marker (such as for crime scene investigations so prevalent in media) (Venville et al, 2005).
Students may understand that all living things share something in common, but are likely to focus on physical attributes like the ability to respond, move, or grow (National Research Council, 2007) and are less likely to think of DNA or genes as common characteristics of all living organisms (A. Rogat, unpublished data)
Organization and location
Students can explain that genes are found somewhere inside of living organisms. Most students will know that mammals, and even reptiles and insects, have genes.
Students often believe a trait is the same as a gene (Venville et al, 2005). Students likely will not believe that plants (or other non-human organisms, such as bacteria or fungi; Shaw et al, 2008) have DNA or genes like humans do (Lewis et al, 2000; Venville et al, 2005). Students may also believe that non-living object such as computer, cars, or digital characters like Digiman have DNA (Venville et al, 2005).
Students can explain that genes provide “information” about the development of how things look (Venville et al, 2005). They might apply this claim to a limited number of organisms. Genes are seen as purely passing on information from one generation to another.4
Organization and location Students are able to explain that genes are inside cells of organisms, but may believe they are in only a few cell types like brain and blood cells (Banet & Ayuso, 2000).5 Students can identify genes in a broader class of organisms, including plants. Also able to distinguish the difference between a trait and a gene, in other words know that a gene corresponds to a physical entity inside of cells, and traits are physical characteristics of organisms that genes influence (e.g. “a gene for eye color" is not actually an eye color, but it influences the type of eye color that is observed in an animal's eye).
Students can explain that genes provide information that affects the development of physical characteristics (traits), protein structure and function, and cellular activities and functions.6
Students likely believe genes are active “particles” (Lewis & Kattman, 2004).7
Organization and location Students now understand that genes are found inside of all organisms and can associate genes with chromosomes. Students can identify genes in sex cells and many other somatic cell types like skin cells, muscle cells, and brain cells.8 Students now understand relative sizes of the entities (genes, chromosomes, cells), including molecular entities or those that cannot be seen with the unaided eye.9
[Link to PS atoms and molecules] Possible Misconceptions:
Students will likely confuse the relationships between cells, atoms and molecules (Flores et al, 2003). They will likely confuse the relationships between genes, chromosomes, proteins, and cells (Lewis et al, 2000; Marbach-Ad et al, 2000; Rogat & Krajcik, n.d.).
Students are able to think about genes in transmission of information as coding for proteins or other cellular molecules that carry out the work of cells and provide structure to cells.10
Organization, location and function of genes and DNA
Students can relate and distinguish the difference between DNA, nucleotides (and their essential chemical components), genes, and chromosomes in animal and plant cells. Students understand that DNA is a long chain of carbon-based molecules, of which specific chemical subunits (nucleotides) in this chain confer information. Students understand that the DNA is packaged into chromosomes.11 The chromosomes are passed on from one organism to another during reproduction, and thus genes are passed on from one generation to another.
Students recognize that all organisms, even those without a nucleus like bacteria, have DNA and genes.
Students can explain the role and function of genes in living organisms. The order of nucleotides in specific segments of DNA provides information on how to build cellular molecules, namely proteins, that do work in cells (this is "genetic information"). These segments of DNA are genes. Students must understand the relationship of genes to proteins and phenotypes (or variations in traits, such as dark or light colored skin, or the existence or absence of a disease such as sickle cell anemia) (Duncan et al, 2009).
Passage of genetic information
Students typically know that babies grow and are delivered from within a mother’s body; this insight helps to develop a theory of inherited kinship (Venville et al, 2005). Students are likely to know that progeny in animals can be raised inside of a mother’s “belly.”
Students at the age of 6 or 7 are likely to have a theory of kinship and can distinguish some inherited characteristics verses socially determined characteristics (such as language spoken or food and clothes preferences) (Venville et al, 2005), although such understandings are better with human characteristics. For example, students likely would know an Asian baby adopted by an Australian Caucasian couple is likely to grow up looking Asian as an adult, but likely to speak English and not an Asian language.
Students can identify some critical aspects of organisms required for living, such as ability to reproduce and take in food for growth (National Research Council, 2007).
Passage of genetic information
Students understand that genes (or genetic information) are passed from generation to generation, but do not understand how. They should have developed a theory of kinship (i.e. they understand that young organisms born from older organisms will grow up to look like older organisms, but some characteristics such as spoken language are socially determined).
Students can identify most of the critical aspects of living organisms, including the ability to reproduce, harvest energy from food, grow, and get ride of waste.
Students realize that cells divide to produce more cells; they do not just spontaneously appear.
Students typically fail to connect cell division to the passage of genetic information. The term "cell division" may lead students to develop a variety of models of cell growth – some of which preclude a model where the ending products have the same amount of material as the starting cell (CPRE, 2008). Students may associate reproduction with copulation. They may believe that it can only occur in animals (CPRE, 2008).
Passage of genetic information
Students can explain that chromosomes (which carry genetic information) are passed on from generation to generation during cell division (they relate kinship to genes or DNA).z4 Students understand that duplication of genetic information prior to cell division helps to maintain an equal amount of genetic information in future generations; students understand the mechanisms of how traits are passed between generations.
Students understand that for each trait we have two version of the gene (alleles).15
Students explain there are two types of cell division: mitosis occurs in most of the cells of the body, and meiosis occurs in only sex cells, like sperm and eggs. Students may not, however, properly connect these to specific cell types inside of living organisms (CPRE, 2008). They can, however, relate these to stages of the life cycle.16 Students can identify the relative amount of chromosomes or genes that result from mitosis and meiosis (e.g. sex cell produces cells each with half the complement of chromosomes or genes and other somatic cells produce two identical cells with a full complement of chromosomes or genes). They realize in sexual reproduction, egg and sperm fuse to produce a new cell that goes on to develop inside mother to become a new baby. Students realize that fertilization during sexual reproduction restores a full complement of chromosomes or genes.17 Students appreciate that sexual reproduction occurs in other organisms like plants. Explain that the existence of a cell indicates that another cell existed previously –cell division occurred which produced an identical cell.
