Heredity Tidbit Participants: Facilitator:

Virginia Carson Chris TubbsCharlie JansonDevon QuickJohn ReissMelissa Rowland-GoldsmithMark Wilson

Learning goals

Students will understand characteristics of evidence in science Students will confidently choose and defend evidence-based positions Students will understand the relationship between genotype and phenotype

Context

Students have covered concepts of Probability vs. frequencyMutationsGenotypePhenotype

Learning outcomes Students will be able to interpret a graph

relating genotype to phenotype 

Students will be able to recognize and interpret environmental effects on phenotype/genotype relationships

  Students will be able to apply the

concepts of expressivity and penetrance to an example of population variation

 

The phenotype of breast cancer

Background: Normal BRCA is protective gene against breast

cancer (codes for a tumor suppressing protein) Some people have BRCA gene mutation that makes

the protective protein non-functional (tumors not suppressed) Several mutations of this gene identified

Clicker Question:Do genes cause breast

cancer?

A. YesB. No

Look at my Frogs

The frogs in population A are genetically identical and look the same.

GROUP Agenotype A1/A1:

Look, more Frogs

The frogs in B are also genetically identical (to each other)

What might explain why some B frogs have spots and other do not? (shout out)

GROUP Agenotype A1/A1:

GROUP Bgenotype A2/A2:

Oh wait, I have more Frogs

The frogs in C are genetically identical (to each other), but have variable numbers of spots

What is different about the pattern of variation in C compared to B? (talk with your neighbor)

GROUP Agenotype A1/A1:

GROUP Bgenotype A2/A2:

GROUP CGenotype A3/A3:

What caused all the variations?

http://www.herpnet.net/Iowa-Herpetology/index.php?option=com_content&task=view&id=29&Itemid=26

Scientific jargon

Complete penetrance

Incomplete penetrance

Complete penetrance, variable expressivity

GROUP Agenotype A1/A1:

GROUP Bgenotype A2/A2:

GROUP CGenotype A3/A3:

1 – minute paper, then swap

Summary

Genotype is NOT always = Phenotype!

Environmental factors and chance events affect both penetrance and expressivity

Clicker Question:So, now what do you think, does a gene cause breast

cancer?

A. YesB. No

Incidence of breast cancer vs. age of women in US

Incidence of breast cancer vs. age of women in US

Incidence of breast cancer vs. age of women in US

What does this red line tell you? (shout out)

Clicker Question: Using the graph, will everyone with the BRCA

mutation develop breast cancer?

A. YesB. No

Factors associated with Breast Cancer

You could do some research on this and list specific environmental effects, chance and genetics as making someone more susceptible to developing breast cancer, but simply having the gene mutation on BRCA does not mean one will always develop breast cancer.

The severity of breast cancer relates to expressivity. If one breast is affected or two or the ovaries as well – the more cancer, the more expressivity.

Clicker Question:What do you think now?

Does a gene cause breast cancer?

A. YesB. NoC. Sometimes?

Breast Cancer Incidence Q: which of these is

true?A. Most people with

breast cancer have the BRCA1 mutation

B. BRCA1 mutation is 100% penetrant

C. More than 50% of people with BRCA1 mutation will develop breast cancer

Putting it in a Bigger Context:Breast cancer and BRCA1 incidence in US women

After today You should be more familiar with

graphical representation of data 

You should recognize that environment and genotype influence phenotype

You should be able to define and apply the concepts of expressivity and penetrance to an example of population variation

 

Summative assessment: Essay Question

Your sister has just met with a genetic counselor. The genetic counselor told her that she had the mutated form of the BRCA1 gene and provided her the accompanying graph.

1. Explain to your sister why this is not a death sentence.

2. How is this example relevant to the idea that genotype does not equal phenotype? Hint: use the words penetrance and expressivity.

Alternative graph that could be used, includes family history