Meiosis and Biological Sex Teaching Box
Let’s talk about sex—the biological concept and the processes that determine it. This one-week instructional sequence reviews meiosis and introduces biological sex, including how sex is determined and expressed in humans on the cellular and whole-organism levels. This classroom-tested, NGSS-aligned resource makes a great supplemental unit or precursor to a genetics unit.
Grade Level & Course
High school biology
Author & Affiliation
Biology teacher, Mountain View High School
Resource 1: Meiosis Models
Help students create a preliminary model of meiosis (model 1) and a second, more complete and accurate model of meiosis.
On the Model 1 paper, ask students to draw what they think meiosis looks like. It’s probably best not to use the word "meiosis," but rather to ask students to predict how a sperm or egg cell is formed. For additional engagement, you can talk about the interesting reproductive strategy of the spider mite (Arrhenotoky, a type of parthenogenesis).
After students learn about meiosis through a mode of your choice (video, textbook, etc.), have them make a second model on the Model 2 paper. The paper has two parts (top and bottom) to emphasize independent assortment and recombination. After making Model 2, students should compare Models 1 and 2, reflecting on which parts of their original models were correct and incorrect (and discussing any limitations of their current models).
Be sure to discuss (and perhaps model in a second copy of Model 2) that meiosis can sometimes go wrong. In fact, “chromosome anomalies are extraordinarily common in human gametes, with approximately 21% of oocytes and 9% of spermatozoa abnormal.” (https://www.ncbi.nlm.nih.gov/pubmed/18413061) This is important for two reasons: (1) miscarriages are common and can be a source of stigma, so it’s important to understand how common atypical gametes are, and (2) this is a link to the next topic: DSD, or intersex conditions.
Resource 2: Half-Rooster/Half-Hen Helps Unlock Sex Mystery
Teach students about intersex conditions in a non-human species through an NPR story (audio + transcript) about a chicken whose right side is male and left side female.
Online radio story
This article could be used at any point in the unit, including as homework or enrichment. Since it’s a nonhuman example of an intersex condition, it helps illustrate to students that humans are not the only species in which sex is non-binary.
Resource 3: What It’s Like to be Intersex
In this video made for a popular audience, four individuals describe their experiences with being intersex (DSD).
This video is useful for engaging students before they read the article “Sex Redefined.” For extra effect, you could pause the video after one participant says, “Raise your hand if you have testes…” You can tell students to guess in their heads, and then continue playing the video (most students are surprised by who raises their hands).
It’s important that students realize the limitations of a video like this. Depending on the maturity of the students, you could give a short introduction to the video or have them discuss its limitations. Some things to remember are that (1) this video is produced by Buzzfeed, a company that’s not scientific and whose primary purpose is entertainment/making money, and (2) four intersex individuals do not represent all intersex individuals in the world and can only speak to their opinions and experiences.
Resource 4: Sex Redefined
Explore this article summarizing the research on sex (“What are all the ways to be not fully male/female?”).
I use the edited version and put it on ActivelyLearn.com, a paid website that allows students to read and answer questions using scaffolds like translators and “hear it!” functions.
Before students read, you might have them fill out the first column of this chart to get an idea of what they think and what they know about biological sex. As they read, or after, they can take notes in the second column of the chart. In addition, if you may want to pre-assess whether students know the difference between gender and sex (and perhaps sexual orientation). Some schools use the genderbread person to get these points across. It’s important that students know that they’ll be discussing biological sex rather than gender.
As students read, they should keep track of questions they want to discuss with their classmates. You can collect these questions by using pieces of paper (anonymously), a Google form, or any other way that’s easy for you. Here are examples of questions my students have asked. I strongly suggest that students have a discussion about some of the questions they had. I suggest at least 20 minutes for the discussion. I use groups of four to eight students, but you should structure the discussion according to your knowledge of your class. One way to organize the discussion is:
Round 1: Students select and read quotations that were powerful for them (one per student).
Round 2: Students select and read quotations that were confusing for them (one per student).
Round 3: Students ask each other (or you ask students) to elaborate on why they found the quotations powerful/confusing.
Round 4: If there’s time, students can use the list of questions to discuss whatever they find interesting.
Round 5: Students say words/sentences (one per student) to summarize anything they learned or anything they feel (“confused” or “not everyone is male or female” might be possible responses from students).
Science and Engineering Practices
Asking Questions and Defining Problems
Ask questions that arise from examining models or a theory to clarify relationships. (HS-LS3-1)
Constructing Explanations and Designing Solutions
Construct an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. (HS-LS1-1)
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. (HS-LS-2)
Disciplinary Core Ideas
LS1.A Structure and Function
All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins. (secondary to HS-LS3-1) (Note: This Disciplinary Core Idea is also addressed by HS-LS1-1)
LS3.A Inheritance of Traits
Each chromosome consists of a single very long DNA molecule, and each gene on the chromosome is a particular segment of DNA. The instructions for forming species’ characteristics are carried in DNA. All cells in an organism have the same genetic content, but the genes used (expressed) by the cell may be regulated in different ways. Not all DNA codes for a protein; some segments of DNA are involved in regulatory or structural functions, and some have no as-yet known function. (HS-LS3-1)
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. (HS-LS3-2)
Cause and Effect
Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects. (HS-LS3-1)
Science is a Human Endeavor
Science and engineering are influenced by society and society is influenced by science and engineering. (HS-LS3-3)
Cells aren’t just the basis of life; they’re the basis of biology learning.
What is life, and how is life maintained?
This Digital Teaching Box contains resources for teaching introductory genetics.