Evolution and Speciation Review AP Bio

Evolution and Speciation Review

AP Biology

What is Evolution?

• EVOLUTION: the changes in allele frequency over time via natural selection; on a large scale, can lead to speciation

• ​Allele - different variations of the same gene (ex. blue eyes vs. brown eyes)

• Natural Selection - when certain traits are more ​advantageous than others, which allows organisms with those traits to survive and have more offspring

​

Changes in the gene pool --> better FITNESS (reproductive success) --> adaptations

Multiple Choice

Define allele.

• the organism that is better suited for its environment has the most reproductive success

• different variations of the same gene

• the changes in allele frequency over time

• the formation of a new species

Multiple Choice

Define survival of the fittest.

• the organism that is better suited for its environment has the most reproductive success

• different variations of the same gene

• the changes in allele frequency over time

• the formation of a new species

Multiple Choice

Define speciation.

• the organism that is better suited for its environment has the most reproductive success

• different variations of the same gene

• the changes in allele frequency over time

• the formation of a new species

Multiple Choice

Define evolution.

• the organism that is better suited for its environment has the most reproductive success

• different variations of the same gene

• the changes in allele frequency over time

• the formation of a new species

What Causes Natural Selection?

• Over-reproduction: more offspring are born than will live to maturity

  • This causes the population to exceed the carrying capacity of the ecosystem and encourages more predator-prey interactions.

• Genetic variation within a population: if all of the organisms are true breeds, they will all survive or die at the same rate

• ​Competition: individuals in a population have to compete for limited resources

• Different reproductive success​: organisms that are best fit to their environment will reproduce more and pass on those genes (survival of the fittest)

Multiple Choice

Before North America was colonized by Europeans, the North American Deer population was kept in check by wolves. Once settlers arrived they began to recognize wolves as a nuisance and danger to their communities so hunted the animals, and wolf populations were severely decreased. As a result of the loss of their main predator, the deer population began to boom. Deer feed on all sorts of plants, trees, shrubs, flowers, and grass, and require large quantities of such vegetation to sustain themselves. Eventually, deer began to starve because their large numbers depleted their main source of food; they had reached their carrying capacity.

The deer provide an example of which cause of natural selection?

• Over-reproduction

• Genetic variation within a population

• Competition

• Different reproductive success

Multiple Choice

This image is an example of which cause of natural selection?

• Over-reproduction

• Genetic variation within a population

• Competition

• Different reproductive success

Multiple Choice

In Maasi Mara, the adult male lion and spotted hyena share the same ecosystem, Hence, the two animals must compete for the same prey, both being carnivorous hunters. However, this can negatively impact the living of the other as the presence of one will bring about less food for the other.

The hyena and lions in Maasi Mara are an example of which cause of natural selection?

• Over-reproduction

• Genetic variation within a population

• Competition

• Different reproductive success

Multiple Choice

The antlers of a stag, for example—increases prowess in competition with members of the same sex. Stags, rams, and bulls use antlers or horns in contests of strength; a winning male usually secures more female mates.

The antlers or horns of male stags, rams, and bulls aid them with which example of which cause of natural selection?

• Over-reproduction

• Genetic variation within a population

• Competition

• Different reproductive success

Speciation

Speciation is the creation of new species due to the genetic changes within the population - making it impossible for them to create viable offspring with another population. This is an example of macroevolution.

​

• ​Macroevolution - evolutionary change above the species level

• Microevolution​ - changes in allele frequencies within a single gene pool

A species is defined as a population or group of populations where members have the potential to interbreed in nature and produce viable, fertile offspring.

Microevolution vs. Macroevolution

Natural selection happens on both a small scale and a large scale.

​

Microevolution is small scale and occurs in the same species or population. It is seen in nature when there is an unfilled niche in an environment that makes a new trait a better advantage (like peppered moths).

​

As these changes occur, this adds to the diversity within like-organisms. At some point, the number of genetic differences becomes so numerous that they become two separate species, which is macroevolution.​

Multiple Choice

The slight genetic changes over a few generations in a population that does NOT result in the evolution of a new species is...

• speciation

• microevolution

• macroevolution

• fertilization

Reproductive Isolation

​Reproductive isolation causes speciation. If organisms become no longer reproductively compatible (meaning they cannot produce viable, fertile offspring), then an ancestral species will branch into two new species.

