1. Introduction to Biology

2. Chemistry

3. Water

4. Biomolecules

5. Cell Components

6. The Membrane

7. Energy and Metabolism

8. Respiration

9. Photosynthesis

10. Cell Signaling

11. Cell Division

12. Meiosis

13. Mendelian Genetics

14. DNA Synthesis

15. Gene Expression

16. Regulation of Expression

17. Viruses

18. Biotechnology

19. Genomics

20. Development

21. Evolution by Natural Selection

22. Evolution of Populations

23. Speciation

24. History of Life on Earth

25. Phylogeny

26. Prokaryotes

27. Protists

28. Plants

29. Fungi

30. Overview of Animals

31. Invertebrates

32. Vertebrates

33. Plant Anatomy

34. Vascular Plant Transport

35. Soil

36. Plant Reproduction

37. Plant Sensation and Response

38. Animal Form and Function

39. Digestive System

40. Circulatory System

41. Immune System

42. Osmoregulation and Excretion

43. Endocrine System

44. Animal Reproduction

45. Nervous System

46. Sensory Systems

47. Muscle Systems

48. Ecology

49. Animal Behavior

50. Population Ecology

51. Community Ecology

52. Ecosystems

53. Conservation Biology

[BOOK BIO] CLUTCH

The Evolution of Populations: Natural Selection, Genetic Drift, and Gene Flow

Suppose you were studying several species of monkeys. In one, males never helped females raise offspring. In another, males provided just as much parental care as females except for actually carrying the fetus during pregnancy. How does the fundamental asymmetry of sex compare in the two species? How would you expect sexual dimorphism to compare between the two species?

No. Stabilizing selection occurs in stable environments, which resist factors that promote phenotypic variation.

No. Antibiotic resistance acts opposite to disruptive selection in that it promotes the growth of only those bacteria with the resistant gene.

No. This situation represents rapid evolution rather than equilibrium.

No. The spread of antibiotic resistance in a population would be an example of microevolution.

Consider how the distribution of the trait is being affected.

Antibiotic resistance in bacteria is an example of which of the following?

How strong the organism is when pitted against others of its species

No. This is not a generic measurement of fitness because not all organisms compete in this way.

Its ability to withstand environmental extremes

No. But that might increase its fitness because it may be able to leave more offspring than other individuals.

How much food it is able to make or obtain

Consider how a population changes.

Which of the following most accurately measures an organism's fitness?

Only random mating takes place among all the people that reproduce in North America.

No. That would decrease the possibility of microevolution in that population.

The incidence of skin cancer in adults over age 40 rises significantly.

No. Skin cells are somatic cells and would not affect reproduction.

Hundreds of thousands of people are killed in a natural disaster.

No. That would not be a significant enough change in the human gene pool to cause microevolution to take place.

A colony of humans on the moon is isolated from Earth.

Consider the Hardy-Weinberg assumptions.

Which of the following scenarios would most likely result in the microevolution of a population of humans?

humans will become tolerant to the effects of drugs

No. Consider why antibiotics are prescribed.

the organisms that produce many of the antibiotics are overexploited and could become extinct

the drugs will be metabolized more quickly by our bodies, decreasing their effectiveness

No. This is possible, but it is not the major cause for concern.

strains of microorganisms that are resistant to these drugs will be selected for

Consider the directional mode of natural selection.

For several years, scientists have warned doctors of the danger of overprescribing antibiotics such as penicillin. Scientists are concerned because __________.

Inbreeding and Sexual Selection

Natural Selection - Crash Course Biology #14

How do the phospholipids in archaea differ from those in other cells?
a. They have tails made of unsaturated fatty acids instead of saturated fatty acids.
b. They do not contain hydrocarbon chains.
c. They have isoprenoid tails instead of fatty acid tails.
d. They have two hydrocarbon chains instead of three hydrocarbon chains.

BioFlix: Natural Selection

Genetic Drift | Founder Effect and Bottleneck Effect Explained

individual mosquitoes built up an immunity to an insecticide after being exposed to it

No. The insecticides are toxic chemicals. The insects could not have developed immunity.

mosquitoes needed to develop insecticide resistance to survive after the insecticide was used

No. This is not how evolution works. Selection can only edit existing variations.

mosquitoes attempted to adapt to their environment

No. Mosquitoes are not capable of such an action.

a new allele developed in response to the insecticide that provided future generations the benefit of resistance

No. This is not how evolution works. New alleles do not arise on demand.

a few mosquitoes were probably resistant to the insecticide before it was ever used, and these individuals were more likely to survive and reproduce in the presence of insecticide

Does insecticide kill all members of a mosquito population? .

