UNIT 7 ck12’s 5.20-5.21

Question 1

What is the Hardy-Weinberg theorem?

Answer 1

It describes populations in which allele frequencies are not changing.

Such populations are not evolving.

Question 2

What are the four forces of evolution?

Answer 2

• Mutation
• Gene flow
• Genetic drift
• Natural selection

These forces cause allele frequencies to change.

Question 3

How do mutations contribute to evolution?

Answer 3

They create new genetic variations in a gene pool.

Mutations provide the genetic variation needed for other forces of evolution to act.

Question 4

In which type of species do mutations that matter for evolution occur?

Answer 4

In sexually reproducing species.

These mutations occur in gametes and can be passed to offspring.

Question 5

What is gene flow?

Answer 5

It occurs when individuals move into or out of a population.

High rates of migration can significantly affect allele frequencies.

Question 6

How can gene flow change allele frequencies?

Answer 6

By affecting both the population they leave and the population they enter.

Examples include pollen or seeds carried by wind or animals.

Question 7

What is an example of gene flow in human history?

Answer 7

Countless migrations.

Gene flow continues to mix gene pools and cause microevolutionary changes.

Question 8

What is genetic drift?

Answer 8

A random change in allele frequencies that occurs in a small population

Genetic drift can lead to significant changes in a population’s genetic makeup over time.

Question 9

How does genetic drift affect allele frequencies in offspring?

Answer 9

Allele frequencies in the offspring may differ, by chance, from allele frequencies in the parents

This can lead to unexpected genetic variations in small populations.

Question 10

What are the two special conditions under which genetic drift occurs?

Answer 10

Bottleneck effect and founder effect

These conditions can significantly influence the genetic diversity of a population.

Question 11

What is the bottleneck effect?

Answer 11

Occurs when a population suddenly gets much smaller

This can result from events like natural disasters, leading to a loss of genetic diversity.

Question 12

What can cause the bottleneck effect?

Answer 12

Natural disasters such as a forest fire or a volcanic eruption

These events can drastically reduce population size and alter allele frequencies.

Question 13

How do allele frequencies change during the bottleneck effect?

Answer 13

By chance, allele frequencies of the survivors may be different from those of the original population

This random selection can lead to a significant loss of genetic variation.

Question 14

What is the founder effect?

Answer 14

Founder effect occurs when a few individuals start, or found, a new population.

This can lead to different allele frequencies compared to the original population.

Question 15

What is a consequence of the founder effect?

Answer 15

The allele frequencies of the founders may be different from allele frequencies of the population they left.

This can lead to reduced genetic variation in the new population.

Question 16

What can happen to allele frequencies due to the founder effect?

Answer 16

They may differ from the original population.

This difference is due to chance and the limited number of founders.

Question 17

What is natural selection?

Answer 17

Natural selection occurs when there are differences in fitness among members of a population.

Question 18

How does natural selection affect gene transmission to the next generation?

Answer 18

Some individuals pass more genes to the next generation.

Question 19

What is the genotype for normal hemoglobin?

Answer 19

AA

AA genotype has 100% normal hemoglobin.

Question 20

What is the fitness level of genotype AA?

Answer 20

Somewhat reduced fitness because of no resistance to malaria

Individuals with AA genotype do not have sickle-cell anemia but lack malaria resistance.

Question 21

What is the genotype associated with the highest fitness due to malaria resistance?

Answer 21

AS

AS genotype provides enough normal hemoglobin to prevent sickle-cell anemia and offers resistance to malaria.

Question 22

What is the genotype for sickle-cell anemia?

Answer 22

SS

SS genotype results in 100% abnormal hemoglobin, leading to sickle-cell anemia.

Question 23

What is the fitness level of genotype SS?

Answer 23

Greatly reduced fitness because of sickle-cell anemia

Individuals with SS genotype suffer from severe health issues due to sickle-cell anemia.

Question 24

What is the allele responsible for sickle-cell anemia?

Answer 24

S

The S allele is an autosomal recessive allele causing sickle-cell anemia.

Question 25

What disease is caused by the Plasmodium protozoa?

Answer 25

Malaria ## Footnote Malaria is a tropical disease transmitted by mosquito bites.

Question 26

How do parasites cause symptoms in malaria?

Answer 26

By infecting the host's red blood cells ## Footnote Symptoms include fever, joint pain, anemia, and fatigue.

Question 27

What advantage do heterozygotes (AS) have in relation to malaria?

Answer 27

They are resistant to malaria ## Footnote This resistance increases their chances of survival and reproduction.

Question 28

How does natural selection maintain the S allele in the gene pool?

Answer 28

Through the survival advantage of heterozygotes ## Footnote Heterozygotes are more likely to survive malaria, allowing the S allele to persist.

Question 29

What does the sickle-cell example illustrate about fitness?

Answer 29

Fitness depends on phenotypes and may depend on the environment.

Question 30

What might happen if malaria was eliminated in an African population with a high frequency of the S allele?

Answer 30

The fitness of different genotypes may change, affecting the frequency of the S allele.

Question 31

What makes natural selection for polygenic traits more complex?

Answer 31

Natural selection for polygenic traits is more complex unless focusing on phenotypes.

Question 32

What are the three ways that natural selection can affect the phenotype of polygenic traits?

Answer 32

* Stabilizing selection * Directional selection * Disruptive selection

Question 33

What is stabilizing selection?

Answer 33

Stabilizing selection occurs when phenotypes at both extremes of the phenotypic distribution are selected against, narrowing the range of variation. ## Footnote An example is human birth weight, where very large or very small babies are less likely to survive.

Question 34

What is directional selection?

Answer 34

Directional selection occurs when one of two extreme phenotypes is selected for, shifting the distribution toward that extreme. ## Footnote This was observed in the beak size of Galápagos finches by the Grants.

Question 35

What is disruptive selection?

Answer 35

Disruptive selection occurs when phenotypes in the middle of the range are selected against, resulting in two overlapping phenotypes at each end of the distribution. ## Footnote An example is sexual dimorphism, where males and females of the same species exhibit different phenotypes.

Question 36

True or False: Stabilizing selection increases the range of phenotypic variation.

Answer 36

False