Ch 21: The Evolution of Populations

Question 1

Each organism’s traits affect its survival and ________ ______ compared with that of other individuals.

Answer 1

reproductive success p. 420

Question 2

Define microevolution.

Answer 2

A change in allele frequencies in a population over generations. p. 421

Question 3

Natural selection is not the only thing that causes microevolution. In fact, there are 3 main mechanisms that can cause allele frequency change:

Answer 3

natural selection genetic drift gene flow p. 421

Question 4

Define genetic drift.

Answer 4

chance events that alter allele frequencies p. 421

Question 5

What did Darwin not know about?

Answer 5

genes p. 421

Question 6

Some heritable phenotypic differences occur on an “either-or” basis, such as the flower color of Mendel’s pea plants: each plant had flowers that were either purple or white. Characteristics that vary this way are typically determined by a single gene _____, with different alleles producing distinct phenotypes.

Answer 6

locus p. 421

Question 7

Many phenotypic characteristics are influenced by multiple genes, including coat color in humans, seed number in maize (corn), and ______ in humans.

Answer 7

height p. 421

Question 8

In a population that is not evolving, allele and genotype frequencies will remain constant from generation to generation, provided the only Mendelian segregation and re-combination of alleles are at work. Such a population is said to be in _____-________ equilibrium.

Answer 8

Hardy-Weinberg p. 424

Question 9

The equation for Hardy-Weinberg equilibrium states that at a locus for two alleles, the three genotypes will appear in the following proportions:

Answer 9

p² (expected frequency of genotype C^RC^R) + 2pq (expected frequency of genotype C^RC^W) + q² (expected frequency of genotype C^WC^W) = 1

Question 10

The Hardy-Weinberg equilibrium describes a non-evolving population. Name the 5 conditions for Hardy-Weinberg equilibrium.

Answer 10

1. No mutations
2. Random mating
3. No natural selection
4. Extremely large population size
5. No gene flow

Inheritance must also be Mendelian (see Ch 11).

Question 11

Use the Hardy-Weinberg equation in the following question. Recall that there is one PKU occurrence per 10,000 births, which indicates that q² = ?

Answer 11

0. 0001
   p. 426

Question 12

What is macroevolution?

Answer 12

appearance/ disappearance of taxa (e.g. appearance of new genera, new families)

Question 13

What is the difference between a gene and a locus?

Answer 13

A gene is a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA).

A locus is the specific place along the length of a chromosome where a given gene is located.

Think of the locus as the gene’s address.

Question 14

Define diploid vs haploid.

Answer 14

A cell containing two sets of chromosomes, one set inherited from each parent.

Haploid cells have only one set of chromosomes.

Question 15

How many alleles can there be in a population?

What is the lower limit?

Answer 15

There is no upper limit.

It is possible for there to be only one allele in a population. This would imply that all individuals are homozygous and contain two of the same alleles at that locus.

Question 16

Define allele.

Answer 16

any of the alternative VERSIONS OF A GENE that may produce distinguishable phenotypic effects

Question 17

New alleles can arise by mutation, a change in the ________ ________ of an organism’s DNA.

Answer 17

nucleotide sequence

p. 422

Question 18

Even a point mutation in a gene that encodes a protein will have no effect on the protein’s function if the amino acid _________ is not changed.

Answer 18

composition

p. 422

Question 19

Note that in multicellular organisms, only mutations in cell lines that produce gametes can be….

Answer 19

…..passed to offspring.

p. 423

Question 20

In most animals, the majority of mutations occur in _______ cells and are not passed to offspring.

Answer 20

somatic

p. 423

Question 21

What is the only mechanism that regularly causes adaptive evolution?

Answer 21

natural selection

(Dr. Nelson, Lecture #4)

Question 22

What is needed for natural selection to cause evolution in a population?

Answer 22

1. variation in the phenotype.
2. different phenotypes –> different survival or reproductive success
3. variation in phenotype must be linked to variation in genotype (trait is heritable)

Question 23

Natural selection happens at the level of the ____________ and evolution happens at the level of the __________.

Answer 23

individual

population

(quiz question from panopto lecture)

Question 24

Adaptations are often ___________ between competing selection pressures.

Answer 24

compromises

Question 25

Remember that natural selection, gene flow, and genetic drift are all happening ______________.

