[LS 7B] week 4

what mechanism of evolution lead to adaptation

*only natural selection*

adaptation

- confers fitness - has a history of selection for that trait (traits that appear in today gen) - form indicates function -> adaptation can become traps in changing world

mechanism of evolution

1) natural selection -> change both allele and genotype frequency 2) mutation -> mutation is a rare event. This means that it is generally not important as an evolutionary mechanism that leads allele frequencies to change 3) migration 4) non-random mating: the genotype frequencies change, whereas the allele frequencies do not 5) genetic drift

drawback of using observable trait to measure variation

1. traits can be encoded by many genes 2. phenotype are both product of genotype n environment

Two alleles of a given gene exist in a population: CTGT and TGTC. (Note: The codes given are only for the transcribed strand of the DNA in the two alleles.) Three possible single crossover events are possible between these two alleles. As a result of the three different crossover events, how many total new alleles (new sequences of DNA) could be produced?

6 công thức: 2n

The fur color in a colony of mice has been brown for many generations. One gene appears to code for the fur color pigment. In a recent litter of mouse pups, one mouse was born with white fur. Which of the following could have caused this change in fur color? A., a mutation in the DNA sequence of the gene for brown fur Choice B., recombination between genes for fur color Choice C., All of these choices are correct.

A C is wrong because only 1 gene code for fur color recombinatn only mix allele combination, not making new alleles ex: all white fur black eye -> white fur blue eye

whether or not a population is in Hardy-Weinberg equilibrium?

A large breeding population. Random mating. No change in allelic frequency due to mutation. No immigration or emigration. No natural selection.

Darwins posulates in modern synthesis

As a result of mutation creating new alleles, and segregation and independent assortment shuffling alleles into new combinations, individuals within populations are variable for nearly all traits Individuals pass their alleles on to their offspring. In most generations, more offspring are produced than can survive Individuals that survive and reproduce, or who reproduce the most, are those with alleles and allelic combinations that best adapt them to their environment.

Darwin did not know how traits were inherited

Believed in blending inheritance Individual traits would be lost by merging with other traits After Mendel was re-discovered we know that alleles are inherited independently

what is evolution

Change in allele *or* genotype frequencies in a population over time

what is genetic rift?

Genetic drift is a mechanism of evolution in which allele frequencies of a population change over generations due to chance (sampling error or disappearance of particular genes as individuals die or do not reproduce.) => a beneficial allele may be lost, or a slightly harmful allele may become fixed, purely by chance

Why is natural selection more effective in a large versus small population?

In small, reproductively isolated populations, unique circumstances exist that can produce unexpected or rapid changes in gene frequencies. These changes are totally independent of mutation and natural selection. These changes are due solely to chance factors. The smaller the population, the more susceptible it is to such random changes. (genetic drift)

how does natural selection affect an individual?

It is the individual that lives or dies, reproduces, or fails to reproduce. Traits that are disadvantageous to the individual are therefore selected against by natural selection, even if they are beneficial to the species as a whole.

Why is it thought that the majority of natural selection is stabilizing selection? a. Mutations produce extreme phenotypes, which are selected for. b. Most mutations are beneficial and produce intermediate phenotypes. c. Directional selection is more common because it increases adaptations to the environment. d. Most mutations are deleterious and produce an extreme phenotype that is selected against. e. Artificial selection is the most common, which is a type of stabilizing selection.

Most mutations are deleterious and produce an extreme phentoype that is selected against.

Natural selection is nonrandom, but not progressive

Natural selection increases adaptation but is not directional We see trend to increased complexity but some organisms decrease in complexity Tapeworm Snake

how does non-random mating cause evolution?

Neither random nor non-random mating will influence the amount of genetic variation in a population on their own, they only change how genes are distributed into genotypes. If you have random mating and no other evolutionary forces (e.g., no selection), genotype frequencies in your population will not change. Non-random mating can change the genotype frequencies in a population, even in the absence of any other evolutionary forces.

Darwin's theory

Observation 1: All populations have the ability to grow exponentially • Observation 2: Limited resources prevent populations from growing exponentially • Observation 3: Variation exists within a population • Observation 4: This variation must be heritable

Natural selection acts on individuals, not groups

Organisms are never self-sacrificing or altruistic Only endanger themselves for selfish gain Prairie dog alarm calls Lions nursing other cubs Do so because of relatedness or reciprocity Group selection does not exist

what evolve?

