Lecture 4: Hardy-Weinberg Equilibrium Flashcards
Mechanisms of Evolution (Microevolution)
- mechanisms acting WITHIN populations, hence called “population genetics”
- Hardy Weinberg Principle (Mendelian Inheritance)
- Genetic Drift
- Mutation
- Sex: Recombination and Random Mating
- Natural Selection
Mechanisms of Evolution (Microevolution)
- Hardy Weinberg Principle (Mendelian Inheritance)
- Genetic Drift
- Mutation
- Sex: Recombination and Random Mating
- Epigenetic Inheritance
- Natural Selection
act on individuals in a Lamarckian manner
Epigenetic inheritance
Who is considered the “Father of Modern Genetics,” and what contribution did he make to our understanding of inheritance?
- Gregor Mendel
- He presented a mechanism for how traits are passed on, proposing the idea of particulate (genes) inheritance, where individuals pass alleles on to their offspring intact.
Mendel’s Laws of Inheritance
- only one allele passes from each parent on to an offspring
Law of Segregation
Mendel’s Laws of Inheritance
- different pairs of alleles are passed to offspring independently of each other
Law of Independent Assortment
Mendel’s Laws of Inheritance
- Law of Segregation
- Law of Independent Assortment
Using 29,000 pea plants, Mendel discovered the __ ratio of phenotypes, due to __
- 1:3
- dominant vs. recessive alleles
In cross-pollinating plants with either yellow or green peas, Mendel found that the __ always had yellow seeds (dominance). However, the __ consistently had a 3:1 ratio of yellow to green.
- first generation (f1)
- second generation (f2)
Mathematical description of Mendelian inheritance
Hardy-Weinberg Principle
Testing for Hardy-Weinberg equilibrium can be used to assess whether a population is __
evolving
A population that is not evolving shows allele and genotypic frequencies that are in __.
Hardy Weinberg equilibrium
Evolutionary Mechanisms (will put population out of HW Equilibrium):
Genetic Drift
Natural Selection
Mutation
Migration
change expression of alleles but not the frequency of alleles themselves, so they won’t affect the actual inheritance of alleles
*Epigenetic modifications
epigenetic modifications can change __, not __
- phenotype
- genotype
A population in Hardy-Weinberg Equilibrium serves as the __ (for no evolution) to test if evolution is happening.
Null Model
A region of genome sequence (DNA or RNA), that is the unit of inheritance , the product of which contributes to phenotype
gene
Location in a genome (used interchangeably with “gene,” if the location is at a gene… but, locus can be anywhere, so meaning is broader than gene)
locus
Variant forms of a gene (e.g. alleles for different eye colors, BRCA1 breast cancer allele, etc.)
allele
The combination of alleles at a locus (gene)
genotype
The expression of a trait, as a result of the
genotype and regulation of genes (green eyes, brown hair, body size, finger length, cystic fibrosis, etc.)
phenotype
We are diploid (__), so we have _ at a locus (any location in the genome)
- 2 chromosomes
- 2 alleles
If p and q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then for a diploid organism (2 chromosomes)
(p + q)^2 = 1
= p2 + 2pq + q2 = 1
triploid organism
(p + q)^3 = 1
= p3 + 3p2q + 3pq2 + q3 = 1
One locus three alleles
(p + q + r)2 = p2 + q2 + r2 + 2pq +2pr +
2qr
(p + q)c
, where c =
number of chromosomes
Applying the Hardy-Weinberg Principle
* Phenylketonuria (PKU) is a metabolic disorder that results from homozygosity for a recessive allele
* Individuals that are __ for the deleterious __ cannot break down phenylalanine, results in build-up a mental retardation
- homozygous; recessive allele
Rare deleterious recessives often remain in a
population because they are hidden in the
__ (the “carriers”)
heterozygous state
How can you tell whether a population
is out of HW Equilibrium?
- When allele frequencies are changing across
generations - When you cannot predict genotype frequencies from allele frequencies (means there is an excess or deficit of genotypes than what would be expected given the allele frequencies)
used because it is the sum of squared
normal distributions
chi-squared distribution
degrees of freedom
1 = __
2 = __
3 = __
3.841
5.991
7.815
where allele frequencies fluctuate randomly across generations; should perform a Goodness of Fit test to determine whether the frequencies deviate significantly from HW expectations
Genetic drift
Examples of Deviation from Hardy-Weinberg Equilibrium
- Genetic Drift
- Negative selection
- Heterozygote Advantage (or Overdominance)
- Selection favoring either dominant/recessive genotype
AA Aa aa
Generation 1 0.64 0.32 0.04
Generation 2 0.63 0.33 0.04
Generation 3 0.64 0.315 0.045
Generation 4 0.65 0.31 0.04
Genetic Drift
AA Aa aa
0.64 0.36 0
Negative Selection disfavoring aa
AA Aa aa
0.25 0.70 0.05
Heterozygote
Advantage (or Overdominance)
AA Aa aa
0.10 0.10 0.80
Selection favoring aa