[Link to gene functions] Genome
Students can associate physical traits and functions of an organism to genes. They recognize there are tens of thousands of genes that make up a genome in mammals.18
Passage of genetic information in living organisms through cellular reproduction
Students understand how an organism is able to pass on its physical characteristics to its offspring. Students can relate DNA duplication and nuclear division to the passage of DNA and consequently inherited traits. Students understand that DNA must be duplicated prior to cell division19; this means students must understand that a copy of the DNA molecule is made and subsequently the copy is passed on to a new cell (whether a new sex cell such as an egg cell or sperm cell or a new somatic cell such as a skin cell or an intestinal cell). As such, students understand the connection between chromosomes, genes, and DNA (when DNA is copied and passed on, so to are chromosomes that are made of DNA and the genes that reside on chromosomes). In this way the information in DNA can be passed on to future generations. Importantly in sexually reproducing multi-cellular organisms only the DNA in a sex cell (such as a sperm or egg cell) is of most importance when considering passage of heritable traits between parents and progeny, and less important is the DNA in somatic cells. However, the passage of genetic information from cell to cell occurs any time there is cell division in any somatic cell (such as a skin cell, a brain cell, or a muscle cell).
Students can predict the number of chromosomes or genes that a newly-divided cell will contain.20 Students understand that there are two types of division that cells can undergo (mitosis and meioses) and that these occur in different cell types and result in different numbers of chromosome or genes that are produced.
Students can explain why all the chromosomes in an organism have to be passed on to the next generation (whether a single-cell or multi-cellular organism). Students know that DNA must be duplicated and passed on so the function of genes (such as specifying proteins or other cellular molecules) can influence physical characteristics (Duncan et al, 2009). Students understand the nature and role of the genome: namely that all of the chromosomes and corresponding genes in an organism together influence all of the functions and behaviors that a living organism must carry out to live and survive, including basic functions like harvesting energy from food molecules, or building cellular molecules, or getting rid of cellular waste products.21
[Link to Cell Biology and Biochemistry]
The term “mutation” or “mutant” (from popular media) may have negative connotations or be associated with negative outcomes.
Students understand that mutations are changes in genetic information that can confer traits or functions that are not normal.
Students may believe mutations can perhaps do good.
Students understand that a mutation in a gene can result in a change in proteins which can influence cell function.22
[Link to gene functions and cellular reproduction]
Students understand the order of nucleotides in a gene determine the structure of a protein, and consequently the function of a protein in cells. Students can explain how a mutation in a gene can affect the structure, function, or behavior of a cell or an organism (i.e., its phenotype) by influencing the structure or function of cellular molecules such as proteins. Students can relate changes in protein function on cell function, structure, or behavior at the molecular level. Students understand that only mutations in gametes (i.e. egg and sperm in animals) are passed on to future generations.
[Link to genes, proteins, and phenotype]
Gene variation and phenotypes
Students know that some how genes are unique to a particular individual and can pass that on in order to pass on traits.
[Link to ‘traits can be passed on’ and ‘theory of kinship’]
Gene variation and phenotypes
Students can explain that gene sequences can vary23 and can be passed on to another generation, and can explain that different gene variations can affect protein or cell function.24
Dominant and recessive traits
Students may associate the terms “dominant” or “recessive” with specific functions. For example, Allchin (2002) notes the following beliefs regarding dominance:
• Dominant traits are “stronger” and “overpower” recessive traits.
• Dominant traits are more likely to be inherited.25
• Dominant traits are “better.”
• “Wild-type” or “natural” traits are dominant, whereas mutants are recessive.
• Male or masculine traits are “dominant.”
Gene variation and phenotypes as related to dominant and recessive traits
Students understand that the specific nucleotide sequences of genes vary, ranging from one small change in the nucleotide sequence to large changes. Student can apply their understanding about gene function to understand the molecular and cellular consequence of any changes to genes. Students can connect DNA sequence variation to the concept of alleles of genes, and connect this to the role of genes in influencing protein function, cell function, and phenotype.
Students can explain why a recessive allele cannot have an effect on the phenotype of an organism unless both alleles are of the same variation (homozygous), while a dominant allele can have an effect on the phenotype of an organism when only one allele is present (heterozygous). Students are also able to explain that the nature of the interaction is dependent on the type of variation in the gene sequence for each allele present– and that gene variations can result in abnormal, dysfunctional, or absent gene products. With this understanding, students can begin to explain the molecular basis for dominant or recessive alleles.
Patterns of inheritance
Students are likely to understand that sibling do not always look identical to each other or their parents, but may have a combination of traits.
Students are likely to believe that daughters get their traits from mothers, and likewise sons from fathers.
Patterns of inheritance12
Students understand that siblings do not always look identical to each other or their parents, but may have a combination of characteristics.
Patterns of inheritance
Students can predict all possible combinations of alleles (and potential phenotype) for the progeny of two parents with a given set of alleles and predict the frequencies of these combinations.26
Students can explain how events during cell division are important to why certain gene combinations are observed in predictable patterns. Students can apply ideas of random and equal distribution of alleles.27Students can explain that during sexual reproduction chromosomes can recombine and segregate in random ways, resulting in progeny that can have different combinations of alleles—and that this will determine the probability of occurrence for any particular allele combination, and consequently a particular phenotype.
[Link to gene variation, meiosis, cell division and passage of genetic information]