Evolution of Populations

Question 1

What is a common misconception about evolution?

Answer 1

That individual organisms evolve - natural selection acts on individuals, but only populations evolve

Question 2

What would happen to a population of medium found finches during a drought?

Answer 2

The large-beak birds are more likely to crack large seeds and survive - the finch population evolves, not its individual members

Question 3

What makes evolution possible?

Answer 3

Genetic variation
Variation in heritable traits is prerequisite for evolution by natural selection
Phenotype is the product of inherited genotype and environmental influences
Natural selection can only act on variation with a genetic component

Question 4

What can genetic variation be measured as?

Answer 4

Gene variability or nucleotide variability
For gene variability, average heterozygosity measures the average percent of loci that are heterozygous in a population

Question 5

What does the site of nucleotide variation dictate?

Answer 5

The site of nucleotide variation dictates the likelihood of phenotypic variation
Differences occur in non coding regions (introns) less likely to have an effect
Variations that occur in coding regions (exons) ‘can’ change the amino acid sequences of the coded protein

Question 6

What are the major sources of genetic variation?

Answer 6

Sexual reproduction can result in genetic variation by recombining existing alleles
New genes and alleles can arise by mutation or gene duplication

Question 7

What three random sources create fresh assortments of existing alleles every generation?

Answer 7

• crossing over
• independent orientation of homologous chromosomes at metaphase 1 of meiosis
• random fertilization

Question 8

What serves as the raw material for evolution?

Answer 8

Mutations -creation of new alleles
- mutations are a “two-edged sword,” most being deleterious or neutral
- some mutations can be beneficial in instances when environment is changing such that mutations that were once disadvantageous are favorable under new conditions

Question 9

What are the five main kinds of mutations?

Answer 9

• point mutations
• insertion / deletions (“indels”)
• gene duplication
• chromosome inversions
• polyploidization

Question 10

Point mutation

Answer 10

Single-base substitutions caused by DNA polymerase errors in either:
- DNA synthesis
- DNA repair
Often referred to as Single Nucleotide Polymerase or SNPs

Question 11

What does redundancy in genetic code allow for?

Answer 11

It allows for silent mutations to persist

Question 12

Silent mutations

Answer 12

Have no effect at all on the genetic code

Question 13

Missense mutation

Answer 13

Change the amino acid coding, produces a different amino acid
Leads to a base substitution that produces an improved protein that enhances the success of the mutant organism and its descendant

Question 14

Nonsense mutation

Answer 14

Changing of an amino acid into a stop codon

Question 15

What can deletion/insertion mutations result in?

Answer 15

• altering of the reading frame of the mRNA, so that nucleotides are grouped into different codons
• lead to significant changes in amino acid sequence downstrene of the mutation
• produce a nonfunctional polypeptide

Question 16

A deletion

Answer 16

The loss of a chromosomal segment

Question 17

A duplication

Answer 17

The repeat of a chromosome segment

Question 18

An inversion

Answer 18

The reversal of a chromosome segment

Question 19

A translocation

Answer 19

The attachment of a segment to a non homologous chromosome that can be reciprocal

Question 20

Polyploidization

Answer 20

• polyploid organisms have more than 2 sets of chromosomes
• polyploidy usually occurs because of a failure in reduction division at meiosis which results in a 2n gamete

Question 21

How do mutation rates vary across organisms?

Answer 21

• mutation rates are low in animals and plants
• the average is about one mutation in every 100,000 genes per generation
• mutation rates are often lower in prokaryotes, but short generation time allow mutations to accumulate rapidly
• viruses have both high mutation rates and short generation times - hence new flue vaccine every year

Question 22

What is the Lenski long-term evolution experiment?

Answer 22

The E. Coli long-term evolution experiment is an ongoing study in experimental evolution led by Richard Lenski that has been tracking genetic changes in 12 initially identical populations of asexual bacteria since 24 February 1988
The populations are now approaching 100,000 generations

Question 23

A population

Answer 23

A group of individuals of the same species, that live in the same area, and interbreed

Question 24

A gene pool

Answer 24

Consists of all the alleles for all loci in a population

Question 25

A locus

Answer 25

Fixed if all individuals in a population are homozygous for the same allele

Question 26

What happens if there are two or more alleles for a locus?

