Mendel’s Mighty Missing Meiotic Mechanism

With special thanks toKathrin Stanger-Hall

andJess Blum

University of North Carolina, Chapel HillJean DeSaixKelly Hogan

University of California, Santa BarbraRolf Christoffersen

Stu Feinstein

Kansas State UniversityEva Horne

Robbie Bear

Teachable Unit: Heredity

Topic: Connecting Meiosis with Mendelian Inheritance

Context: Large Introductory Biology Course.

Assumed Basic Knowledge:

• Chromosome segregation into gametes during meiosis

• Mendelian inheritance

Learning Goal :

How meiosis relates to the inheritance of alleles of two traits.

Learning Outcome for Teachable Tidbit:

Predict how the arrangement of chromosomes in meiosis I will determine the allele combinations in a Punnett Square.

Tidbits

AaBb aabb

A = activea = passiveB = bigb = little

Active & Big passive & little

ab

AB

Gonad

Single cell

Tidbit

Each person = chromosomeColor indicates parental origin

- pink = maternal origin- blue = paternal origin

Letter = allele

a

bA

B

What is the relationship between the chromosome carrying the “A” allele and the chromosome carrying the “a”allele?

Check your vocabulary…

Homologs

Is a Tidbit gonad cell a diploid or a haploid cell and how do you know?

Diploid vs. Haploid

- same genes, can be different alleles

Two sets of all chromsomes. Example: AABB

One set of all chromosomes. Example: AB

You are all the directors of this show!

What needs to happen before we start our production of meiosis?

Check your vocabulary…

What is the relationship between the chromatid carrying the “a” allele and the other chromatid attached to it carrying the “a”allele?

Sister chromatids

Homologs - same genes, can be different alleles

- same genes, identical alleles

At metaphase I, how should the alleles be arranged on the metaphase plate?

A)

D)

B)

C)

A A

a a

B B

b b

B B

b bA A

a a

A A a a

B B b b

b b B B

A A a a

At metaphase II, how should the alleles be arranged on the metaphase plate?

A)

D)

B)

C)

b b B BA A a a

A AB Ba ab b

A A

B B

a a

b b

b b

A A

B B

a a

When the actors did this, why did we only get half of the expected

types of gametes?

Gonad

A A a a

B B b b

b b B B

A A a a

b b B B

A A a a

A A a a

B B b b

How can we get all of the possible gamete types?

D)

B) A A a a

B B b b

b b B B

A A a a

Homework:Draw the two cells that would result from meiosis I for options B and D.

Then draw the outcome of meiosis II for both options