Lecture 7: Hardy-Weinberg principle

Question 1

Evolution is driven by what 4 processes: NGGM

Answer 1

1. Natural selection
2. Genetic drift
3. Gene flow
4. Mutation

Question 2

DEF: increases the frequency of alleles
that contribute to reproductive success in a particular environment

Answer 2

Natural selection

Question 3

DEF: causes allele frequencies to change
randomly

Answer 3

Genetic drift

Question 4

DEF: occurs when individuals leave one
population, join another, and breed

Answer 4

Gene flow

Question 5

DEF: modifies allele frequencies by continually
introducing new alleles

Answer 5

Mutation

Question 6

The Modern Synthesis refers to the era in the
early 1900s. What is one product of this era? (a model)

Answer 6

The Hardy–Weinberg principle

Question 7

Hardy–Weinberg principle is the mathematical ___ _______ for study of evolutionary processes

Answer 7

Null hypothesis

Question 8

In 1908, G. H. Hardy and Wilhelm Weinberg
– Wanted to know what happened in an entire
____ when all individuals—and thus all possible
genotypes—bred
– Like Darwin, engaged in _______ ________

Answer 8

Population, population thinking

Question 9

Hardy and Weinberg imagined that all of the
alleles from all gametes in each generation go into
a single group
– called a ____ _____ and then combine randomly

Answer 9

Gene pool

Question 10

They calculated what would happen if
– pairs of _____ picked randomly, many times, and
each pair combined to produce _____

Answer 10

Gametes, offspring

Question 11

The calculations predict the _____ of the
offspring that the population would produce,
– as well as the ______ of each genotype

Answer 11

Genotype, Frequency

Question 12

Deriving the Hardy–Weinberg Principle:
- a gene with two alleles, A1 and A2
- The frequency of A1 is represented by p
- the frequency of A2 is represented by q
- Because there are only two alleles, p + q = 1

• three genotypes are possible: A1A1, A1A2, and A2A2
• The frequency of the A1A1 genotype is p^2
  – The frequency of the A2A2 genotype is q^2
  – The frequency of the A1A2 genotype is 2pq

T or F

Answer 12

True

Question 13

What is the Hardy–Weinberg equation2

Answer 13

p^2 + 2pq + q^2 =1

Question 14

When alleles are transmitted via meiosis and
random combination of gametes. The ____ ________DO NOT change

Answer 14

Allele frequencies

((Therefore when allele frequencies are calculated for the next generation, the frequency of A1 is still p and the frequency of A2 is still q)

Question 15

The Hardy–Weinberg model is based on what 5
assumptions about the behaviour of populations
and alleles?

Answer 15

1. No natural selection at the gene in question
2. No genetic drift affecting the gene in question
3. No gene flow
4. No mutation
5. Random mating with respect to the gene in
   question

Question 16

DEF: all members of the parental generation contribute equal numbers of gametes to the gene pool

Answer 16

No natural selection at the gene in question

Question 17

DEF: i.e., random allele frequency
changes) affecting the gene in question—alleles not
picked by chance because assumes population is large

Answer 17

No genetic drift affecting the gene in question

Question 18

DEF: no new alleles are added by immigration
or lost through emigration

Answer 18

No gene flow

Question 19

DEF: no new alleles are introduced to the
gene pool

Answer 19

No mutation

Question 20

DEF: no mate choice; gametes combine
randomly Copyright

Answer 20

Random mating with respect to the gene in
question

Question 21

2 conclusions of the Hardy-Weinberg
principle:

1. The allele frequencies in a population will not
   change, generation after generation
2. If the allele frequencies in a population are given
   by p and q, the genotype frequencies will be
   given by p^2, 2pq, and q^2

T or F

Answer 21

True

Question 22

Hardy–Weinberg Principle Serve as a ____ Hypothesis

Answer 22

Null

Question 23

CASE STUDY 1: Are MN Blood-Type Alleles in
Humans in Hardy–Weinberg Equilibrium

NO ANS

Question 24

What are the 2 alleles that human populations have for the MN blood group?

Answer 24

M and N, which code for protein on surface of red blood cell

Question 25

M and N are _____ (heterozygotes have both M and N versions of protein on red blood cells)

Answer 25

Codominant

Question 26

The genotype of a person can be determined from blood samples - Genotype may be ___, __, or __

Answer 26

MM, MN, or NN

Question 27

Analysis to determine if the population is in Hardy–Weinberg equilibrium based on four steps NO ANS

Question 28

Define Estimate genotype frequencies

Answer 28

by dividing total number of individuals with each genotype by the total number of individuals in the sample

Question 29

Define Calculate observed allele frequencies

Answer 29

from the observed genotype frequencies Ex. Example: The frequency of the M allele = frequency of MM homozygotes + half the frequency of MN heterozygotes.

