BIOL Ch. 14 - Non adaptive Evolution and Seiiation

a. Will a change in allele frequencies always result in a beneficial evolutionary change for the population?

A change in allele frequencies does not mean that a beneficial evolutionary change has happened. There may be shifts in allele frequencies that are neither beneficial nor harmful.

a. What is a gene pool?

A gene pool is the collection of alleles in a particular population.

FOUNDER EFFECT

A type of genetic drift in which a small number of individuals leaves one population and establishes a new population, resulting in lower genetic diversity than in the original population

BOTTLENECK EFFECT

A type of genetic drift that occurs when a population is suddenly reduced to a small number of individuals, and as a result alleles are lost from the populations

1. What do genetic drift, gene flow, and mutation all have in common? A. chance B. changes in the DNA of alleles C. a decrease in allele frequency D. can only happen to small populations of individuals

A. chance

1. What was different among the populations of white-footed mice in Manhattan? A. species name B. gene pools C. food sources D. predators

A. gene pools

1. What would help a population with inbreeding depression? (Choose all that apply.) A. antidepressants B. mutation C. gene flow D. a selective pressure

A. mutation B. gene flow

1. The common characteristic of the variety of ways in which species maintain reproductive isolation is: A. offspring that resemble only the mother. B. offspring that resemble only the father. C. no offspring are viable. D. no offspring are able to reproduce themselves.

A. no offspring are able to reproduce themselves.

1. Speciation occurs when: A. two populations are geographically separated. B. two populations look distinctly different. C. two populations are no longer able to interbreed to produce fertile offspring. D. two populations utilize different food sources.

A. two populations are no longer able to interbreed to produce fertile offspring.

a. Can you swim in a gene pool?

Actually, you could if you extracted all the DNA from a population—although it would be pretty viscous...

NONADAPTIVE EVOLUTION

Any change in allele frequency that does not by itself lead a population to become more adapted to its environment; the mechanisms of nonadaptive evolution are mutation, genetic drift, and gene flow

a. Based on this definition, why do scientists say that all populations undergo some measure of genetic drift?

Because all populations are affected by chance.

1. A population of viruses has an error-prone RNA polymerase.

Because an error-prone RNA polymerase introduces mutations into the mRNA, the likely evolutionary mechanism for this population of viruses is mutation.

1. True or False: Evolution can occur without a change in allele frequency.

False

1. True or False: If a mutation happens to a specific allele in an individual organism, evolution has occurred.

False

1. True or False: Most natural populations are in Hardy-Weinberg equilibrium.

False

a. For evolution to occur, what must happen to a population's gene pool?

For evolution to occur, the frequency of alleles in a population's gene pool must change.

1. Two populations of hermit crab live in the same lagoon.

Gene flow is likely to happen because the two populations are close enough to mate and reproduce with each other.

How can genetic diversity be increased in populations, and why is more diversity beneficial?

Genetic diversity can be increased in populations by gene flow. Gene flow results when individuals move from one population to another or mate with individuals from a different population, introducing new alleles to the receiving population. Increased genetic diversity is beneficial because the population is more likely to survive a selective or random event if it has many varieties of alleles and thus many phenotypes of individuals. For example, a virus that infects and kills individuals with a specific allele would cause more damage to a population most of whom had that allele than to a population whose gene pool was more varied.

a. What is genetic drift?

Genetic drift is the change in allele frequencies from one generation to the next purely as a result of chance.

1. A volcanic eruption kills most of a certain species of beetle.

Genetic drift, specifically the bottleneck effect, because the population of beetles is reduced to a few members.

1. A few polar bears are separated from their population by a random ice drift. Consider this new smaller population.

Genetic drift, specifically the founder effect, because a few individuals separated from the main population will now start a new one.

INBREEDING

Mating between closely related individuals. Inbreeding does not change the allele frequency within a population, but it does increase the proportion of homozygous individuals to heterozygotes.

REPRODUCTIVE ISOLATION

Mechanisms that prevent (and therefore gene flow) between members of different species.

