IAL Biology Edexcel – Multiple Alleles, Polygenes

Complete Edexcel IAL Biology lesson (spec 3.21): multiple alleles, ABO blood groups, polygenic inheritance and continuous variation. No prep needed.

Lesson 30 of 32 · Topic 3 · Unit 2 (WBI12) · Spec 3.21 · 60 minutes
The question this lesson answers: what causes continuous variation in a characteristic such as height?

By the end, students can

• Explain multiple alleles using the ABO blood groups, and polygenic inheritance using the addition of gene effects.
• Explain how the environment turns classes into a continuous range, and name five sources of variation.
• Sketch and describe the graph of a continuously varying characteristic.

How the 20-slide lesson runs
A retrieval starter, then two kinds of variation. Multiple alleles (one gene, more than two versions) comes next: ABO blood groups (three alleles, four phenotypes) and “more alleles, more phenotypes: why”. Polygenic inheritance follows: many genes, one characteristic, adding genes from a few classes to a bell shape, and the environment smoothing the steps into a curve. Five sources of variation, sketching the graph, “multiple alleles or polygenic? Read the question”, “words that lose marks” and a “what 3.21 questions ask” slide lead into a quick check. An exit ticket closes the lesson.

Marks students usually lose here

• Treating multiple alleles and polygenic inheritance as the same idea: one gene with several alleles, or several genes each contributing.
• Writing that a person “has three blood group alleles”, when each person inherits only two.
• Sketching a continuous variation graph as bars, or with a skewed or non-symmetrical curve for no reason.

In the folder (13 files)

• PowerPoint, 3-page lesson plan and 18-page student notes with a one-page knowledge organiser
• 8 practice questions (21 marks) and mark scheme, each question on its own page
• 18-mark homework (ABO blood group with codominance, two-gene plant height, seed mass in bean plants, plus spaced retrieval on splicing) with mark scheme
• 5-question misconception check with teacher key
• 5 pages of active-learning printables: Coin-toss polygenes and One gene or many?
• 7 pages of teacher notes (starter and exit mark points, a step-by-step run sheet for every active-learning activity, answer keys), plus catch-up and extension bank decks

Follows Lesson 29 (epigenetics exam practice); Lesson 31 is exam practice on variation. The full 32-lesson Topic 3 bundle is in my shop.

An independent resource by bio_boffin_resources, written by a Biology teacher with 10 years’ experience in a leading international school. Not endorsed by Pearson.