Lecture 5 - Chapter 5
Page 1: Weird Genetics
Introduces the wizard gene as recessive and the muggle gene as dominant.
Representation:
Wizard Gene: WW (Recessive)
Muggle Gene: M.M (Dominant)
Relationship: W (wizard) + M (muggle) = M (muggle).
Question of whether to inform the character if it’s just a story.
Page 2: Weekly Plan
Today: Lecture on Chapter 5
Friday: Homework assigned for Chapter 5 & posting of Discussion questions for week 4
Sunday: Evaluate an article from Week 3 activities on Wikipedia
Monday: Adaptive quiz for Chapter 6 and Lecture for Chapter 6
Tuesday: Discussion week 4
Wednesday: Genetics in research/Brenner paper
Friday: Homework due for Chapter 6
Monday: Exam 1 scheduled
Page 3: Review of Monday Calculations
Key genetic concepts to review:
Complete dominance
Incomplete dominance
Codominance
Lethality
Multiple alleles
Penetrance
Expressivity
Conditional alleles
Polygenic traits
Multifactorial traits
Phenocopy
Pleiotropy
Page 4: Genetic Interactions
Learning Goals:
Describe types of genetic interactions (e.g., epistasis)
Predict genetic interactions based on phenotypic outcomes
Explain the molecular basis for genetic interactions
Predict structures of genetic pathways from epistasis analysis
Page 5: Mendel's Dihybrid Crosses
Main Question: Do alleles for different traits separate independently?
Methodology:
P Generation: Round, yellow seeds vs. wrinkled, green seeds
F₂ generation observed
Gametes formation leads to:
Round, yellow: RR YY, RR Yy, Rr YY, Rr Yy
Wrinkled, green: rryy
Phenotypic ratio: 9 Round, Yellow : 3 Round, Green : 3 Wrinkled, Yellow : 1 Wrinkled, Green
Conclusion: Alleles for seed color separate independently of seed shape, resulting in the 9:3:3:1 ratio.
Page 6: Applying Probability and Branch Diagram
The dihybrid cross is broken down into two monohybrid crosses to calculate probabilities:
Expected proportions of each trait:
Shape: 3/4 Round
Color: 3/4 Yellow
Combining probabilities with branch diagram gives:
Round, yellow: 9/16
Round, green: 3/16
Wrinkled, yellow: 3/16
Wrinkled, green: 1/16
Page 7: Phenotypic Ratios in Dihybrid Crosses
If genes do not interact:
Genotype: A_B_ → Phenotype A and B (9/16)
Genotype: A_bb → Phenotype A (3/16)
Genotype: aaB_ → Phenotype B (3/16)
Genotype: aabb → Phenotype a and b (1/16)
Page 8: Novel Phenotypes in Crosses
Cross between different phenotypes:
Peach X Orange
F₂ generation outcomes: Red, Peach, Orange, Cream.
Conclusion: Ratios predicted from dominances are 9 Red: 3 Peach: 3 Orange : 1 Cream.
Page 9: Interaction of Genes
Genes interact creating novel phenotypes.
Y+Y+ cc yy C+C+ = Red
Y+ _ cc = Peach
yy C+ _ = Orange
yy cc = Cream
Page 10: Phenotypic Ratios with Gene Interactions
With Genetic Interactions:
A_B_ = (9/16) A and B
A_bb = (3/16) A
aaB_ = (3/16) B
aabb = (1/16)
Without Interactions:
Ratio: 9:3:3:1
With Interactions: 12:3:1
Page 11: Clue for Genetic Interactions
Looking for 9:3:3:1 ratio when mating heterozygotes indicates genetic interactions and novel phenotypes in dihybrid crosses.
Page 12: Challenge Problem
Testcross with red pepper that is double heterozygous.
Determine outcomes for different genotypes.
Page 13: Duplicate Interaction Example
A and B together create a novel phenotype.
A_bb = blue
aaB_ = blue
AABB = purple
aabb = white
Page 14: Phenotypic Ratios of Duplicate Interaction
Ratios:
A_B_ (9/16): A and B
A_bb (3/16): A
aaB_ (3/16): B
aabb (1/16): a and b
Interaction Ratio: 9:6:1
Page 15: Epistasis Intro
Definition: One gene’s phenotype can mask that of another gene (epistasis).
