Bio U3L1

Question 1

Microevolution

Answer 1

Is a change in allele frequencies in a
population over generations

Question 2

What is bottle neck

Answer 2

refers to a sharp reduction in the size of a population due to environmental events or other factors that significantly decrease genetic diversity.

Question 3

Three mechanisms cause allele frequency change

Answer 3

Natural selection
Genetic drift
Gene flow

Question 4

What causes adaptive evolution?

Answer 4

Natural selection

Question 5

What is a prerequisite for evolution?

Answer 5

Variation in heritable traits

Question 6

How is genetic variation among individuals caused?

Answer 6

differences in genes or other DNA segments

Question 7

What is phenotype the product of?

Answer 7

Inherited genotype and environmental influences

Question 8

How are phenotypic differences determined?

Answer 8

Either by a single gene - classified on an either or basis
Or by two or more genes - vary along a continuum within a population

Question 9

How can genetic variation be measured?

Answer 9

Gene variability or nucleotide variability

Question 10

Average heterozygosity

Answer 10

Measures the average percent of loci that are heterozygous in population

Question 11

How is Nucleotide variability measured

Answer 11

By comparing DNA sequences of pairs of individuals (rarely results in phenotypic variation)

Question 12

Example of phenotypic variation that does not result from genetic differences but from environmental influences

Answer 12

Caterpillars can have different appearances due to chemicals in diet and not their genotype

Question 13

Only genetically determined variation can have

Answer 13

evolutionary consequences

Question 14

population

Answer 14

localized group of individuals
capable of interbreeding and producing fertile offspring

Question 15

gene pool

Answer 15

consists of all the alleles for all loci in a
population

Question 16

A locus is fixed if

Answer 16

all individuals in a population are
homozygous for the same allele

Question 17

How many alleles and what is used to represent their frequencies

Answer 17

2
p and q

Question 18

Frequency of all alleles in a population will add up to

Answer 18

1
p + q = 1

Question 19

Describe The Hardy-Weinberg Principle

Answer 19

If p and q represent relative frequencies of only two possible alleles in a population at a particular locus, then
– p^2 + 2pq + q^2 = 1
– where p^2 and q^2 represent the frequencies of the homozygous genotypes, and 2pq represents frequency of the heterozygous genotype

Question 20

What does the hardy weinberg equilibrium describe

Answer 20

• Describes a hypothetical population that is not evolving
• In real populations, allele and genotype frequencies do change over time
• The 5 conditions are rarely met in nature

Question 21

What are the 5 conditions required for hardy weinberg and what are the consequences if condition does not hold

Answer 21

1. No mutations: Gene pool is modified if mutations occur or if entire genes are deleted or duplicated
2. Random mating: If individuals mate within a subset of the population such as a neighbour or close relatives (inbreeding) random mixing of gametes does not occur and gene frequencies change
3. No natural selection: Allele frequencies change when individuals with different genotypes show consistent differences in their survival or reproduction success
4. Extremely large population size: allele frequencies fluctuate by chance over time (genetic drift)
5. No gene flow: By moving alleles into or out of populations, gene flow can alter allele frequencies

Question 22

Red short-horned cattle are homozygous for the red allele, white cattle are homozygous for the white allele, and roan cattle are heterozygotes. Population A consists
of 36% red, 16% white, and 48% roan cattle. What are the allele frequencies?

Answer 22

Allele counting method since we do not know if this is a weinberg question
Assume 100 individuals = 200 alleles
36% = 36/100 are red and 36x2 is 72 (diploid so multiply by 2)
48/100 are roan ( red + white)
72 + 48 = 120/200 = 0.6
Do the same thing with white
32 + 48 = 80/200 = 0.4

Question 23

q^2 is for dominant or recessive genes?

Answer 23

recessive

Question 24

In a population of 500 people, 6 have a
rare autosomal recessive disorder. How many people are carriers? Assume weinberg assumptions are met.

