Heredity Tidbit Participants: Facilitator: Virginia Carson Chris Tubbs Charlie Janson Devon Quick John Reiss Melissa Rowland-Goldsmith Mark Wilson
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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
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