​

Types of isolation:​

• Prezygotic - prevents mating or hinders fertilization

• Postzygotic​ - prevents hybrid zygote from developing into fertile adult

​Hybrid - offspring arising from 2 species mating​​

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

​

Postzygotic Barriers:

• Geographical Isolation

• Temporal Isolation

• Behavioral Isolation

• Mechanical Isolation

• Gametic Isolation

Prezygotic Barriers:

Types of Reproductive Barriers

Multiple Choice

In flowering plants, the shape of the flower will tend to match up with a natural pollinator. Plants that do not have the correct shape for the pollinator will not receive a pollen transfer.

A hummingbird trying to pollinate a foxglove flower might be an example of...

• prezygotic barrier - mechanical isolation

• prezygotic barrier - temporal isolation

• prezygotic barrier - behavioral isolation

• postzygotic barrier

Multiple Choice

It is possible for goats and sheep to mate and for fertilization to occur. But genetic differences result in a zygote that does not develop properly and will die.

The mortality of this offspring is an example of...

• prezygotic barrier - mechanical isolation

• prezygotic barrier - gametic isolation

• prezygotic barrier - behavioral isolation

• postzygotic barrier

Multiple Choice

A species of monkey that is located on an island cannot breed with another species of monkey on the mainland. The water and distance between the two species keep them isolated from one another and make it impossible for them to breed.

This situation is an example of...

• prezygotic barrier - geographic isolation

• prezygotic barrier - gametic isolation

• prezygotic barrier - behavioral isolation

• postzygotic barrier

Multiple Choice

The field crickets Gryllus pennsylvanicus and G. veleti become sexually mature at different seasons, one in the spring and the other in the autumn.

This inability of these cricket species to mate is an example of...

• prezygotic barrier - geographic isolation

• prezygotic barrier - temporal isolation

• prezygotic barrier - mechanical isolation

• postzygotic barrier

Overlapping populations within the same geographic area

​

​Gene flow between subpopulations blocked by:

• po​lyploidy

• habitat differentiation

• sexual selection​

Sympatric Speciation

Geographically isolated populations

​

• ​Caused by geologic events or processes

• Evolves by natural selection and genetic drift​

Allopatric Speciation

Types of Speciation:

Autopolyploid: an extra set of chromosomes

​

• ​Failure of cell division (2n --> 4n)

• Ex. strawberries are 4n, 6n, 8n, 10n (decaploid)​

Sympatric Speciation

Antelope squirrels on opposite rims of the Grand Canyon.

Allopatric Speciation

Examples:

Multiple Choice

A physical barrier separates a single species, causing two separate populations to form. Over time these two populations adapt to their environments. Eventually, these two populations are no longer able to successfully reproduce with each other. This is known as __________.

• sympatric speciation

• allopatric speciation

• peripatric speciation

• parapatric speciation

Multiple Choice

The Midas cichlid (species of Amphilophus), which is living in Lake Apoyo (a volcanic lake in Nicaragua), is a specific example of speciation. Scientists analyze their appearance, nature, and DNA. Although these two have similarities they are different as well and cannot cross-breed. All the available evidence indicates that one species evolved from another. The newer species of this population has evolved almost recently but if we talk about the terms of evolution, it evolved almost 10,000 years back. Which example of speciation is t

• sympatric speciation

• allopatric speciation

• peripatric speciation

• parapatric speciation

Hybrid Zones

Hybrid zones are incomplete reproductive barriers in which there are 3 possible outcomes:

• ​Reinforcement - strengthening of reproductive barriers

• Fusion - weakening of reproductive barriers

• Stability - continued formation of hybrid individuals​

Multiple Choice

What is the result of fusion that can occur in hybrid zones?

• weakening of reproductive barriers

• strengthening of reproductive barriers

• continued formation of hybrid individuals

• no change

Defined by long periods of stasis punctuated by sudden change seen in the fossil record.​

Punctuated Equilibrium

Slow, constant change developing from common ancestors.

Gradualism

Time Course of Speciation:

Multiple Choice

This graph showing morphological divergence over time is an example of which time course of speciation?

• gradualism

• punctuated equilibrium

• sympatric speciation

• allopatric speciation

Hardy-Weinberg Equilibrium

What is a gene pool?

All alleles at all loci in all of the members of a population.

​

A fixed allele occurs when all members of a population are homozygous for the same allele.

• More fixed alleles --> less genetic diversity.

