Biology, Quarter 3, Unit 3.1 Chromosomes and...

Cumberland, Lincoln, and Woonsocket Public Schools, with process support from the Charles A. Dana Center at the University of Texas at Austin

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Biology, Quarter 3, Unit 3.1

Chromosomes and Inheritance

Overview Number of instructional days: 14 (1 day = 50 minutes)

Content to be learned Science processes to be integrated • Describe the structure of DNA as a way to

demonstrate an understanding of the molecular basis for heredity.

• Diagram or model the relationship between chromosomes, genes, and DNA, including histones and nucleosomes.

• Distinguish the stages of mitosis and meiosis and how each contributes to the production of offspring with varying traits.

• Explain how alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism.

• Understand how humans are affected by environmental factors such as radiation or chemicals and how such factors can cause gene mutations.

• Predict, question, and hypothesize.

• Use tools and techniques to collect data.

• Represent, analyze, and interpret data.

• Use evidence to draw conclusions.

• Communicate understanding and ideas.

• Describe how structure affects function.

• Examine patterns of change.

Essential questions • What are the major components of DNA? How

do the components relate to the overall function of DNA?

• How does diagramming or modeling explain the relationship among chromosomes, genes, and DNA, including histones and nucleosomes?

• How can alteration of chromosomes produce changes that could enhance capabilities or be harmful to the organism?

• How can environmental factors cause gene mutations in humans?

• How can mitosis and meiosis each contribute to the production of offspring with varying traits?

• How does meiosis result in a great variety of possible gene combinations and contribute to natural selection?

Biology, Quarter 3, Unit 3.1 Chromosomes and Inheritance (14 days)


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Written Curriculum

LS1 - All living organisms have identifiable structures and characteristics that allow for survival (organisms, populations, & species).

LS1 (9-11) FAF+ POC -2 Explain or justify with evidence how the alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism (e.g., selective breeding, genetic engineering, mutations).

LS1 (9-11) –2 Students demonstrate an understanding of the molecular basis for heredity by …

2a describing the DNA structure and relating the DNA sequence to the genetic code.

LS1 (Ext) –2 Students demonstrate an understanding of the molecular basis for heredity by …

2aa diagramming or modeling the relationship between chromosomes, genes and DNA, including histones and nucleosomes.

LS3 - Groups of organisms show evidence of change over time (structures, behaviors, and biochemistry).

LS3 (9-11) INQ POC-7 Given a scenario, provide evidence that demonstrates how sexual reproduction results in a great variety of possible gene combinations and contributes to natural selection (e.g., Darwin’s finches, isolation of a species, Tay Sach’s disease).

LS3 (Ext) -7 Students demonstrate an understanding of Natural Selection/ evolution by…

7aa distinguishing the stages of mitosis and meiosis and how each contributes to the production of offspring with varying traits

LS 4 - Humans are similar to other species in many ways, and yet are unique among Earth’s life forms.

LS4 (9-11) NOS+INQ -9 Use evidence to make and support conclusions about the ways that humans or other organisms are affected by environmental factors or heredity (e.g., pathogens, diseases, medical advances, pollution, mutations).

LS4 (9-11) –9 Students demonstrate an understanding of how humans are affected by environmental factors and/or heredity by …

9a researching scientific information to explain how such things as radiation, chemicals, and other factors can cause gene mutations or disease.



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Clarifying the Standards

Prior Learning

In grades K–4, students learned that plants and animals need resources to reproduce. They labeled and used pictures to sequence the stages in life cycles of plants and/or animals. Students observed changes and recorded data to scientifically draw and label the stages in a life cycle of a familiar plant or animal.

In grades 5 and 6, students compared and contrasted asexual and sexual reproduction. They defined reproduction as a process through which organisms produce offspring. Students described reproduction as being essential for the continuation of a species. They also compared a variety of plant and animal life cycles.