Answer 26

Diploid individuals may be either homologous or heterozygous

Question 27

How can we measure evolution?

Answer 27

We can measure evolution as a change i the prevalence of certain heritable traits in a population over a spa of generations

Question 28

Is there a change in the relative frequencies of alleles in a population over a number of generations?

Answer 28

Termed micro-evolution - evolution occurring on its smallest scale

Question 29

The Hardy-Weinberg principle

Answer 29

The shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population

Question 30

What does the Hardy-Weinberg equation describe?

Answer 30

The genetic makeup we expect for a population that is not evolving at a particular locus

Question 31

What does the observed frequencies not matching the expected suggest?

Answer 31

According to Hardy-Weinberg, it suggests that the population may be evolving

Question 32

What five conditions must be satisfied for a population to be in Hardy-Weinberg equilibrium?

Answer 32

• a very large population
• no gene flow between populations
• no mutation
• random mating
• no natural selection

Question 33

What three major factors alter allele frequencies and bring about most evolutionary change?

Answer 33

• natural selection
• genetic drift
• gene flow

Question 34

Natural selection

Answer 34

If individuals differ in their survival and reproduction success, natural selection will alter allele frequencies

Question 35

Random genetic drift

Answer 35

• one Hardy-Weinberg assumption is that populations are a large size
• in a process called genetic drift, chance events can cause allele frequencies to fluctuate unpredictably form one generation to the next
• the smaller the population, the more impact genetic drift is likely to have
• can result in maladaptive changes in allele frequency

Question 36

What can sampling errors do in finite populations?

Answer 36

They can alter allele frequencies in finite populations

Question 37

Founders effect

Answer 37

When a few individuals colonize an island or other new habitat
- the smaller the group, the less likely the genetic makeup of the colonists will represent the gene pool of the larger population they left

Question 38

Bottleneck effect

Answer 38

Occurs when there is a drastic reduction in population size due to a sudden change in the environment
- the resulting gene pool may no longer be reflective of the original population’s gene pool and results in genetic drift

Question 39

Gene flow

Answer 39

• allele frequencies in a population can also change as a result of gene flow, where a population may gain to lose alleles when fertile individuals move into or out of a population or when gametes (such as plant pollen) are transferred between populations.
• gene flow tends to reduce differences between populations
• restrictions to gene flow tends to favor the formation of new species

Question 40

What mechanism consistently leads to adaptive evolution?

Answer 40

Natural selection is the only mechanism that consistently leads to adaptive evolution
- it’s only by chance that events such as genetic drift, gene flow, and mutations improve a populations fit or it’s environment
- some individuals are more likely than others to survive and reproduce
- natural selection is not random
- surviving individuals have a feared relative fitness - the contribution an individual makes to the gene. Pool of the next generation relative to others

Question 41

What are the three variations of ways natural selection and alter a population?

Answer 41

• stabilizing selection
• directional selection
• disruptive selection

Question 42

Sexual selection

Answer 42

A form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mares - can lead to sexual dimorphism

Question 43

Intrasexual sexual selection

Answer 43

Individuals of one sec compete for mates

Question 44

Intersexual selection

Answer 44

Mate choice

Question 45

What is the advantage to females of being chooses?

Answer 45

One hypothesis is that females prefer male traits that are correlated with “good genes”

Question 46

Trade offs for the male

Answer 46

Susceptibility to predators

Question 47

Why aren’t less adaptive alleles eliminated as the “best” alleles are passed to the next generation?

Answer 47

Natural selection acts on phenotype and so in diploid organisms recessive alleles can “hide” in heterozygous and be protected from natural selection

Question 48

Balancing selection

Answer 48

Occurs sub natural selection maintains stable frequencies of two or more phenotypic forms in a population
- example: Heterozygous advantage - heterozygotes have greater success than either homozygote

Question 49

Frequency- dependent selection

Answer 49

Acts against either phenotype if it becomes too common

Question 50

What are the four “better than” basis’ of evolution?

Answer 50

• selection can act only on existing variations. New, advantageous alleles do not arise on demand
• evolution is limited by historical constraints. Evolution co-opts existing structures and adapts them to new situations
• adaptations are often compromises. Specialization in one trait often has costs
• chance, natural selection, and the environment interact. Environments often change unpredictably