Populations evolve, not individuals. But natural selection acts on individuals, not ppltn

Meerkats are small desert mammals that live in groups of 20-50 individuals. You observe one meerkat standing upright on a stump, looking around, while other meerkats forage for food. You hypothesize that this is an example of kin selection. What additional information would you need to know to evaluate your hypothesis? the degree of genetic relatedness of this meerkat to all members of the group the gender of this meerkat as well as that of all other members of the group all other activities of this meerkat as well as those of all other members of the group the foraging success of this meerkat as well as that of all other members of the group the body size of this meerkat relative to other members of the group

a

The goldenrod gall fly lays its eggs on the terminal buds of goldenrod plants. Larvae chew through the buds and into the stems, where their saliva induces the plant to generate a gall, or outgrowth of tissue that then provides food and shelter for the developing larva. The larvae are prey to both parasitoid wasps and to birds; wasps selectively prey on larvae inside the smallest galls while birds selectively prey on larvae inside the largest galls. Goldenrod gall flies are therefore subject to _____ selection. stabilizing directional disruptional heterozygote balancing

a

Why are mutation and recombination the only processes that can increase genetic variation? a. Whey are the only processes that can produce new genotypes. b. They are the only processes that changes allele frequency. c. They are the only processes that can produce deleterious results. d. They are the only processes that is not random. e. They are the only processes that cannot be influenced by artificial selection.

a

Why does genetic drift have more of an impact on the evolution of small populations than large ones? Sampling from generation to generation is more variable in small populations than large. Small populations are affected more by stabilizing selection. Small populations are less affected by mutations. Small populations have greater rates of mutation. Small populations are more prone to migration.

a

artificial selection is a. directional b. stabilizing c. disruptive

a

Which type of selection increases overall genetic variation in a population? a. disruptive selection b. directional selection c. stabilizing selection

a -> lead to the idea of speciation

Why can't we measure genetic variation in a population using observable traits (phenotypes)? (Select all that apply.) Many traits are encoded by multiple genes. All traits are encoded by a single gene. Phenotypes are not determined by genes. The environment can also affect the phenotype.

a d

exaptation

a trait that was shaped for a different function but takes on a dif use

what kind of mutation result in adaptation?

advantageous Advantageous mutations can increase in frequency in a population until eventually they are carried by every member of a species. -> fixed alleles

evidence of evolution

any change in allele frequencies, genotype frequencies, or both constitutes evolution.

sign of evolution

any change in frequency of genotype or allele

Females of a species of parasitic wasps locate their prey, a leaf-eating caterpillar, by hunting for it visually. One year, one female appeared in the wasp population with the ability to locate the prey by smell. The most likely place of occurrence of the mutation causing this change was: A., in the DNA in one of the egg cells in the individual with the new phenotype. Choice B., in the DNA in the egg cell that developed into the individual with the new phenotype. Choice C., in the DNA of one of the olfactory (smell) receptor cells on one antenna of the individual with the new phenotype. Choice D., in the DNA of the cells in the wasp's eye.

b

Individuals that are heterozygous for sickle-cell anemia are more resistant to malaria than those that do not have a sickle-cell allele. Why does the sickle-cell allele not become fixed in the population? a. Individuals that are homozygous without the sickle-cell allele produce more offspring than those with the sickle-cell allele. b. Individuals that are homozygous for the sickle-cell allele have sickle-cell anemia, and are at a fitness disadvantage. c. Individuals homozygous for the sickle-cell allele do not have the same resistance to malaria. d. Individuals heterozygous for the sickle-cell allele die earlier than either of the homozygous individuals. e. Analysis indicates the allele is becoming fixed in the population.

b

What is the hypothetical long-term result of different mutations accumulating in different populations? a. the extinction of one population b. the evolution of different species c. merging the populations through migration d. fixation of the same alleles in both populations e. decreased genetic isolation

b

Which type of selection change the mean? a. disruptive selection b. directional selection c. stabilizing selection

b

Which of the following is an example of stabilizing selection? antibiotic resistance in bacteria selection for average birth weight in humans decrease in the number of birds with intermediate-sized beaks who are unable to eat large or small seeds breeding dogs from wolves

b what is a and d

According to William Hamilton's formulation of kin selection, in which scenario would you have the greatest fitness? Sacrificing yourself for the benefit of one child. Sacrificing yourself for the benefit of two nieces and/or nephews. Sacrificing yourself for the benefit of three nieces and/or nephews. Sacrificing yourself for the benefit of one sibling.