Question 30

Define calculate the genotypes expected

Answer 30

Use the observed allele frequencies according to the Hardy–Weinberg principle

Question 31

Define compare

Answer 31

Statistically compare the observed and expected values

Question 32

In a population of 2,345 people located in Inuit, Greenland: 1,958 had genotype MM, 366 had genotype MN, and 21 had NN. Calculate: 1. The observed genotype frequencies (MM, MN, NN) in the population 2. The observed allele frequencies of M and N in the population 3. The expected genotype frequencies if the population were in Hardy-Weinberg equilibrium 4. Compare the observed and expected genotype frequencies NO ANS

Question 33

The observed and expected MN genotype frequencies were almost identical. Thus: – For every population examined, the genotypes at the MN locus are in Hardy–Weinberg equilibrium – The MN blood groups were not being affected by any of the four evolutionary processes – Mating was random with respect to this gene – Null hypothesis is accepted NO ANS

Question 34

Natural selection occurs when: - Individuals with certain phenotypes produce more surviving offspring than do individuals with other phenotypes – If certain alleles are associated with these favoured phenotypes, ▪ they increase in frequency while other alleles decrease in frequency – The result is evolution ▪ Hardy–Weinberg model assumption has been VIOLATED T or F

Answer 34

True

Question 35

DEF: the number and relative frequency of alleles that are present in a particular population

Answer 35

Genetic variation

Question 36

Maintaining genetic variation is important – Selection can occur only if heritable variation exists in a population – Lack of variation can make populations less able to respond successfully to changes in the environment, and their average fitness will decline – If environmental change is severe, the population may become extinct T or F

Answer 36

True

Question 37

Natural selection occurs in a wide variety of patterns or modes (4 points)

Answer 37

1. Directional selection 2. Stabilizing selection 3. Disruptive selection 4. Balancing selection

Question 38

DEF: changes the average phenotype in the population in one direction

Answer 38

Directional selection

Question 39

If it continues, the favoured alleles will approach a frequency of __ while disadvantageous alleles will approach a frequency of ___

Answer 39

1.0, 0.0

Question 40

Alleles that reach a frequency of 1.0 are termed ___, and those that reach 0.0 are termed ____

Answer 40

Fixed, lost

Question 41

When disadvantageous alleles decline in frequency, ____ selection is said to occur

Answer 41

Purifying

Question 42

Directional selection in cliff swallows: - A six-day cold spell caused the birds’ primary food, insects, to disappear and many birds died of starvation – Survivors were much larger on average than the birds that died Researchers suggested that the larger birds survived because they had bigger fat stores and did not get as cold as smaller birds. * Larger birds thus were less likely to die from – Exposure to cold – Starvation T or F

Answer 42

True

Question 43

DEF: reduces genetic variation in a trait - Reduces both extremes in a population – No change in the average value of a trait over time

Answer 43

Stabilizing selection

Question 44

Stabilizing selection in human newborns: - Babies of average birth weight survived best – Mortality was high for very small and large babies * Persuasive evidence of stabilizing selection on birth weight in this population – Alleles associated with high or low birth weight were subject to _____ selection – Alleles associated with intermediate birth weight increased in frequency T or F

Answer 44

Purifying, True

Question 45

DEF: - Intermediate phenotypes are selected against and extreme phenotypes are favoured – Has the opposite effect of stabilizing selection – Increases variation in a trait

Answer 45

Disruptive selection

Question 46

Disruptive selection in black-bellied seedcrackers: - Individuals with very short or long beaks survived – Birds with intermediate phenotypes died T or F

Answer 46

True

Question 47

Food (i.e., seed size) is the agent that causes natural selection – Nearby only two seed sizes available: small and large – Small-beaked birds eat small seeds efficiently and large-beaked birds eat large seeds efficiently – Birds with intermediate beaks have trouble with small and large seeds ▪ Alleles associated with medium-sized beaks are subject to purifying selection ▪ Disruptive selection maintains high overall variation in this population T or F

Answer 47

True

Question 48

Disruptive selection can cause _____, the formation of new species

Answer 48

Speciation

Question 49

If individuals with one extreme of a trait mate preferentially with individuals that have the same extreme trait, and individuals with the other extreme values of the trait mate with members of the opposite- sex with the same extreme values – Selection would result in ___ distinct populations, which may eventually form ___ new species

Answer 49

two, two

Question 50

DEF: occurs when no single allele has a distinct advantage - There is a balance among several alleles in terms of their fitness and frequency

Answer 50

Balancing selection

Question 51

1. Heterozygous individuals have higher fitness than homozygous individuals do—called _________ ________

Answer 51

Heterozygote advantage - Consequence is that selection on different alleles is balanced - Genetic variation is maintained in the population

Question 52

2. Certain ____ are favoured at different times or in different places - Although allele frequencies change locally, overall genetic variation in the population is maintained

Answer 52

Alleles

Question 53

3. Certain alleles are favoured when they are rare but not when they are common - _________ ________ selection

Answer 53

Frequency-dependent selection

Question 54

Ex. Rare alleles for colouration in guppies are favoured because predators learn to recognize common colours – Thus, alleles for common colours decrease in frequency and those for rare alleles increase – Over the short term, allele frequencies shift, but variation is maintained over the long term T or F

Answer 54

True