Surveys of inherited traits (earlobes, tongue rolling), measuring continuous variation, and bead/coin models of Mendelian crosses.
4 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
The syllabus exemplar investigates earlobes in your class and families. Here’s how to run it and analyse it.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
Discontinuous traits (earlobes, tongue rolling); phenotypes of students, siblings, parents; genotypes by Punnett squares.
Bags = parents; draw = fertilisation; tally; expect 1:2:1 genotypes, 3:1 phenotypes.
Measure 30+; class intervals; histogram (bell curve).
Small samples; unreliable family data; polygenic traits.
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Try it in your notebook first, then reveal the solution one step at a time.
Try it in your notebook first, then reveal the solution one step at a time.
| In the model | Represents |
|---|---|
| Each bag | One heterozygous parent |
| Red / white bead | Dominant / recessive allele carried by a gamete |
| Equal numbers of each bead | The parent makes equal numbers of the two types of gamete |
| Drawing one bead from each bag | Random fertilisation |
| Replacing the bead | Each parent makes huge numbers of gametes |
Models are judged on whether every part stands for something real.
Bead model: bag = parent, bead = gamete, two beads = baby.
Genetic counsellors in Caribbean clinics explain inheritance risks — for example of sickle cell disease — using exactly these probabilities: each pregnancy is an independent chance event.
Toss two coins 50 times (heads = R, tails = r) and record RR, Rr and rr. Combine your results with a friend’s. Do the combined results get closer to 1 : 2 : 1?
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
6 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Write full answers, then reveal the mark scheme and tick the points you earned (7 marks in total). Your answers are saved on this device.
Question 1 [7 marks]
Shantelle’s parents both have free earlobes; two of their three children have attached earlobes.
(a) Assign genotypes and show a genetic cross that explains this family. [5]
(b) State TWO limitations of a class earlobe survey. [2]
Everything in this lesson is based on these parts of the CXC syllabus and papers.