1. A disease ravishes a population of wild corn.

Natural selection, because the disease will kill any susceptible plants and leave those with alleles providing disease resistance.

Can a natural population ever be in Hardy-Weinberg equilibrium?

No, a natural population can never be in Hardy-Weinberg equilibrium because no population found in nature will ever have all of these conditions. There will never be an infinitely large population with no mutation, no mating preference, and no natural selection. At a given time, it is possible that one or more of these conditions would apply to a natural population, but this population will change, and at no point would all of the conditions apply to a natural population.

Why does inbreeding have negative consequences for populations?

Populations with high levels of inbreeding have low levels of genetic diversity due to a lack of gene flow. In extreme cases, deleterious alleles can accumulate in the population resulting in a population poorly adapted for its environment.

GENETIC DRIFT

Random changes in the allele frequencies of a population between generations; genetic drift tends to have more dramatic effects in smaller populations than in larger ones

Describe the biological species concept.

The biological species concept states that species are groups of organisms that are reproductively isolated from other groups of organisms. This means that members of different species cannot mate and produce fertile offspring.

BIOLOGICAL SPECIES CONCEPT

The definition of a species as a population whose members can interbreed to produce fertile offspring

a. Why does genetic drift affect smaller populations more dramatically than larger ones?

The effects of genetic drift are more severe for smaller populations because smaller populations are typically less genetically diverse. If you start with a homogeneous population and have a drift event, either a founder effect or a bottleneck effect, the population is likely to have even less diversity after the drift. A population that does not have much genetic diversity may not be able to survive future events or selection pressures as well, if at all, as a genetically diverse population.

List and describe the five conditions required for a theoretical population to be in Hardy-Weinberg equilibrium.

The five conditions necessary for a population to be in Hardy-Weinberg equilibrium: 1. No mutations occur: new alleles are not introduced into the population. 2. No natural selection occurs: no selective pressure changes the allele frequency. 3. The population is infinitely large (no genetic drift): the population cannot be reduced to yield a lower genetic diversity. 4. No gene flow: new alleles are not introduced into the population. 5. Mating between individuals is random: there is no selective pressure favoring mating between individuals and thus no favor for specific alleles over others.

SPECIATION

The genetic divergence of populations, leading over time to reproductive isolation and the formation of new species

GENE FLOW

The movement of alleles from one population to another, which may increase the genetic diversity of a population

INBREEDING DEPRESSION

The negative reproductive consequences for a population associated with having a high frequency of homozygous individuals possessing harmful recessive alleles.

HARDY-WEINBERG PRINCIPLE

The principle that, in a nonevolving population, both allele and genotype frequencies remain constant from one generation to the next

ALLELE FREQUENCY

The relative proportion of an allele in a population

POPULATION GENETICS

The study of the genetic makeup of populations and how the genetic composition of a population changes

GENE POOL

The total collection of alleles in a population

a. What are two major mechanisms of genetic drift?

The two mechanisms of genetic drift are the founder effect and the bottleneck effect.

a. How are the founder effect and bottleneck effect similar? How are they different?

They are similar in that a genetically diverse starting population becomes less diverse after drift. In each case, a few individuals end up starting a new population. They are also the same in that they are random and nonadaptive. The founder effect and bottleneck effect describe different mechanisms of genetic drift. A founder effect happens when a few individuals migrate to found a new population, leaving the original population reasonably unchanged, whereas a bottleneck effect is the result of eliminating a large portion of the original population, leaving a few individuals to rebuild the population.

1. True or False: A population with a large gene pool is more genetically diverse than a population with a small gene pool.

True

1. True or False: You can apply the Hardy-Weinberg equation to a population that is not in equilibrium.

True

a. Can different populations of the same organism have different gene pools? Why or why not?

Yes, different populations of the same organism can have different gene pools. Different populations of the same organism can be under different selection pressures depending on a variety of conditions. Physical location, for example, may cause differing allele frequencies between the two populations.