By grades 7 and 8, students furthered their understanding to include genetics. They described and gave examples of various types of asexual reproduction (e.g., binary fission, fragmentation). Students learned that sexual reproduction involves the combination of genetic material from two parents (e.g., egg/sperm). They described the major changes that occur over time in human development from single cell through embryonic development to newborn. Students demonstrated this by identifying the stages of human embryonic development and describing the changes from one stage to the next. They compared and contrasted embryonic development in various life forms (e.g., humans, chickens). Students compared the patterns of human development after birth to life stages in other species.

Current Learning

The level of instruction for this unit is both developmental and reinforcement of previous knowledge. Students demonstrate an understanding of the molecular basis for heredity by describing the structure of DNA. They accomplish this by diagramming or modeling the relationship among chromosomes, genes, and DNA, including histones and nucleosomes. Students explain how alterations in chromosomes may cause changes that make little difference, enhance capabilities, or can be harmful to the organism.

After establishing this foundational knowledge of DNA structure and packaging, students distinguish the stages of mitosis and meiosis and how each contributes to the production of offspring with varying traits. Given a scenario, students provide evidence that demonstrates how sexual reproduction results in a great variety of possible gene combinations.

Students are expected to predict, question, and hypothesize possible outcomes of alteration to the DNA sequence and/or errors that could occur during mitosis/meiosis. They use tools and techniques to collect data regarding the stages of mitosis/meiosis. Students then represent, analyze, and interpret data, using evidence to draw conclusions about cycles (life cycle of cells and/or life cycle of multicellular organisms) in the natural world.

Early in this unit, students need to establish a clear understanding of the structure and packaging of DNA. Students apply this knowledge as they learn the cell cycle, in particular when they learn about DNA replication prior to mitosis and meiosis. During this unit, students should use their knowledge of DNA structure to understand DNA replication. This knowledge could then be applied to diagram or model a chromosome and to understand the relationship between DNA and chromosomes. As the unit progresses, students apply their knowledge of chromosomes to understanding the stages of mitosis and meiosis. Students could use microscopes with prepared slides of a plant (e.g., onion root tip) or animal (e.g., whitefish blastula) or view images online or otherwise. In terms of mitosis, they should understand that without mutations the resulting daughter cells are identical (clones). This could be modeled using beads,



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pipe cleaners, etc. Students should learn about cancer and its relationship to the cell cycle. There are many different ways to introduce this, from viewing slides to investigating checkpoints in interphase. There are even several short videos available that help students to understand and make connections to real-life situations dealing with cancer. In terms of meiosis, the resulting daughter cells are not only haploid, but also contain a variety of gene combinations due to independent assortment and crossing over. This could also be modeled using the same materials. Students should also understand that the combination of two haploid cells (gametes) results in additional genetic variation—making sexual reproduction a tremendous source of genetic variety with contributes to natural selection. To wrap up this unit, it might be helpful to allow students the opportunity to compare and contrast these two processes. This could be done in groups or independently though a product such as a poster, brochure, or other visual.

During this unit, students should begin to understand the role of mutations in both mitosis and meiosis. This is a good opportunity to introduce the difference between basic DNA mutations (point, frameshift, etc.) and chromosomal mutations (nondisjunction, translocation, etc.). However, they will learn about mutations formally in Unit 3.2 of this course. At this time, students should learn how environmental factors such as radiation or chemicals could result in such mutations.

Coming into high school, students have a basic understanding of genetic material—knowing that it is housed in the nucleus of a (eukaryotic) cell. They have an understanding of asexual versus sexual reproduction, but not at the molecular level. This is the main focus in high school biology—understanding the nature of DNA and chromosomes and their role in reproduction.

Future Learning

In Unit 3.2, students will explore how DNA can be altered and how this affects genes and heredity. They will apply their knowledge of DNA structure to transcription and translation, looking more specifically at genes and their resulting proteins. Students will also apply this foundational knowledge to their future understanding of selective breeding, genetic engineering, and how genetic mutations occur.

Students will rely on the knowledge from this unit throughout upcoming units. They will apply this foundational knowledge in their study of DNA to protein, genetics, and evolution. If students have not yet taken chemistry, they will use their knowledge of hydrogen bonds, covalent bonds, and biological molecules during the course.

