Lecture 4: Hardy-Weinberg Equilibrium

Question 1

Mechanisms of Evolution (Microevolution)

• mechanisms acting WITHIN populations, hence called “population genetics”

Answer 1

• Hardy Weinberg Principle (Mendelian Inheritance)
• Genetic Drift
• Mutation
• Sex: Recombination and Random Mating
• Natural Selection

Question 2

Mechanisms of Evolution (Microevolution)

Answer 2

• Hardy Weinberg Principle (Mendelian Inheritance)
• Genetic Drift
• Mutation
• Sex: Recombination and Random Mating
• Epigenetic Inheritance
• Natural Selection

Question 3

act on individuals in a Lamarckian manner

Answer 3

Epigenetic inheritance

Question 4

Who is considered the “Father of Modern Genetics,” and what contribution did he make to our understanding of inheritance?

Answer 4

• 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.

Question 5

Mendel’s Laws of Inheritance
- only one allele passes from each parent on to an offspring

Answer 5

Law of Segregation

Question 6

Mendel’s Laws of Inheritance
- different pairs of alleles are passed to offspring independently of each other

Answer 6

Law of Independent Assortment

Question 7

Mendel’s Laws of Inheritance

Answer 7

• Law of Segregation
• Law of Independent Assortment

Question 8

Using 29,000 pea plants, Mendel discovered the __ ratio of phenotypes, due to __

Answer 8

• 1:3
• dominant vs. recessive alleles

Question 9

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.

Answer 9

• first generation (f1)
• second generation (f2)

Question 10

Mathematical description of Mendelian inheritance

Answer 10

Hardy-Weinberg Principle

Question 11

Testing for Hardy-Weinberg equilibrium can be used to assess whether a population is __

Answer 11

evolving

Question 12

A population that is not evolving shows allele and genotypic frequencies that are in __.

Answer 12

Hardy Weinberg equilibrium

Question 13

Evolutionary Mechanisms (will put population out of HW Equilibrium):

Answer 13

Genetic Drift
Natural Selection
Mutation
Migration

Question 14

change expression of alleles but not the frequency of alleles themselves, so they won’t affect the actual inheritance of alleles

Answer 14

*Epigenetic modifications

Question 15

epigenetic modifications can change __, not __

Answer 15

• phenotype
• genotype

Question 16

A population in Hardy-Weinberg Equilibrium serves as the __ (for no evolution) to test if evolution is happening.

Answer 16

Null Model

Question 17

A region of genome sequence (DNA or RNA), that is the unit of inheritance , the product of which contributes to phenotype

Answer 17

gene

Question 18

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)

Answer 18

locus

Question 19

Variant forms of a gene (e.g. alleles for different eye colors, BRCA1 breast cancer allele, etc.)

Answer 19

allele

Question 20

The combination of alleles at a locus (gene)

Answer 20

genotype

Question 21

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.)

Answer 21

phenotype

Question 22

We are diploid (__), so we have _ at a locus (any location in the genome)

Answer 22

• 2 chromosomes
• 2 alleles

Question 23

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)

Answer 23

(p + q)^2 = 1
= p2 + 2pq + q2 = 1

Question 24

triploid organism

Answer 24

(p + q)^3 = 1
= p3 + 3p2q + 3pq2 + q3 = 1

Question 25

One locus three alleles

Answer 25

(p + q + r)2 = p2 + q2 + r2 + 2pq +2pr +
2qr

Question 26

(p + q)c
, where c =

Answer 26

number of chromosomes

Question 27

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

Answer 27

• homozygous; recessive allele

Question 28

Rare deleterious recessives often remain in a
population because they are hidden in the
__ (the “carriers”)

Answer 28

heterozygous state

Question 29

How can you tell whether a population
is out of HW Equilibrium?

Answer 29

1. When allele frequencies are changing across
   generations
2. 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)

Question 30

used because it is the sum of squared
normal distributions

Answer 30

chi-squared distribution

Question 31

degrees of freedom
1 = __
2 = __
3 = __

Answer 31

3.841
5.991
7.815

Question 32

where allele frequencies fluctuate randomly across generations; should perform a Goodness of Fit test to determine whether the frequencies deviate significantly from HW expectations

Answer 32

Genetic drift

Question 33

Examples of Deviation from Hardy-Weinberg Equilibrium

Answer 33

• Genetic Drift
• Negative selection
• Heterozygote Advantage (or Overdominance)
• Selection favoring either dominant/recessive genotype

Question 34

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

Answer 34

Genetic Drift

Question 35

AA Aa aa
0.64 0.36 0

Answer 35

Negative Selection disfavoring aa

Question 36

AA Aa aa
0.25 0.70 0.05

Answer 36

Heterozygote
Advantage (or Overdominance)

Question 37

AA Aa aa
0.10 0.10 0.80

Answer 37

Selection favoring aa