Answer 25

simultaneously

Question 26

Natural selection affects ___________. They either live or die, reproduce or fail to reproduce. Success is affected by their phenotype (_________ traits).

Answer 26

individuals

expressed

Question 27

Only natural selection results in __________ to the environment.

Answer 27

adaptations

Question 28

In large populations, genetic drift’s effects are not that significant, but in _____ populations, its effects can be _____.

In conservation biology, genetic drift is very important bc those are small populations.

Answer 28

small

large

Question 29

Genetic drift can often result in loss of genetic _________. It can also cause harmful effects to become fixed in the population.

Answer 29

variation

Question 30

What is the bottleneck effect?

Answer 30

When a sudden change in the environment causes a large population to shrink to a very small size.

p. 429

Question 31

What is the name of the effect when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population?

Answer 31

the founder effect

Question 32

Gene flow is defined as…..

Note than gene flow will not ever be referred to as migration.

Answer 32

….the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.

p. 430

Question 33

Unbanded snakes on the island can avoid predation because they are camouflaged on the rocks.

On the mainland, snakes with bands are camouflaged in marshes.

If natural selection alone was operating in these populations and there was no gene flow, predict what the populations would look like….

Answer 33

…island populations have only unbanded snakes; mainlaid populations have only banded snakes.

Question 34

Gene flow from the mainland to islands (snakes can swim) _______ the effect of natural selection on evolution of the snake populations.

Answer 34

***

Question 35

Gene flow can be used to counteract negative effects of genetic drift.

Reduced genetic diversity lowers _______.

This is why in captive breeding programs, other zoos or facilities must cooperate which each other to breed animals.

Answer 35

fitness

Question 36

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus…

Answer 36

…the allele’s frequency should not change from one generation to the next.

Question 37

Relative fitness is the contribution an individual makes to the ____ ____ of the next generation relative to the contributions of other individuals.

Answer 37

gene pool

p. 432

Question 38

_______ _______ occurs when conditions favor individuals exhibiting one extreme of a phenotypic range, thereby “shifting the mean” in one direction.

Answer 38

Directional selection

p. 432

Question 39

In ________-________ selection, the fitness of a phenotype depends on how common it is in the population. In the case of the right-mouthed or left-mouthed fish, selection favored whichever phenotype was least common. Over time, the more rare phenotype becomes more common, and the common phenotype becomes rare, thus the advantage would shift to the more rare phenotype.

Answer 39

frequency-dependent

p. 436

Question 40

What prevents natural selection from reducing the variation in a population by culling all unfavorable alleles? In diploid organisms, many unfavorable recessive alleles persist because they are hidden from selection when in heterozygous individuals. Selection itself may preserve variation at some loci, thus maintaining two or more phenotypic forms in a population. This is called balancing selection, and it includes __________ ___________ and __________-________ selection.

Answer 40

heterozygote advantage and frequency-dependent selection

p. 433

Question 41

Consider a population in Hardy-Weinberg equilibrium for a character trait with these genotypic frequencies: AA = 0.25, Aa = 0.50 and aa = 0.25. If you remove all the homozygous dominants and allow the remaining population to reproduce (again under Hardy-Weinberg conditions), what will be the frequency of homozygous dominants in the next generation?

Answer 41

The new frequencies of the three genotypes are: AA = 0, Aa = 0.66 and aa = 0.33. If there were 100 individuals (carrying 200 alleles), 66/200 alleles would be A and p = 0.33. The frequency of homozygous dominant individuals would then be p², or 0.11.

Question 42

In a certain group of African people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group is heterozygous and, thus, resistant to malaria?

Answer 42

The 4% born with sickle-cell disease are homozygous for the sickle hemoglobin allele, so q² = 0.04 and q = 0.2. Because p = 1 - q, p = 0.8. The heterozygotes would be equal to 2pq, or 0.32.

Question 43

In the Hardy-Weinberg equation, p represents the ________ of allele A (dominant allele) in a population.

p² represents…..

Answer 43

frequency

the # of homozygous dominant genotypes.

Question 44

In the Hardy-Weinberg equation, q represents the ________ of allele a (recessive allele) in a population.

q² represents….

Answer 44

frequency

….the frequency of the homozygous recessive genotypes in the population.

p. 425

Question 45

In the Hardy-Weinberg equation, 2pq represents…..

Answer 45

…..the frequency of heterozygous genotypes in the population.