Additional Findings

Although implied, it is not clearly stated that students must understand DNA replication. However, to understand the structure of a chromosome, they must understand that DNA has been copied and further that the cell cycle consists of more than just mitosis/meiosis (interphase and cytokinesis must be addressed).

“The same genetic information is copied in each cell of the new organism” is shown as prior knowledge (to cell division/reproduction) on pp. 69, 71, 73, and 75 of Atlas of Science Literacy, Vol. I. Complex interactions among the different kinds of molecules in the cell cause distinct cycles of activities such as growth and division. (p. 73) Commonly held ideas about mutation often carry some misconceptions, such as the whole organism can mutate during their own lifetime. Although this is not inconceivable, it is not what is usually meant by mutation and is irrelevant to the origin of variation and heredity. (p. 70) There are several incorrect ideas among middle and high school students regarding sexual reproduction. Students often equate sexual reproduction with copulation (e.g., many students consider in vitro fertilization an example of asexual reproduction). They do not understand that sexual reproduction is the



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fusion of specialized cells from two parents that does not necessarily require physical contact between the parents. Students often also assume that males of all species are larger and stronger than females and that the offspring produced by asexual reproduction are weaker than those produced by sexual reproduction. Students also assume that mutation and recessive have negative connotations.

Using a modeling activity for meiosis that begins with a small set of chromosomes, introduces students to crossing over, and ends after fertilization can help students recognize that genes are discrete entities inherited from both parents. (The Biology Teacher’s Handbook, 4th Edition, pp. 49 and 50)

Students do not believe that plants are capable of sexual reproduction. Asexual reproduction was thought to be restricted to microorganisms.

Students recognize that variation between species occurs, but regard it as a response to environmental conditions—rather than due to inheritance.

Lack of a precise concept distinguishing sexual reproduction from asexual reproduction appears to preclude an understanding of the origins of variation.

Sexual reproduction is not recognized as a source of genetic variation within a population. There was a study done (with 15 year olds) in which only 1 percent of students gave an accurate explanation of variation, correctly involving reproduction.

Several researchers have found that pupils, even before specific teaching, know the word gene and less frequently chromosome. However, pupils appear to understand little of the nature or function of genes and chromosomes, not appreciating that there is a chemical basis to inheritance. (Making Sense of Secondary Science, pp. 50–52)



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DNA to Protein


Content to be learned Science processes to be integrated • Demonstrate an understanding of the molecular

basis for heredity by relating the DNA sequence to the genetic code.

• Describe how DNA contains the code for the production of specific proteins.

• Trace in a diagram/model the information flow—from DNA to RNA to protein—through the processes of transcription and translation.

• Explain how DNA may be altered and how this affects genes/heredity.

• Create, analyze, and interpret diagrams/ models.

• Use evidence to draw conclusions.


• Describe how the structure affects function (form/function).

• Examine patterns of change.

Essential questions • At the molecular level, how do DNA sequences

relate to an organism’s genes?

• Why are the processes of transcription and translation necessary for the production of proteins?

• In what ways can the DNA sequence be altered? How could this affect genes/heredity?

• Explain/justify how the alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism.

Biology, Quarter 3, Unit 3.2 DNA to Protein (14 days)


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Written Curriculum

LS1 - All living organisms have identifiable structures and characteristics that allow for survival (organisms, populations, & species).

LS1 (9-11) FAF+ POC -2 Explain or justify with evidence how the alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism (e.g., selective breeding, genetic engineering, mutations).

LS1 (9-11) –2 Students demonstrate an understanding of the molecular basis for heredity by …

2a describing the DNA structure and relating the DNA sequence to the genetic code.

LS1 (9-11) –2

2c describing how DNA contains the code for the production of specific proteins.

LS1 (Ext) –2

2cc tracing in a diagram or model the information flow - DNA to RNA to Protein - through transcription and translation.

LS1 (9-11) –2

2b explaining how DNA may be altered and how this affects genes/heredity (e.g. substitution, insertion, or deletion).


Prior Learning

In grades K–4, students sequenced the life cycle of a plant or animal when given a set of pictures.

