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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