Answer 24

of carriers = 2pq x 500
q^2 = 6/500
q = √(6/500)
p + q = 1
p = 1- √(6/500)
# of carriers = 2(1-√(6/500)) (√(6/500)) x 500
# of carriers = 97.5

Question 25

Three major factors alter allele frequencies and bring about
most evolutionary change:

Answer 25

Natural selection
Genetic drift
Gene flow

Question 26

Differential success in reproduction results in

Answer 26

certain alleles being passed to the next generation in greater proportions

Question 27

Natural selection can cause adaptive evolution, an improvement in the
Give an example

Answer 27

match between organisms and their
environment
an allele conferring resistance to DDT in fruit flies increased in frequency after DDT was used widely in agriculture

Question 28

Genetic Drift

Answer 28

describes how allele frequencies
fluctuate unpredictably from one generation to the next. The smaller a sample, the greater the chance of
random deviation from a predicted result. Genetic drift tends to reduce genetic variation through
losses of alleles
Reduces variation

Question 29

founder effect

Answer 29

occurs when a few individuals
become isolated from a larger population
Allele frequencies in the small founder population can be different from those in larger parent population
Type of genetic drift

Question 30

bottleneck effect

Answer 30

Type of genetic drift
sudden reduction in population size due to a change in the environment. The resulting gene pool may no longer be reflective of the original population’s gene pool
* If the population remains small, it may be further affected by genetic drift

Question 31

List the effects of genetic drift

Answer 31

1. Genetic drift is significant in small populations
2. Genetic drift can cause allele frequencies to change at random
3. Genetic drift can lead to a loss of genetic variation within populations
4. Genetic drift can cause harmful alleles to become fixed

Question 32

Gene flow

Answer 32

consists of movement of alleles among
populations. Alleles can be transferred through movement of fertile individuals or gametes (for example, pollen)
* Gene flow tends to reduce variation among populations over time
can decrease or increase the fitness of a population

Question 33

Phenylketonuria (PKU) is extremely
common in Ireland, affecting approximately 1 in 4500 live births. Assuming that the population is in Hardy-Weinberg equilibrium, what is the frequency of PKU carriers?

Answer 33

Freq of carriers = 2pq
q = √1/4500
p = 1 - √1/4500
Freq of carriers = 2 x (1-√1/4500)(√1/4500)
= 2.9%

Question 34

Examples of gene flow increasing or decreasing fitness

Answer 34

Increase: Insecticides have been used to target mosquitoes carrying
West Nile virus and malaria. Alleles have evolved in some mosquito populations that confer resistance to these insecticides. The flow of insecticide resistance alleles into a population causes an increase in fitness
Decrease: Mating causes gene flow between the central and eastern populations. Immigration from mainland introduces alleles that
decrease fitness on the island

Question 35

Evolution by natural selection involves

Answer 35

Chance: New genetic variations arise by chance
Sorting: Beneficial alleles are “sorted” and favoured by natural
selection

Question 36

Relative fitness

Answer 36

Is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

Question 37

Three modes of selection

Answer 37

Directional selection: favours individuals at one end of the phenotypic range
Disruptive selection: favours individuals at both extremes of the phenotypic range
Stabilizing selection: favours intermediate variants and acts against extreme phenotypes

Question 38

Why is adaptive evolution a continuous process?

Answer 38

Environment can change

Question 39

Balancing selection

Answer 39

occurs when natural selection
maintains stable frequencies of two or more phenotypic forms in a population

Question 40

Balancing selection includes

Answer 40

Heterozygote advantage
Frequency-dependent selection

Question 41

frequency-dependent selection

Answer 41

the fitness of a phenotype declines if it becomes too common in the population

Question 42

Heterozygote advantage

Answer 42

occurs when heterozygotes
have a higher fitness
can result from stabilizing or
directional selection

Question 43

Why Natural Selection Cannot Fashion
Perfect Organisms

Answer 43

1. Selection can act only on existing variations
2. Evolution is limited by historical constraints
3. Adaptations are often compromises
4. Chance, natural selection, and the environment interact