In grades 5 and 6, students defined reproduction as a process through which organisms produce offspring. They described reproduction in terms of being essential for the continuation of a species. Students investigated and compared a variety of plant and animal life cycles.

In grades 7 and 8, students explained how each type of cell, tissue, and organ has a distinct structure and set of functions that serve the organism as a whole. They were exposed to the fact that in human cells the nucleus contains genetic material (i.e., genes and chromosomes). Students learned that genetic material is passed from parent(s) to offspring and that this is related to the traits that organisms have (e.g., eye color, skin color). They also learned that genetic changes affect survival.

Current Learning

The instructional level of this unit is primarily developmental, as most information is new. Students demonstrate an understanding of the molecular basis for heredity by relating the DNA sequence to the genetic code. This might be accomplished through first revisiting the structure of DNA (from the previous



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unit) and then applying that knowledge to a new understanding of DNA sequence as it relates to genetic code. It is important that they understand how the molecular structure affects its function. Students then describe how DNA contains the code for the production of specific proteins. Many teachers help students make a connection between the terms chromosome, gene, and protein. Diagrams and models are exceptionally useful in accomplishing this.

Students should produce diagrams/models that provide information about the information flow—from DNA to RNA to protein—through the processes of transcription and translation. Again diagrams and models are quite helpful in accomplishing this. For example, students could create paper models, use computer simulations, use manipulatives such as Kinex, or other forms of hands-on learning activities. Through these activities, students should be able to begin with a sequence of DNA, transcribe this code into mRNA, translate the mRNA into a sequence of amino acids (using the chart/wheel), and understand that a chain of amino acids constitutes a protein.

Once students understand protein synthesis, they should explain how DNA may be altered and how this affects genes/heredity. This is the time to introduce the different types of mutations (e.g., insertion, deletion, substitution). Students should be able to explain/justify how the alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism.

During this unit of study, it is important for students to have the opportunity to create, analyze, and interpret diagrams/models. The processes and concepts learned here are quite abstract and traditionally difficult for students to grasp. Modeling allows students to visualize these processes and then communicate their understanding and ideas about genetic sequences and proteins.

Students should be able to describe how the molecular structure of DNA affects its function in the production of proteins. Based on their understanding of the structure of DNA, students should draw conclusions based on evidence about the relationship between form and function in the natural world.

Students should examine patterns of change in this unit, as they pertain to alterations in the DNA sequence and possible outcomes of these changes/mutations.

In the classroom, students are engaged in active learning—through the creation and/or manipulation of physical models or use of computer models/simulations. Students analyze DNA sequences and synthesizing chains of amino acids. Later in the unit, they analyze various alterations/mutations to DNA sequences and observe the affects (if any) on the resulting protein.

In this unit of study, students examine the molecular basis for heredity—a concept that has not been previously addressed in other grades. They were exposed to the fact that the nucleus contains genetic material for heredity, this genetic material is inherited, and alterations to genetic material can affect survival. However, they have not yet learned about the molecular structure of DNA and how this structure affects its function. This unit allows students to make connections between genetic traits and the molecular basis of heredity.

Future Learning

This unit is foundational for the next unit, Genetics. It is also extremely important to Unit 4.1, Evolution. In Genetics, students explore many topics that require a prior understanding of protein synthesis. Without the knowledge from this unit, students will not be able to understand the sorting and recombination of



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genes in sexual reproduction or how environmental factors such as radiation or chemicals can cause gene mutations or disease.

When studying the concept of evolution, students need this prior knowledge to fully understand microevolution or macroevolution. Biodiversity, as a result of these, will be very difficult to learn without knowledge of how genes code for proteins—which ultimately may affect survival and reproduction.

The knowledge acquired in this unit will be helpful to students that pursue future life science courses such as forensics, biotech, anatomy, and physiology. The processes used during this unit could be applied to any future course.