Hardy-Weinberg Equilibrium

Requirements:

Hardy-Weinberg equilibrium describes a population that is not evolving. The frequencies of alleles and geotypes remain constant over generations unless acted upon by agents other than sexual recombination. The following conditions must be met:

1. No mutations​

2. Random mating (no sexual selection)

3. No natural selection

4. Extremely large population size (no genetic drift)

5. No gene flow (no emigration or immigration)​

Hardy-Weinberg Equilibrium

Equation:

Allele Frequencies:

• Genes with 2 alleles: p, q

  • p = frequency of A (dominant allele)

  • q = frequency of a (recessive allele)​

​

Genotype Frequencies:

• 3 genotypes: AA, Aa, aa

  • p² = AA (homozygous dominant)

  • 2pq = Aa (heterozygous)

  • q² = aa (homozygous recessive)​

​

Multiple Choice

Suppose in a plant population, red flowers (R) is dominant to white flowers (r). In a population of 500 individuals, 25% show the recessive phenotype. How many individuals would you expect to be homozygous dominant and heterozygous for this trait?

• 250 individuals

• 125 individuals

• 375 individuals

• .5 individuals

Multiple Choice

There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a grade of F. Sorry. In the highly unlikely event that these traits are genetic rather than environmental, if these traits involve dominant and recessive alleles, and if the four (4%) represent the frequency of the homozygous recessive condition, please calculate the frequency of the recessive allele.

• 0.2

• 0.8

• 0.04

• 0.96

Driving Forces of Evolution

Mutations are the ONLY source of NEW genes and NEW alleles.

• Mutations in gametes can be passed to offspring.

• Point mutations can occur in individuals.

• Chromosomal mutations can result in gene duplication.

​

In prokaryotes, reproduction is fast, so mutations can quickly generate genetic variation. In eukaryotes, sexual reproduction occurs, which shuffles all of the existing alleles (crossing over, independent assortment, random fertilization)​

Mutations Rates

 Plants/Animals- 1/100,000 genes per generation

 Prokaryotes- fewer mutations, shorter generation span, more genetic variation

 Viruses- more mutations, shorter generation span,RNA genome with fewer repair mechanisms

Multiple Choice

Which of the following is most affected by natural seleciton?

• Merlot grapes

• Angora rabbits

• Influenza

• Poodles

Driving Forces of Evolution

In nature, it is not likely that all conditions for the H-W equilibrium will be met because POPULATIONS EVOLVE!

​

Allele/genotype frequency changes due to mutations and nonrandom mating are minor, therefore, there are 3 MAJOR mechanisms of evolution:

1. Natural Selection

2. Genetic Drift

3. Gene Flow​

Multiple Select

Which of the following are driving mechanisms of evolution? Select all that apply.

• sexual selection

• natural selection

• genetic drift

• gene flow

Sexual Selection

Certain individuals are more likely to obtain mates.

• Sexual dimorphism: differences between two sexes (size, color, ornamentation, behavior)​​

  ​

• Intersexual selection: mate choice (individuals of one sex, usually females, are choosy in selecting their mates from another sex

• Intrasexual selection: competition with the same sex

​

​

Sexual selection may lead to pronounced secondary differences between the sexes.

Natural Selection

The only evolutionary mechanism that continually leads to adaptive evolution.

​

Relative fitness: contribution an individual makes to the gene pool of the next generation relative to the contribution of others

​

Natural selection can occur in 3 ways:

1. directional selection

2. disruptive selection

3. stabilizing selection​

Natural selection CANNOT fashion perfect organisms. Selection can only edit existing variations. Evolution is limited by historical constraints. Adaptations are often compromises. Chance, natural selection, and the environment interact.

Multiple Choice

A population of giraffes lives in a forest with trees of varying heights. Following a flood in the area, all shorter plants were destroyed and only tall trees remain. After many generations, it is noted that giraffes living in this forest have longer necks, on average, than giraffes living in the same forest prior to the flood. 

What type of selection has occurred?

• destabilizing selection

• disruptive selection

• directional selection

• stabilizing selection

Genetic Drift

Genetic Drift: unpredictable fluctuation of alleles from one generation to the next

• Significant genetic drift in small populations

• Allele frequencies change at random

• Can lose genetic genetic variation in populations

• Can cause harmful alleles to become fixed

​

Types: founder effect and bottleneck effect​

Amoeba Sisters: Genetic Drift​

Multiple Choice

Genetic drift is change in the allele frequency of a population due to...

• random chance

• natural selection

• non-random mating (sexual selection)

• artificial selection

Gene Flow

Gene Flow: population gains and losses due to immigration or emigration

Gene Flow Video

Multiple Choice

Which of the following is true?

• Gene pool frequencies do not change as a result of migration in or out of a population.

• Gene flow occurs only as a result of isolation of a small population.

• Gene flow can cause new alleles to enter a population's gene pool.

• Gene flow is due the the selection of the most favorable traits.