Here’s why you’re going to get it wrong on the exam:Teaching by Focusing on Misconceptions

Morris Maduro, Univ of California, Riverside

The Gist

• Intro Biology, 250-500 1st- or 2nd-year students• Chapters 1-16 of Campbell• I give students summary notes, learning

outcomes, past exams, how-to guide[see Poster and BLC Wiki site]

• In class, I cover topics and go straight to the misconceptions (which aren’t in the notes)

Example: “Independent Assortment”

First part: Monohybrid crosses & Mendel’s Law of Segregation

A dihybrid cross

9331

Phenotyperatios:

9 : 3 : 3 : 1

Most of you think that“Independent Assortment”

means“the genes affect different characters.”

This is wrong.

A dihybrid cross

9331

Phenotyperatios:

9 : 3 : 3 : 1

All textbooks depict the 9:3:3:1 ratio using genes exerting ‘parallel’ effects on phenotype.Students misunderstand use of ‘independent’.

Why the misconception?

• Linked genes (which fail to assort independently) are also shown as ‘parallel’ pairs, e.g. b and vg in flies.

• Unlinked genes can act in the same process (e.g. two eye color genes in flies) but still assort independently.

The misconception is falsifiable:

Sample assessment:

In Mendel’s Law of Independent Assortment, the word “assortment” refers to:

(A)The functions of the genes.

(B)Whether genes are on the same chromosome.

(C) Whether single genes show a 1:1 segregation.

(D) Distribution of alleles into gametes.

(E) Whether a cross gives a 9:3:3:1 ratio.

What does this achieve?

• Forces students to re-evaluate what they think they learned previously

• Holds their attention more than just explaining the figures

• They will bring their questions to office hours• Rewards students who attended class

Thank you.

Downloads:BLC Wiki site under Maduro poster abstract (A-11)(sample exams, lecture notes, concepts quiz, FAQ file, etc.)

Sample assessment 2:

A dihybrid AaBb plant is producing gametes. If the two genes assort independently, the four gamete types are ____ in proportion ____:

(A) A, a, B and b; 1:1:1:1

(B) A, a, B and b; 9:3:3:1

(C) AB, Ab, aB and ab; 1:1:1:1

(D) AB, Ab, aB and ab; 9:3:3:1

(E) AB and ab ; 3:1

Sample assessment 3:

Two genes s and t are found on two different chromosomes. The two genes must:

(A)Show less than 50% recombination.

(B)Assort independently.

(C) Affect different aspects of phenotype, like color vs. shape.

(D) Show greater than 50% recombination.

(E) Both (B) and (C) are correct.

Law of Independent Assortment

meiocytein F1, genotype YyRr

OR

TWO POSSIBLE ALIGNMENTS AT METAPHASE I

gametes yR and Yrgametes yr and YR

y

yy

yy