Natural Selection, Fitness, & Adaptation

Question 1

Natural selection

Answer 1

Process by which adaptive structures are evolved and maintained

Question 2

What is regarded as the main cause of change in organisms in relation to their environment?

Answer 2

Natural selection

Question 3

Natural selection depends on ______

Answer 3

genetic variations, which originate idiosyncratically by mutation and recombination

Question 4

The biased reproduction of certain genetic alternatives based on an organism’s characteristics and interactions

Answer 4

Natural selection

Question 5

Conditions for natural selection to operate

Answer 5

1.) The individuals or units of selection must vary
2.) Some individuals must be more fit than others (differential fitness)
3.) There must be a correlation between the fitness of parents and offspring (heritability)

Question 6

5 Observations in Origin

Answer 6

1.) Populations have the potential to increase exponentially
2.) But they generally maintain a stable size
3.) Resources are limited
[Struggle for existence]

4.) Variation in all species
5) Variation is heritable
[Variation makes some individuals more successful than others in the struggle; those that survive and reproduce will leave offspring that have those same variants]

*Evolution by natural selection

Question 7

Darwin and Wallace’s mechanism for evolution

Answer 7

Natural selection

Question 8

The phenomenon of ________ variation leading to a better chance of survival and reproduction

Answer 8

favorable

Question 9

Fitness

Answer 9

A measure of how good an organism is at survival and reproduction (“reproductive success”)
- a number

Question 10

An example of natural selection in finches

Answer 10

Variation in beak size and shape in a single species of ground finch
Factors: annual rainfall and number of cactus flowers by year

Variation in beak shape
- long and thin to short and thick

Beak shape affected food resource possibilities
- nectar of flowers
- bugs inside cactus paddles

El Niño event in 1983
- most cactuses fell over and rotted, causing beak size to evolve from long and thin to SHORT and THICK

Question 11

Favorable

Answer 11

= higher relative fitness

Question 12

Variation is not inherently “good” or “bad”

Answer 12

A variant that has high fitness in one environment might not have high fitness in another different environment
- the fitness value associated with a phenotype/genotype is ENVIRONMENTALLY DEPENDENT!

Question 13

Selected for

Answer 13

Higher relative fitness

Question 14

Selected against

Answer 14

Lower relative fitness

Question 15

How is fitness a weighting factor?

Answer 15

Determines how quickly evolution will happen

Question 16

Adaptation

Answer 16

The phenomenon of an organism being a good “fit” to its environment

Question 17

Natural selection produces…

Answer 17

adaptation

Question 18

Key points about adaptation

Answer 18

1.) Trait that increases the reproductive success of an organism
2.) The process of genetic change of a population, owing to natural selection, whereby the average state of a character becomes improved with reference to a specific function, or whereby a population is thought to have become better suited to some feature of its environment
3.) Improvement in function
4.) The process of successful interaction between a population and an environment
5.) An anatomical physiological or behavioral response of organisms or populations to the environment

Question 19

The 3 different patterns of selection

Answer 19

1.) Directional selection
2.) Stabilizing selection
3.) Disruptive selection

Question 20

Directional selection

Answer 20

Relative fitness increases toward one extreme

Question 21

Stabilizing selection

Answer 21

Fitness is low at both extremes

Question 22

Disruptive selection

Answer 22

Relative fitness low at intermediate phenotype/genotype; high at both extremes

• relative fitness is high at both extremes but low at the initial average

Question 23

Cavet of selection

Answer 23

Sickle Cell Disease

Question 24

Why doesn’t natural selection eliminate the HbS allele if it causes Sickle Cell?

Answer 24

Heterozygote advantage

Question 25

Heterozygote advantage

Answer 25

Fitness of the heterozygotes is greater than either homozygote
- explains how a seemly deleterious allele can be maintained in a population

Question 26

The heterozygote that causes Sickle Cell has an advantage in…

Answer 26

Malaria-endemic areas

Question 27

Malaria

Answer 27

Common and deadly disease passed to humans through an insect vector
- the protozoan Plasmodium falciparum has a lifecycle partly in mosquito bodies and partly in red blood cells

Question 28

The HbA HbS heterozygotes are more resistant to developing malaria than the HbA HbA homozygotes

Answer 28

Red blood cells of heterozygotes are less hospitable for the parasite that causes Malaria

Question 29

The greater relative fitness of the HbA HbS heterozygotes PREVENTS the HbS allele form being eliminated…

Answer 29

Even though the HbS HbS condition is associated with a severe disease state and low fitness

Question 30

The hetozygote advantage can create a state of balanced polymorphism, where what happens?

Answer 30

Where multiple alleles reach a steady state distribution
- sometimes called balancing selection

Question 31

What happens when the heterozygote advantage disappears?

Answer 31

The HbS allele should be “selected against” because of the lower fitness of the HbS homozygote
- It takes a long time to eliminate a deleterious allele if reduced fitness is exhibited only by the rare deleterious allele homozygotes
- There are some studies that suggest the frequency of the HbS allele is decreasing in the US populations (because Malaria is not too common in the US so we don’t need the heterozygote advantage)

Question 32

The evolutionary history of sickle cell provides a good example of human behavior modifying evolution

Answer 32

Human populations shift to agricultural practices
- humans create malarial breeding grounds
- human population density increases

Because there is more malaria, heterozygote has even greater relative fitness
- the deleterious allele become more common in the population

Bicultural feedback
- human behavior alters environment
- New environment causes new selective pressure
- new selective pressure alters genotype frequency
- More people survive, population grows

Question 33

The Modern Synthesis

Answer 33

Period 1930s-40s marking assimilation of Darwin’s evolution (emergence of contemporary evolutionary theory)
- Re-define evolution in the framework of genetics
- creation of population genetics
- combination of mutation and natural selection causes evolution
- but there are other causes of evolution as well!

Question 34

Genetics and statistics

Answer 34

Ronald Fisher
JBS Haldane
Sewall Wright
Theodosius Dobzhansky

Question 35

Taxonomy and Systematics

Answer 35

Ernst Mayr

Question 36

Paleontology

Answer 36

G.G. Simpson

Question 37

Evolution is…

Answer 37

The transformation of species over time
- shift frequency of different variants in populations
- and the appearance of new species

a change in allele frequency in a population over time

Question 38

Population genetics

Answer 38

Field concerned with detecting and explaining how phenotype, genotype, and allele frequencies change over time (generations)
- sometimes called microevolution

Question 39

Microevolution

Answer 39

Within a species, changes in allele frequency from one generation to the next

Question 40

Evolution is defined by what?

Answer 40

Population frequencies
- Individuals do NOT evolve

Question 41

The 4 forces of evolution!

Answer 41

1.) Mutation
- source of all variation
2.) Natural selection
- shifts pattern of variation due to fitness differences
- produces adaptation
3.) Genetic drift
4.) Gene flow