Indicates a relationship between the two genes.
Page 16: Recessive Epistasis Example
Example with hair color gene:
B = black (dominant)
b = brown
H = hair (dominant)
h = bald
Phenotypes:
B_H_ = Black hair
bbhh = Bald
Bald gene is epistatic, masking hair color gene.
Page 17: Phenotypic Ratios of Recessive Epistasis
Genotyping ratios for interaction:
A_B_ (9/16) = A and B
A_bb (3/16) = A
aaB_ (3/16) = B
aabb (1/16) = a and b
Resulting Ratio: 9:4:3
Page 18: Dominant Epistasis Example
Hair color genetics:
B = black, b = brown
E = bald, e = hair
Phenotype Examples:
B_E_ = Bald
B_ee = Bald
Dominant allele masks expression of another gene.
Page 19: Phenotypic Ratios of Dominant Epistasis
Genotypes and Resulting Phenotypes:
A_B_ (9/16) = A and B
A_bb (3/16) = A
aabb (1/16) = a and b
Interaction Ratio: 12:3:1
Page 20: Duplicate Recessive Epistasis Phenotypes
Ratios:
9/16 A_B_
3/16 A_bb
3/16 aaB_
1/16 aabb
Interaction Ratio: 9:7
Page 21: Dominant and Recessive Epistasis
Ratios:
A_B_ (9/16)
A_bb (3/16)
aaB_ (3/16)
aabb (1/16)
Interaction Ratio: 13:3
Page 22: Modified Dihybrid Phenotypic Ratios
Different genetic interactions result in:
9:3:1 (no interaction)
9:3:4 (recessive epistasis)
12:3:1 (dominant epistasis)
9:7 (duplicate recessive epistasis)
9:6:1 (duplicate interaction)
15:1 (duplicate dominant epistasis)
Page 23: Summary of Gene Interactions
Explains how two different genes interact, leading to complex ratios distinct from single allele interactions.
Epistasis is critical in mapping pathways within genetics.
Page 24: Gene Interaction with Novel Phenotypes
Crosses indicated novel phenotypes leading to:
F₂ generation ratios: 9 Red, 3 Peach, 3 Orange, 1 Cream.
Page 25: Color Molecules and Interactions
Description of carotenoid-producing color interactions:
Y gene product: alters color
C gene product: modifies color further
Both genes can influence combined expression.
Page 26: Recessive Epistasis in Dogs
Example with coat color in dogs:
B = black, b = brown
E = pigment deposition
Results in yellow lab phenotype (ee).
Page 27: Duplicate Recessive Epistasis Example
Work with enzyme function:
A = Enzyme I, a = non-functional Enzyme I
B = Enzyme II, b = non-functional Enzyme II
Results: 9:7 ratio
Page 28: Duplicate Dominant Epistasis
Understanding gene dominance:
A and B can independently produce a phenotypic effect
Genotypes yield 15:1 interaction with one dominant allele masking expression.
Page 29: Dominant Epistasis Example Overview
Interaction leading to dominant epistasis depicted with possible phenotypes:
Function of Enzyme I and II demonstrated via dominance.
Page 30: Dominant and Recessive Epistasis Summary
Complex interactions:
Dominant alleles can mask the expression of the other
Resulting interactions include intricate expression patterns.
Page 31: Sample Problem Practice
Cross a poppy with lacerate leaves versus normal leaves to determine genetic outcomes in F2 generation (249:16 ratio).
Page 32: Significance of Gene Interactions
Importance of understanding genetic pathways in biology.
Implications in research for drug targets and understanding life functions.
Page 33: Biological Pathways Overview
Visual representation of various signaling pathways involving genes, proteins, and interactions affecting cellular processes and functions.
Page 34: Basic Genetic Pathways
Simple models of gene interactions:
Activation and inhibition dynamics illustrated through various scenarios.
Page 35-39: C. elegans Mutant Studies
Research on daf-2 gene affecting lifespan through its relationship with daf-16 gene, showing the impact of mutations on life expectancy.
Investigation of phenotypes in different genetic contexts:**
Double mutant interactions suggest relationships between these genes regarding aging pathways.