c

Prior to the publication of Darwin's On the Origin of Species, people thought what about species? Species evolved at one point, but no longer changed because they were not adapted to their environment. Species changed over time as guided by a divine creator. Species were designed already perfectly adapted to their environment. Species changed over time because they were not adapted to their environment.

c

Which of the following reflects a difference in fitness among individuals in a population? a. All individuals in the population have the same number of offspring. b. Males in the population all sire equal numbers of offspring. c. All offspring born in the population come from 25 percent of the females in the population. d. Males in the population have large horns on their heads to attract females.

c

Which one of the following statements does not describe intersexual selection? a. The female peacock's preference for their mates to have the showiest tail has promoted a rather large investment by the male into tail plumage. b. Males compete for the attention of the female with bright colors of advertisement displays. c. Physical traits such as large horns or other weaponry allow the males to win more fights with other males, hold larger territories, and have access to more females. d. Females choose their mates.

c

Which type of selection decreases overall genetic variation in a population? a. disruptive selection b. directional selection c. stabilizing selection

c

Dodos were flightless birds that have been extinct for about 300 years. Imagine that biologists found two surviving dodos on present-day Earth and mated this pair of birds. What would you expect of the resulting dodo population? a. Mutation rate in dodo population could increase, given the small population size. b. The maximum number of alleles present for any gene in the new population is two. c. Adaptations will occur in this population as a result of genetic drift. d. Due to a population bottleneck, the frequency of alleles in this new dodo population may be very different from the frequencies expected in larger (now non-existent) populations.

d

Due to hunting, the population of Northern elephant seals was reduced to 20 individuals at the end of the 19th century. Since then, their population has since rebounded to over 30,000. What is the most likely long-term effect of hunting on the elephant seal population? A The population has allele frequencies similar to those in the original population. B The population contains high allelic diversity. C The population is more likely to survive disease. D Individuals are genetically similar to each other.

d

Endangered species with very small populations are especially at risk of loss of genetic diversity due to: natural selection. immigration. mutation. genetic drift.

d

Genetic variation has two sources-mutation and: genetic drift. natural selection. non-random mating. recombination. cell division.

d

Group selection is not typically seen as an evolutionarily stable strategy because: None of the answer options is correct. it cannot explain behaviors for species with solitary individuals. average relatedness is very low between individuals in a population, therefore individual fitness cannot increase. selfish behaviors are more likely to increase individual fitness.

d

Why is it thought that the majority of natural selection is stabilizing selection? Mutations produce extreme phenotypes, which are selected for. Artificial selection is the most common, which is a type of stabilizing selection. Most mutations are beneficial and produce intermediate phenotypes. Most mutations are deleterious and produce an extreme phenotype that is selected against. Directional selection is more common because it increases adaptations to the environment.

d

most mutations are

deleterious -> extreme phenotype -> nat selectn is stabilizing

Sexual selection tends to cause bigger size, more elaborate weaponry, or brighter colors in males. Is this an example of stabilizing, directional, or disruptive selection?

directional

Migration reduces genetic differences between populations by allowing gene _____ between the two. augmentation deletion repression drift flow

e

Migration, genetic drift, and mutation are like natural selection in that they: a. are all methods of evolutionary change. b. result in evolution of a population. c. may alter the genotype frequency in a population. d. may alter the allele frequency in a population. e. all of these choices are correct.

e

What is the result of a mutation that occurs in somatic cells? There will never be any visible effect. The mutation will be deleterious. The mutation will be passed along to the organism's offspring. The mutation will prevent all reproduction. The mutation may be expressed in the individual, but will not be passed along to its offspring.

e

s a population geneticist, you find a species of snails with more genetic diversity than humans. What does this mean? The snails have more genes on their chromosomes than humans. There is not enough information provided to answer this question. The snails have more mutations occurring than humans. The snails have more DNA than humans. There is more variety in the gene pool of snails than humans.

e c is wrong because not all mutations remain in the ppltn *most* deleterious mutations are wiped out *some* remain due to genetic drift

Malthus pointed out that populations have the potential to increase geometrically. What did this observation suggest that contributed to the idea of natural selection? Populations may grow faster than other competing populations. Populations may grow quickly and spread out over the planet. Populations grow quickly, but predators grow more quickly. Populations may grow quickly, and then will evolve more quickly. Populations may grow faster than their resources.

e d wrong because growing quickly does not necessarily mean it will evolve quickly grow: expand in size threshold in resource -> survival of the fittest

which mechanism of evolution can change both allele and genotype frequency?