A number of mosquito populations today are resistant to insecticides that were once quite effective. Biologists think that insecticide resistance evolved in mosquitoes because __________.

True or false? Gene flow can either increase or decrease the average fitness of a population. Explain.

Heterozygous Advantage

According to the RNA world model, a ribozyme would replicate by creating a double-stranded RNA intermediate. Would you expect the intermediate to have the same catalytic activity as the original ribozyme? Justify your answer with an explanation.

Genetic drift, bottleneck effect and founder effect | Biology | Khan Academy

Directional, Stabilizing, and Disruptive Seleciton

STABILIZING, DIRECTIONAL, DISRUPTIVE SELECTION

Homozygosity in some prairie chicken populations

No. These populations have almost no genetic variation.

Polymorphism of the Gal&#225;pagos finches

No. These variations are adaptive and selective rather than neutral.

No. The founder effect reduces the amount of variation in a population, but there is no reason to assume the variations are neutral.

No. Colors usually have a purpose, such as mating or camouflage.

Consider which of these does not affect fitness.

Which of the following would seem to be an example of neutral variation?

No. Chromosomes are duplicated but not shuffled in mitosis.

No. This is the random change in a small gene pool.

No. Natural selection refers to an organism's reproductive success.

No. Mutation is the ultimate source of genetic variation, but it has nothing to do with sexual recombination.

Consider when genetic recombination occurs.

Sexual recombination includes the shuffling of chromosomes in __________ and fertilization.

Evaluate the following statements related to the synthesis of nucleic acids. Select True or False for each statement.
T/F Ribonucleotides are added to the 3′ end of a DNA strand.
T/F Polymerization of nucleic acids occurs by the formation of phosphodiester bonds.
T/F Complementary pairing between sugars is required for copying nucleic acids.
T/F Strands in a double helix are synthesized in an antiparallel orientation.

No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is
a. new mutations that occurred in the preceding generation.
b. genetic drift.
c. the reshuffling of alleles in sexual reproduction.
d. environmental effects.

Mechanisms of Natural Selection Part 1: Types of Sexual Selection

No. Stabilizing selection favors intermediate variants.

No. Directional selection acts against individuals at one of the phenotypic extremes.

No. Balancing selection maintains stable frequencies of two or more phenotypic forms in a population.

No. The type of selection referred to in the question would favor evolution rather than equilibrium.

Consider the effect of the predation on the trait distribution.

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

DNA forensics relies on neutral variation among humans.

No. DNA forensics does use neutral variation to distinguish one human from another, but this use of neutral variation does not affect evolution.

Relative frequencies of neutral variations are controlled by natural selection.

No. Variations are considered neutral if they are neither advantageous nor deleterious. Natural selection does not act on variation that is neutral in the current environment.

Neutral variation is usually removed from the population by natural selection because it does not confer an advantage in the current environment.

No. Natural selection does not act on neutral variation.

Many mutations are silent and do not affect the amino acid that is coded for.

No. Although this statement is true, it does not explain the importance of this kind of variation to evolution.

Neutral variation increases genetic variation, allowing a population to carry more alleles that may help it respond to environmental change.

Is neutral variation always neutral?

What is the importance of neutral variation in evolution?

The largest unit within which gene flow can readily occur is a
a. population.
b. species.
c. genus.
d. hybrid.

A new plant species C, which formed from hybridization of species A(2n = 16) with species B(2n = 12), would probably produce gametes with a chromosome number of
a. 12.
b. 14.
c. 16.
d. 28.

In an area of erratic rainfall, a biologist found that grass plants with alleles for curled leaves reproduced better in dry years, and plants with alleles for flat leaves reproduced better in wet years. This situation would tend to _________ . (Explain your answer.)
a. cause genetic drift in the grass population.
b. preserve genetic variation in the grass population.
c. lead to stabilizing selection in the grass population.
d. lead to uniformity in the grass population.

Natural selection changes allele frequencies because some _________ survive and reproduce better than others.
a. alleles
b. loci
c. species
d. individuals

Balancing Selection and Gene Flow

Animation: Causes of Evolutionary Change

Cooking oil lipids consist of long, unsaturated hydrocarbon chains. Would you expect these molecules to form membranes spontaneously? Why or why not? Describe, on a molecular level, how you would expect these lipids to behave in water.

If nucleotides from the DNA of a human were quantified and 30 percent of them contained the base adenine, what percentage of them would contain the base guanine?
a. 20 percent
b. 30 percent
c. 40 percent
d. 70 percent

Ivory from elephant tusks is a valuable commodity on the world market. As a result, male African elephants with large tusks have been heavily hunted for the past few centuries. Today, male elephants have significantly shorter tusks at full adulthood than male elephants in the early 1900s. This is an example of                   .
a. diversifying selection;
b. stabilizing selection;
c. directional selection;
d. chance;
e. more than one of the above is correct

Describe three ways that evolution can occur via genetic drift.