Additional Findings

Several researchers have found that pupils, even before specific teaching, know the word gene and less frequently chromosome. However, pupils appear to understand little of the nature or function of genes and chromosomes, not appreciating that there is a chemical basis to inheritance. (Making Sense of Secondary Science, p. 52)

Basic literacy does not require explaining the structure and function of DNA beyond it being a molecular string of genetic code that directs the assembly of proteins. (Advanced students could certainly learn more about the details once the literacy base is established.) (Atlas for Science Literacy, Vol. 1, p. 68)

Commonly held ideas about mutation often carry some misconceptions, such as whole organisms can mutate during their lifetimes. Although this is not inconceivable, it is not what is usually meant by mutation and is irrelevant to the origin of variation in heredity. (Atlas for Science Literacy, Vol. 1, p. 70)

Students’ growing notion of systems can help them understand how turning instructions on and off can sequence developments over a lifetime and that each cell’s immediate environment can influence its development, even though nearly all cells carry the same DNA instructions. (Benchmarks for Science)


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Genetics


Content to be learned Science processes to be integrated • Investigate how information is passed from

parents to offspring by encoded molecules.

• Investigate how the sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations in the offspring of any two parents.

• Research how scientific information explains how such things as radiation, chemicals, and other factors can cause gene mutations or disease.

• Observe, predict, question, and hypothesize.


• Represent, analyze, and interpret data.

• Use data models.

• Use evidence to make and support conclusions.

• Observe patterns of change over time.

• Conduct scientific research.

Essential questions • How does sexual reproduction result in a great

variety of possible gene combinations from any two parents?

• How can the sorting and recombination of genes in sexual reproduction contribute to natural selection?

• How are encoded molecules involved in passing information from parents to offspring?

• How can heredity cause disease?

• How can environmental factors cause mutations or diseases?

Biology, Quarter 3, Unit 3.3 Genetics (14 days)


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Written Curriculum

LS3 - Groups of organisms show evidence of change over time (structures, behaviors, and biochemistry).

LS3 (9-11) INQ POC-7 Given a scenario, provide evidence that demonstrates how sexual reproduction results in a great variety of possible gene combinations and contributes to natural selection (e.g., Darwin’s finches, isolation of a species, Tay Sach’s disease).

LS3 (9-11) -7 Students demonstrate an understanding of Natural Selection/ evolution by…

7a investigating how information is passed from parents to offspring by encoded molecules (e.g. evidence from electrophoresis, DNA fingerprinting).

7b investigating how the sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations in the offspring of any two parents. (e.g. manipulate models to represent and predict genotypes and phenotypes, Punnett Squares, probability activities).

LS 4 - Humans are similar to other species in many ways, and yet are unique among Earth’s life forms.

LS4 (9-11) NOS+INQ -9 Use evidence to make and support conclusions about the ways that humans or other organisms are affected by environmental factors or heredity (e.g., pathogens, diseases, medical advances, pollution, mutations).

LS4 (9-11) –9 Students demonstrate an understanding of how humans are affected by environmental factors and/or heredity by …

9a researching scientific information to explain how such things as radiation, chemicals, and other factors can cause gene mutations or disease.


Prior Learning

In grades K–4, students distinguished between characteristics of humans that are inherited from parents (e.g., eye color, skin color) and others that are learned (e.g., playing a piano, riding a bike). They demonstrated an understanding of heredity by observing and comparing their own physical features with those of parents, classmates, and other organisms. Students recognized similarities that are inherited from a biological parent and identified that some behaviors are learned and some are instinctive.

In grades 5 and 6, students used evidence provided to select evidence that supports the concept that genetic information is passed on from both parents to offspring. They differentiated between acquired and inherited traits. Students observed, recorded, and compared differences in inherited traits (e.g., tongue rolling, attached earlobes).



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In grades 7 and 8, students recognized that some characteristics are the result of inherited traits from one or more genes passed from parents, while other characteristics are the result of environmental factors. They traced a genetic characteristic through a given pedigree to demonstrate the passage of traits (e.g., Queen Victoria and hemophilia). Additionally, students should have understood that the genetic material (i.e., chromosomes and genes) is located in the cell’s nucleus (specifically for a human).

Current Learning

The instructional level of this unit is primarily reinforcement. However, when investigating how the sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations, it is important to begin instruction at the introductory level and end at drill and practice.