everything except non-random mating

Hardy-Weinberg equilibrium

evolution does not occur allele and genotype f does not change

Consider a population of killer whales. The gene pool of this population would only contain alleles harboring beneficial or neutral mutations, as deleterious mutations are efficiently eliminated from the gene pool of a species. True False

f

Traits favored by sexual selection are the same traits favored by natural selection. False True

f sexual selection does not necessarily result in adaptive trait

If a population has low genetic variation, it is more susceptible to drift

false drift tends to reduce genetic variation-the extent to which it does this depends on ppltn size (drift has a stronger effect on smaller ppltn), not on the existing amount of variation

natural selection itself is a stronger force in large ppltn than in small ppltn

false natural selection is often *more effective* in large ppltn because beneficial alleles are less likely to be lost due to drift, but the *strength* of selection is not dependent upon ppltn size

natural selection

filtering process that acts against deleterious alleles and in favor of advantageous ones -> *the only evolution mechanism that bring about adaptation*

factor that decreases genetic variation

genetic drift natural selection non-random mating migration (gene flow)

where and when are observed traits evolve

if it evolves from natural selection - variation - heritable - differential reproductive success not all traits observed are adaptation (result of natural selection) might be traits that are carried w adaptative trait

how could mendel's discrete traits account for the continuous variation seen in natural population?

instead of a single gene contributing to a trait, there could be several gene contribute to the trait => extending Mendel theory to include multiple genes per trait account for pattern of continuous variation

traits that are subjected to natural selection

most are continuous trait w normal distribution ex: cheetah speed -> there will be some that run faster n slower than the distribution mean

factor that increases genetic variation

mutation

ultimate source of genetic variation

mutation

which mutation increase genetic variation?

mutation

why isnt mutation not as important as other evolutionary mechanism?

mutation is a rare event. This means that it is generally not important as an evolutionary mechanism that leads allele frequencies to change. However, as we have also seen, it is the source of new alleles and the raw material on which the other forces act. Without mutation, there would be no genetic variation and no evolution.

source of genetic variation

mutations and recombination Mutation generates new variation, and recombination shuffles mutations to create new combinations.

unit of evolution

natural selection --> individual populatn and species *evolve* (its the frequency of alleles of population as a whole that change -> evolution)

Some proteins have a slower molecular clock due to _____ selection, which eliminated harmful alleles. a. neutral b. negative c. positive d. disruptive e. beneficial

negative

does populations get larger at an ever-increasing rate?

no because the resources upon which populations are dependent—food, water, places to live—are limited

does whether a trait is dominant or recessive affect the changing of its frequency?

no dominant wont mean it will spread over the whole population or recessive wont die out

does somatic mutations add to genetic variation?

no only germ-line mutations can change an allele and that new allele has to be inherited by offspring of the individual where the mutation first occurred

does directional selection continue infinitely in one direction?

no due to 1) environmental change -> envr resources go back to its initial state 2) a given trait will eventually reach a point where it cant get any bigger or smaller

does het frequency <=50%

only in HW equilibrium

gene flow (migration)

reduce genetic differences -> might cause a decrease in a ppltn's fitness

what are the primary mechanism for evolution?

selection, migration, mutation, genetic drift, or non-random mating

significant of mutation

source of new alleles and the raw material on which the other forces act. Without mutation, there would be no genetic variation and no evolution.

fitness

success in surviving and leaving progeny the extent to which the individual's genotype is represented in the next generation

All mutations in a population—both harmful and beneficial—contribute to the evolution of that population. a. true b. false

t

If B = the benefit of a behavior to a recipient, C = the cost of the behavior of the donor, and r = the degree of relatedness between the recipient and donor, then if rB > C, altruism can evolve. True False

t

Mutation increases genetic variation. False True

t

interplay between natural and sexual selection

threshold for a trait that is reproductively favorable

Genetic drift can occur in the absence of ppltn bottlenecks or founder effect

true

In a given population, all humans have the same blood type O. If no other alleles for blood type exist in this population, this population is "fixed" for the O allele. False True

true

It is possible for large popultn to have low genetic variation

true while low genetic variation in a large ppltn suggests that ppltn experienced a bottleneck in the past, that reduced variation often remains after ppltn size has recovered

can evolution occur w/o allele changing?

y ex: the A/G allele frequencies stay the same from one generation to the next, the frequencies of the different genotypes (that is, of AA, AG, and GG) may change