Why Does a Black Cow Have a Brown Calf? Allele Inheritance, Punnett Squares & Pedigree Analysis
Shared by A STEM Educator
Students will analyze patterns of inheritance using Punnett squares and pedigree charts to explain how dominant, recessive, and co-dominant alleles are passed from parent organisms to offspring, supporting NGSS MS-LS3-2.
Lesson Overview
Students investigate the puzzling phenomenon of unexpected coat colors in cattle herds to build understanding of allele inheritance, Punnett squares, and pedigree analysis — connecting to real-world agricultural selective breeding and genetic counseling.
Materials
- Printed Punnett square worksheets (one per student)
- Printed pedigree analysis handouts (one per student)
- Colored pencils or markers (red and white for co-dominance activity)
- Coin sets (2 per pair — for simulating allele segregation)
- Cattle coat color trait cards (see cardSets)
- Whiteboard or large paper for VNPS group work
- Printed investigation handout (one per student)
- Sticky notes (for misconception parking lot)
Scaffolded Task Progression
Using the Cattle Trait Cards, sort the offspring coat color cards under the correct parent pair heading on your desk. Then answer: Which parent coat colors surprised you most when you saw their offspring? Write one sentence explaining what you think is happening.
*Agricultural context:* A rancher keeps records of every calf born. Why might it matter to predict what coat color a calf will have before it is born?
In Angus cattle, black coat () is dominant over brown coat (). A rancher crosses two black cattle that are both carriers of the brown allele.
1. Write the genotype of each parent.
2. Complete the Punnett square below.
3. List all possible offspring genotypes and their probabilities.
4. What fraction of offspring are predicted to be brown? What fraction are black?
[ Interactive graph / diagram — available in the full lesson ]
*Genetic counseling connection:* If this were a human trait (like a recessive genetic condition), what would a genetic counselor tell two carrier parents about their chances of having an affected child?
Unlock the full lesson
See all 4 scaffolded tasks, the full answer key, warm-up, exit slip, and a print-ready version — free to start.
Create a free accountAlready have an account? Sign in
Like this lesson but want to tweak it?
Make an editable copy and adjust the tasks, warm-up, and answer key to fit your class — no need to start from scratch.