Breaking (Down) the Law: Mendel’s LawsMay 17, 2013Athens, GAHeredity Group AKA“The Chiasmatics”

Unit Context Introductory level majors biology

2-3 Weeks, OR As long as it takes to achieve the learning objectives

Unit Learning GoalStudents will understand how allelic

segregation and independent assortment result in inheritance of characteristics through the process of meiosis and sexual reproduction.

Unit Outcomes

Define terms(Knowledge) and describe their hierarchical relationships (Comprehension): locus, gene, alleles, DNA, chromosomes, gametes, segregation, independent assortment

Explain the process of segregation and independent assortment and how it relates to crosses. (Comprehension)

Given parental genotype of a cross, predict phenotypic and genotypic frequency for two traits using Punnett square. (Application)

Unit Outcomes• Given a phenotypic ratio, infer parental

genotypes (Analysis)• Create a diagram that demonstrates the

segregation of alleles at two independently-assorting genes during gamete formation. (Synthesis)

• Diagram how the process of meiosis gives rise to gametes for two independently-assorting traits. (Synthesis)

• Given a set of data, determine if the data provided fit a particular type of inheritance. Provide a possible explanation to support your inference (Evaluation).

Tidbit Rationale:Why did we choose this particular learning objective?

Relative importance of this topic as a foundation for future concepts (scaffolding)

Difficult concept for students to learn (high abstraction and cognitive load)

Many misconceptions about this topic and its connection to meiosis

Prior Knowledge:

Students will…Understand DNA as genetic

material (allele, chromosome) Understand meiosis and sexual

reproductionUnderstand and complete

monohybrid crosses.

X

AA aa

?What is the genotype of the offspring?

A) AaB) aaC) AAD) BB

Tidbit Step 1

Open envelope #1, which contains 8 pieces of paper each of which represents an allele (A, a, B, b).

Use these pieces of paper to create all the possible gametes produced by a heterozygous parent through independent assortment.

Review Question Looking at your cards, what does

each letter represent?

A. ChromosomeB. AlleleC. GeneD. Gamete

Review Question Looking at your cards, what do the

upper versus lower case letters represent?

A. Dominant vs. Recessive AllelesB. Dominant vs. Recessive GenesC. Genotype vs. PhenotypeD. Homozygous vs. HeterozygousE. Male vs. Female Gamete

Review QuestionWhat cell division process creates

the haploid cells that become or produce gametes?

A) MitosisB) MeiosisC) Fission D) Budding

Clicker Question

Which of the following is the correct set of possible gametes for your cards?

A. AA, Aa, BB, BbB. A, B, a, bC. AB, ab, AB, abD. aa, bb, BB, AAE. AB, Ab, aB, ab

Tidbit Step 2

We need 8 student volunteers.

Please grab one sign from the table.

You are a chromosome from a diploid organism with two chromosome pairs (see diagram above).

Tidbit Step 3Organize yourselves into gametes.

Prompt questions Are gametes haploid or diploid? Do gametes have two copies of the same

gene? Is this all the possible combinations?

Tidbit Step 4Line up students horizontally at

front of class

Tidbit Step 5 Now open the second envelope ,

which contains 8 more pieces of paper each of which represents an allele (A, a, B, b).

Use these pieces of paper to create all the possible gametes from the heterozygous male parent.

Tidbit Step 6We now need 8 more volunteers.

Please grab a card and organize yourselves into gametes.

Line up at a right angle to original group (e.g. on left aisle of the classroom).

Clicker QuestionNotice that each of the two groups

have slightly different color shades (bright and pale). What do the two shades represent?

A) Different allelesB) Different genesC) Different chromosomesD) Different sexes

Tidbit Step 7What have we just created?Now sit down and check your cards

and rearrange them so that they match what we have created.

AA Aa aA aa

BB

Bb

bB

bb

AB Ab aB ab

AB

Ab

aB

ab

AA AA BB BB

aa

aa

bb

bb

AA AA aa aa

BB

BB

bb

bb

A

C

B

D

Which Punnett square represents a cross between two heterozygous parents?

Clicker Question

What does each two-letter combination (e.g., AB) represent, assuming independent assortment?

A) Alleles from 2 genes on 1 chromosomeB) Alleles from 2 genes on 2 different

chromosomesC) 2 alleles from 1 geneD) The same allele from different sexes

On paper, identify the different parts of the Punnett square numbered below.

AB Ab aB Ab

AB

Ab

aB

Ab

1

2

3

Summative Assessment Questions:

1. Reflection: Summarize the activity that we completed in class today using the following terms: alleles, independent assortment, meiosis, gamete, and random segregation.

2. Assume a simple dominant inheritance pattern in peas with Y = green, y = yellow, R = round, and r = wrinkled. Find the genotypic and phenotypic ratio from the following two crosses

a. RrYy x RrYyb. RrYy x rryy

Possible Extensions1. Use this human demonstration technique to

model meiosis and gamete formation.

2. Extend the human Punnett square here to show a male and female gamete joining to produce an offspring. (Or even using lots of volunteers to show all possible offspring combinations in the Punnett square – this would require 64 additional volunteers and appropriate space to create the entire Punnett square.)

3. Let the letters represent alleles for real world traits to make the process more tangible.

References I Mbajiorgu. (2007). Science Education, 91(3),

419-438. Kibuka-Sebitosi. (2007). J. o. Biological

Education, 41(2), 56-61. Brown. (1990). J. o. Biological Education,

24(3), 182-186. Smith. (1991). J. o. College Science Teaching,

21(1), 28-33. Oztap, Ozay, & Oztap (2003). J. o. Biological

Education, 38(1), 13-15.

References II Dikmenli. (2011). Scientific Research &

Essay, 5(2), 235-247. Ozcan, Yildirim, & Ozgur. (2012). Procedia –

Social & Behavioral Research, 46, 3677-3680

Karagoz & Cakir. (2011). Educational Sciences: Theory & Practice, 11(3), 1668-1674.

Sesli & Kara. (2012). J. o. Biological Education, 46(4), 214-225.