In this unit, students investigate how information is passed from parents to offspring by encoded molecules. They also investigate how the sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations in the offspring of any two parents. It is important that students understand how the sorting and recombination of genes in sexual reproduction contributes to natural selection, although this is only introduced in this unit. The next unit of study, Evolution, will fully address natural selection as the mechanism for evolution.

Finally, students should research how human disease can be caused by heredity.

In this unit, students observe, predict, question, and hypothesize about the possible outcomes of genetic crosses and patterns of inheritance. They represent, analyze, and interpret data, including the use of Punnett squares. Students use evidence to make and support conclusions based on the outcomes of genetic crosses. They should be able to communicate understanding and ideas about inheritance patterns and probabilities.

During this unit, they learn about the history of Mendelian genetics and the importance of scientific process and problem solving. They are introduced to natural selection and patterns of change in inherited characteristics over time. Students should have the opportunity to research a genetic disease and communicate their understanding of this condition.

Through the use of Punnett squares, students predict genetic outcomes. Many teachers use this as an opportunity to explore various patterns of inheritance (e.g., complete dominance, codominance, incomplete dominance, sex-linkage, multiple alleles). It is important that students make the connection that sexual reproduction leads to genetic variation and diversity, therefore allowing for natural selection to occur.

Once students have mastered genetic probabilities and understand the mechanism of inheritance, they research a genetic disorder and communicate current understandings and ideas. This might be accomplished through PowerPoints, posters, presentations, or scientific writing. As scientific literacy is a goal in all schools, this research provides an excellent opportunity for students to write. At this time, they can apply their prior knowledge regarding media bias and validity of sources to complete a more formal product.

In previous grades, students learned that traits are passed from both parents to offspring. However, they did not predict the outcomes or calculate probabilities of genetic crosses. Additionally, students never explored the importance of sexual reproduction and its effects on genetics. Although students explored pedigrees to examine what has happened in a family lineage, they did not explore what could happen in encoded molecules to produce diversity.



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In addition, this is students’ first chance to conduct scientific research using their new (current year) knowledge of media bias and validity of sources.

Future Learning

This knowledge will provide a foundation for the study of evolution. Genetic diversity is essential for natural selection to occur, and in this unit students learned about the source of genetic diversity. One component of the Evolution unit is microevolution, during which students will explore allele frequencies and how many times phenotypes/genotypes determine survival.

During the last unit of the school year, Classification of Life, students will revisit the use of evidence from encoded molecules to determine relatedness.

The research and scientific literacy component of this unit could be applied to any future unit or course.

Additional Findings

Some students believe that traits are inherited from only one parent (e.g., traits are inherited from the mother because she gives birth or has most contact as children grow up; the same sex parent is the determiner). Some students believe that certain characteristics are always inherited from the mother and others come from the father. Some students can use arguments based on chance to predict the outcome of inherited characteristics of offspring from observing those characteristics in the parents. (Atlas for Science Literacy, Vol. 1, p. 68)

Pupils have some idea of the randomness of inheritance—that sometimes offspring are like their mother, sometimes like their father, and sometimes both. However, pupils rarely showed evidence of applying the concept of chance and probability to inheritance and evolution. The concepts of randomness and probability are not held by many students even after advanced courses. Hickman et al. found that many could predict mathematical probabilities of outcomes in isolated theoretical examples but could not do this with examples of situations in human families. (Making Sense of Secondary Science, p. 53)

Students invariably attribute observable variation to environmental factors alone. Sexual reproduction is not recognized as the source of variation in a population … [in a study] only 14 percent mentioned sexual reproduction or natural variation, even though the question said that environmental conditions were kept constant. Only 1 percent gave an accurate explanation of variation, correctly involving reproduction. (Making Sense of Secondary Science, p. 52)

One of the many misunderstandings of probability that teachers have to deal with is that a well-established probability will be changed by the most recent history: People tend to believe that a coin that has come up heads 10 times in a row is more likely on the next flip to come up tails than heads. (Benchmarks for Science Literacy, p. 226)

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