Science 7–10 · Year 10

Variation in the class: continuous measurements and the myth of single-gene traits

Science understanding: Biological sciences (AC9S10U01 is cited for the Mendelian model the class data are tested against, not for the concept: ACARA v9 has no Year 7 to 10 content description on continuous or polygenic variation, while the NSW Stage 5 Genetics and evolutionary change content point that multiple genes and multiple environmental factors interact in the development of most traits carries the concept directly, under SC5-GEV-02)

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Most human traits vary continuously and depend on many genes and the environment, so class data for tongue rolling or earlobe shape do not fit a single dominant and recessive allele.

What you need

30 cm rulers for hand span
A class tally sheet for categorical traits: tongue rolling, earlobe attached or free, hitchhiker's thumb (the University of Delaware myths pages review the family evidence for each)
Graph paper or a spreadsheet

How to do it

Measure each learner's hand span (thumb tip to little finger tip, hand spread) to the nearest millimetre and record it anonymously.
Draw a histogram of hand span in 10 mm bins; calculate the class mean and standard deviation.
Count how many spans fall within one standard deviation of the mean and compare with the 68 % expected for a bell-shaped distribution.
Tally the categorical traits. For each, look up the University of Delaware summary of family studies and record whether parents who both lack the trait have children who show it.
Decide, trait by trait, whether the class data and the family evidence are consistent with one gene and two alleles.

What you should see

Hand span gives a roughly bell-shaped histogram; in a class of 30 about 20 (68 %) fall within one standard deviation of the mean and about 29 (95 %) within two. For tongue rolling the University of Delaware review reports family studies in which two non-rolling parents have children who can roll, which a simple recessive model does not allow, and identical twins who differ in the trait; for earlobes and hitchhiker's thumb it reports continuous variation rather than two classes, so the family data do not fit one gene with two alleles. The learner knows the analysis worked when the histogram has a single peak near the mean and when each categorical trait carries a written verdict backed by the cited evidence.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Tongue rolling, earlobe attachment and eye colour are each controlled by one gene.
Dominant means common.
A trait that runs in families must be genetic; shared environment also runs in families.

Safety card

Low riskLearners carry it out

Hazards

No hazard is listed.

Controls

Data recorded without names; any learner may decline any measurement

Note

No hazards. Personal data stays in the room and is not published.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7–10 Syllabus (2023)SC5-GEV-02 SC5-WS-05 SC5-WS-06
Australian Curriculum v9AC9S10U01AC9S10I04AC9S10I05AC9S10I06

Sources

The pages the author read to write this activity.

All Concept Studio activities