Next Generation Science Standards

Performance Expectation

Make and defend a claim based on evidence that inheritable genetic variations may result from: (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors.

• Clarification Statement: Emphasis is on using data to support arguments for the way variation occurs.
• Assessment Boundary: Assessment does not include the phases of meiosis or the biochemical mechanism of specific steps in the process.

This performance expectation asks students to learn the common sources of genetic variation by developing claims (hypotheses) then gathering evidence (data) to support their arguments. That means their theory that radioactive spider bites cause superpower mutations are about to be debunked. Bummer.

Students will be focusing their question-asking and hypothesizing skills on three specific tenets of inheritable genetic variation. Although they look straightforward enough, and we know they are indeed factual, the point here is for students to convince themselves through a careful examination of evidence/data from a variety of sources. Once they're convinced, then you can say, "I told you so. Neener, neener, neener!"

Here are some resources and activity ideas to throw variety into the gene pool of your classroom:

• Let's be realistic here. Your kids aren't seasoned researchers in high-tech labs. They're high school students in classrooms. They may have computers and modeling software, but probably not the equipment needed to test the sources of inheritable genetic variation. In the context of this performance expectation, discuss with students: what does defending a claim based on evidence actually mean? What are ways we can generate evidence without having a fancy lab? Are there any ways to test our hypotheses so we can use our own data to defend our claims? Even though they can't exactly be scientists, they can still think like scientists.
• It makes things way more engaging and interesting to tie in personal, relevant information from students' lives into your teaching, right? And it's even better when students can learn to navigate online databases—the same ones scientists use daily—to find data to solidify and back up their claims. When you think your students can handle something a little more challenging, give them this database of genetic conditions, and this one of various genes and their effects. Have students investigate the causes and effects of a genetic condition, asking questions along the way about the implications of mutations to important genes.
• The mighty PowerPoint presentation is a tool that can help train students to put together arguments, so dim the lights for presentation time. Presentation projects blend left and right brain activity, combining scientific, logical, analytic thinking with creativity and communication skillz. Groups of students can prepare and present talks that focus on developing and defending arguments about the three sources of inheritable genetic variation.

Disciplinary Core Ideas

LS3.B – Variation of Traits: In sexual reproduction, chromosomes can sometimes swap sections during the process of meiosis (cell division), thereby creating new genetic combinations and thus more genetic variation. Although DNA replication is tightly regulated and remarkably accurate, errors do occur and result in mutations, which are also a source of genetic variation. Environmental factors can also cause mutations in genes, and viable mutations are inherited.

In order to satisfy this performance expectation, students should already be comfy with the basics of the genome and how it determines our traits. They should understand genotype, phenotype, mitosis, differential gene expression, and sexual reproduction. Remember, meiosis should be covered, but students don't need to memorize its specific stages or mechanisms.

Once they have those ideas down, here are the core ideas for this performance expectation. Besides crossovers during meiosis, mutations can come from errors in DNA replication during mitosis, and from the environment. UV rays from tanning booths (and the sun), cigarette smoke, viruses, chemicals, ionizing (nuclear) radiation, and babies crying can all cause mutations in DNA that sometimes change cells' phenotypes. Not all mutations are heritable, though.

In order for non-meiotic mutations to persist over generations and influence population traits, the mutations must happen in gametes and cannot result in early death (i.e., influence viability). Mutations in other types of cells can affect an individual's phenotype but aren't passed down to the next generation.

One way to spice up this DCI is by talking with students about genetic science and GMOs as examples of inheritable mutations caused by the environment (us, in fact).

LS3.B – Variation of Traits: Environmental factors also affect expression of traits, and hence affect the probability of occurrences of traits in a population. Thus the variation and distribution of traits observed depends on both genetic and environmental factors.

Put simply, this disciplinary core idea addresses "nature versus nurture." There's long been a debate surrounding whether some traits are based purely on genetics or just on the way someone was raised. Debate no longer; the expression of every trait is influenced by both genetics and environment, but the extent of this influence varies.

Risk isn't just a really complicated board game about world domination; it's also a term used to describe exposure to factors in our environment that increase or decrease the likelihood of expressing phenotypes foretold by our genotype. If you have the genes predisposing you to heart disease, the more greasy fries you eat, the more likely you are to develop heart disease. Don't worry, though, you can still have your occasional McDonalds fix because if you exercise, your risk of developing heart disease goes down.

Basically, students should understand that whether controlled by choice or not, our environment influences our well being.

Science and Engineering Practices

Engaging in Argument from Evidence: Make and defend a claim based on evidence about the natural world that reflects scientific knowledge, and student-generated evidence.

Students should realize that the way they argue with their mom over cleaning their room is very different from the way they present a scientific argument. The former might play out like this:

Mom: "You're room's a mess! Your clothes are all over the floor, your bed's unmade, and it smells like old gym socks. Clean your room!"

Student: "No, Mom. My room isn't that dirty. It's way cleaner than the last time you asked me to clean my room. I'll just plug in one of those air fresheners and it'll smell like roses. Done!"

That was a subjective argument between two people who disagree on the definition of dirty. A more scientific argument, however, might sound like this:

Mom: "Your room is really dirty. Time to clean up!"

Student: "Hmmm (looks around room). I'm not sure if this qualifies as dirty. Let's see…(looks up the definition of dirty)…a dirty bedroom means the bed's unmade, clothes are on the floor, and it smells like old gym socks. Huh! Well, most of that matches, but I think it smells like roses. Dad?!"

Dad: "Yes?"

Student: "What does it smell like in here?"

Dad: "Smells like old gym socks."

Mom: "That's what I think!"

Student: "Well, I guess we've done a test and the majority says it smells like old gym socks. Even though the sample size is small, I have to admit that my room does match up to the standard definition of being dirty. I guess I'll start cleaning!"

Mom: ~shakes head and walks away~

Using evidence to make and defend arguments and to critique others' arguments is a modern, cross-disciplinary skill used inside and outside the classroom. This skill comes in handy when evaluating information in the media and making informed decisions at the polls.

To master this science and engineering practice, students should be able to use data to create and support their claims, evaluate their own and others' claims to identify and explain strengths and weaknesses, and recognize the major features of scientific arguments (hypotheses/claims, evidence/data, and explanations) in examples. That's the goal behind the activity suggestions we threw out there: to get them gathering evidence, thinking critically, and formulating scientifically groovy claims.

Crosscutting Concepts

Cause and Effect: Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects.

If there was a robbery and our goal was to find the perpetrator, what evidence would you rather have: a) testimony from a neighbor who heard a crash next door at the time of the burglary, b) footage from a security camera showing a figure dressed in black entering the house right before the robbery, or c) fingerprints (not the owner's) on the open vault door? While a) and b) are indirect, correlative evidence that a robbery occurred, only c) provides causal, empirical evidence that a particular person committed the robbery.

Students should understand that solid experiments are carefully designed to parse out data indicating correlation (one thing happens along with another) and causation (one thing leads to another). Even though your students are learning to be biologists, not detectives, nailing down that correlation doesn't equal causation will help students find and generate quality (empirical) data to master this performance expectation.