Download Genetic Basis of Continuous Traits

Group 7. Heritability
“The Nads”
Jane Caldwell
Jonathan Cumming
Michelle Momany
Rob Reenan
Katrina Stewart
Kathrin Stanger-Hall
Kathy Takayama
The Teachable Unit:
Genetic Basis of Continuous Traits
Learning Goals and Intended Outcomes:
• Compare and contrast patterns of inheritance for
traits exhibiting dominant-recessive and incomplete
dominance behaviors.
• Given a frequency distribution of traits in a
population, predict the genotypes, and vice versa.
• Explain the genetic basis for the normal distribution of
a trait in a population.
The Scaffold:
In Previous Lectures…
Previous Lecture:
• Students will have
mastered the basics of
genes
– Chromosomes, DNA
– Gene replication
• Students will have been
exposed to the
concepts of heredity
– Simple Mendelian
inheritance
– Dominant-recessive
behavior
Previous Homework:
• Develop an analogy or
representation to
explain simple
inheritance. Include the
terms below:
– Gene, dominant &
recessive alleles,
genotype, phenotype
• Groups shared this with
another group at the
beginning of the current
lecture for engagement.
Revisit: Mendel’s Peas
• Certain traits exhibited
specific patterns
described by
dominant/recessive
behavior
– Two phenotypes
– Set population ratios
• Such behavior is also
evident in humans
Simple Mendelian Traits
Exercise - “Pair-Ear-Share”
• Based on the
distribution of traits in a
population, scientists
can make inferences
about the genetics of
inheritance in humans
• Pair-Ear-Share
• My ear lobe is:
– A-Detached
– B-Attached
Detached
Attached
Clicker data collection
Single Gene Incomplete Dominance
• Systems often exhibit
discrete yet complex
phenotypic patterns
– Four O’Clocks
– Flowers have simple
patterns of inheritance
• No clear dominance
• Incomplete dominance
http://library.thinkquest.org/20465/genes.html
Population Variation Continuous Traits
• Phenotype frequency patterns often do
not match those we have investigated,
e.g., pea seed shape, earlobe
attachment
– Continuous variation in trait - cholesterol
– Normal distribution in frequency
Class Survey of a Continuous Trait:
How Tall Are You?
•
•
•
•
•
A
B
C
D
E
5’ or shorter
5’1” – 5’4”
5’5” – 5’8”
5’9” – 6’
6’1” or taller
Clicker data collection
Hypotheses for Continuous Variation
Group Discussion and Hypothesis Development
• Group discussion - 2 minutes
• Generate a hypothesis to explain this
height distribution
Hypotheses for Normal Trait Variation
• Incomplete dominance
• Multiple genes
• Environment
The Mating Game:
Multiple Gene-Incomplete Dominance Activity
• Using coins and a cup, we will generate
distributions of “coinotypes” that will be analogous
to genotypes in a population
• The penny is one gene
– Alleles P (heads) and p (tails)
• The nickel is another gene
– Alleles N (heads) and n (tails)
• These two “genes” control the same trait
• Tossing a penny and a nickel together will generate
the genotype of your gamete
• Score your tosses with your “mate”
The Mating Game:
Multiple Gene Incomplete Dominance Activity
• Roll twice, each “parent” record one offspring
genotype
• Scoring the genotypes of your offspring:
A = 0 heads
B = 1 head
C = 2 heads
D = 3 heads
E = 4 heads
Clicker data collection
Mating Game:
Debrief and Assumptions
• Does the curve
approach normality?
• How many
categories?
• If you had another
contributing gene,
how would the
categories change?
• What constraints
has the analogous
system of coins
placed on our
genotypes?
Traits and Distributions
– Discrete phenotypes
– Discrete distributions
• Single gene, incomplete
dominance
– Discrete phenotypes
– Discrete distributions
Trait
Frequency
• Single gene, dominance
Frequency
Summary
• Multiple genes, incomplete
dominance
– Continuous phenotypic traits
– Continuous (normal) distributions
Frequency
Trait
Trait
Why Should We Care?
• Most human traits are multigenic
• For diseases, treatments are not simple
– Multiple genes
– Multiple targets for treatment
• For next week, organize your group and
identify a human disease that involves
multiple genes
– Google: polygenic disease
– Select one and develop a 2 minute presentation
for another class group
Unit: Genetic Basis of Continuous Traits
Basic concepts
of heredity
Scaffold (previous activities):
• Active learning assignment
• Lectures
Review of background:
Active learning exercise:
“Pair-Ear-Share”
Single gene incomplete
dominance example
Representation
of traits in a
population
&
Genetic basis of
normal
distribution
Continuous traits:
• Active learning exercise: Height
• Students generate hypothesis
Mating game:
• Active learning exercise: Coins
• Generation of data
• Analysis of data
• Extension to more complex situations
transition
Thanks to Lianna &
the Summer Institute
GO-NADS!!