No. The founder effect, another example of genetic drift, would occur if a small group of lizards migrated to the island.

No. Gene flow would occur if lizards migrated in and out of the population.

No. There are no mutations described here.

No. There is no indication that the lizards that survived did so because of any beneficial trait.

What are some of the mechanisms that change allele frequencies?

An earthquake hits a small island. All but a small group of closely related lizards are eliminated, and the survivors spread out over the island. This is an instance of __________.

Genetic Drift

Why is genetic drift aptly named? Select True or False for each statement.

T/F It causes allele frequencies to drift up or down randomly.
T/F It occurs when alleles from one population drift into another.
T/F It occurs when mutations drift into a genome.

The risks faced by small populations include                   .
a. erosion of genetic variability through genetic drift;
b. decreased fitness of individuals as a result of inbreeding;
c. increased risk of experiencing natural disasters;
d. A and B are correct;
e. A, B, and C are correct

No. This refers to genetic variations that have little or no impact on reproductive success.

No. This answer is too specific. Heterozygote advantage is just one mechanism of balancing selection.

No. This mode of selection actually reduces variation and maintains the status quo for a particular phenotypic character.

No. Directional selection is selection for a single form; selection for two or more forms is balancing selection.

Review the types of selection. .

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population?

Which of these functional groups is known to be used for storing large amounts of chemical energy?
a. amino group
b. carbonyl group
c. phosphate group
d. sulfhydryl group

Evaluate this statement: Gene flow increases the genetic divergence of populations.

Genetic variation, gene flow, and new species

Antibiotic resistance is becoming common among organisms that cause a variety of human diseases. All of the following strategies help reduce the risk of antibiotic resistance evolving in a susceptible bacterial population except                   .
a. using antibiotics only when appropriate, for bacterial infections that are not clearing up naturally;
b. using the drugs as directed, taking all the antibiotic over the course of days prescribed;
c. using more than one antibiotic at a time for difficult-to-treat organisms;
d. preventing natural selection by reducing the amount of evolution the organisms can perform;
e. reducing the use of antibiotics in non–health-care settings, such as agriculture

Intrasexual selection leads to the death of most unfit males in combat.

No. More often than not, the victor of these struggles wins through psychological methods rather than physical ones.

Showy secondary sexual characteristics cannot be explained because they break all of the rules of natural selection.

No. On the surface, this does appear to be true. For example, the colorful plumage of some birds makes them much more visible to predators. However, there are some theories to explain how these characteristics can increase an individual's fitness.

In most vertebrates, females court the males.

No. Males are usually the suitors in vertebrate populations.

There is no evidence that intrasexual selection takes place between females.

No. There is evidence in some populations of females establishing hierarchies of dominance.

Sexual selection can result in sexual dimorphism&mdash;marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction.

Remember that organisms are successful if they survive and reproduce.

Which statement below is true about sexual selection?

Types of Natural Selection

No. This would slightly decrease the number of genes in the gene pool.

No. Because the genetic code is redundant, even point mutations in genes that code for proteins may have little effect if they do not alter the amino acid composition. The chances are slight that such a mutation would have a profound effect on an organism.

No. Such a mutation would most likely be harmful, and it does not generate new genetic material.

No. A change in nucleotide sequence describes the result of any type of mutation but is not in and of itself a type of mutation.

Think about the end result of different types of mutations.

Which type of mutation plays the most important role in increasing the number of genes in the gene pool?

What would be the sequence of the strand of DNA that is made from the following template: 5′-GATATCGAT-3′? (Your answer must be written 5'→3'.) How would the sequence be different if RNA were made from this DNA template?

Draw a small concept map showing how selection, genetic drift, gene flow, and mutation relate to genetic variation.

No. Natural selection leads to adaptation, but it is not the origin of genetic variation.

No. This just leads to a change in the frequency of alleles in a gene pool.

No. Sexual recombination does not generate new alleles; it merely recombines available alleles.

No. The environment elicits adaptation but not genetic variation.

Only one of these choices actually introduces new alleles into a population.

Which of the following mechanisms can form entirely new alleles?

A horse (2n = 64) and a donkey (2n = 62) can mate and produce a mule. How many chromosomes would there be in a mule's body cells?
a. 31
b. 62
c. 63
d. 126

Heterozygote Advantage

Natural Selection animation (stabilizing, disruptive and directional selection)

Genetic drift; natural selection; mutation