BIO microevolution LOs
in a population there are 2 alleles of the R gene (R! and R2). genotypes of the R gene are found at the following frequencies: R1R1 = 0.54, R1R2=0.38, R2R2=0.08. what are the respective frequencies of the R1 and R2 alleles?
0.73, 0.27
In a gene pool of a population with 132 individuals, a fixed allele for a particular genetic locus has a frequency of
1
16% of a population is unable to taste the chemical PTC. these non-tasters are recessive for the tasting gene. 1. percentage of individuals in the population that are tasters 2. frequency of dominant and recessive allele 3. percentage of population that are heterozygous for the trait
1. 84 tasters 2. dominant 0.6, recessive 0.4 3. 48%
a population of mice is at HWE for a gene locus that controls for fur colour. the locus has 2 alleles, M and m. 70% of the gametes in the population have M allele. whats the percentage of mice are heterozygous?
42% = 2(0.7)(0.3)
64% of the inhabitants of a remote mountain village can taste PTC and they must have at least one copy of the PTC taster allele to show this dominant phenotype. if this pop conforms to HW expectations for this gene, what percentage must be heterozygous?
48%
A population of chimps is in HWE (Hardy-Weinberg equilibrium) for a gene that controls the presence or absence of an extra digit on their forelimbs. This gene has two alleles (D1 and D2), and 40% of the gametes in the chimp population carry the D1 allele. Given this information, what is the percentage of chimps that carry both the D1 and D2 alleles?
48%
Calculating phenotype frequencies: In a population that is in HWE, there are two alleles of the A gene (A1 & A2). You know that the frequency of the A1 allele is 0.4. Calculate the frequency of the other allele. A2 = 0.6 If A2 encodes a phenotype that is dominant to A1, what proportion of the population will show the A2 phenotype?
A1 = p = 0.4 A2 = q = 0.6 p2 + 2pq + q2 = 1 (Homozygous Recessive) + (Heterozygous) + (Homozygous Dominant) = 1 p2 = (0.4)2 = 0.16 2pq = 2 * 0.4 * 0.6 = 0.48 q2 = (0.6)2 = 0.36 Since we know that A2 is dominant, the heterozygous (A2A1) and homozygous dominant (A2A2) populations will show the A2 phenotype. 0.48 + 0.36 = 0.84 84% of the population will show the A2 phenotype, assuming that no natural selection, gene flow, genetic drift, mutations, or non-random mating occurred.
Explain why trade offs and genetic and historical constraints prevent adaptations from being perfect
Adaptations are not perfect solutions to challenges posed by a particular environment because they are compromised by (1) the necessity of meeting many challenges at the same time (fitness trade off); (2) the lack of "perfect" alleles or presence of alleles that affect more than one trait (genetic constraints); (3) the necessity of selecting only pre-existing variation in traits (historical constraints)
D10. Discuss adaptations, explaining why: there are limits to adaptation; not all traits are adaptive; why adaptation is not 'universally good'; and how an organism's phenotype represents a compromise or trade-off between the adaptive value of multiple traits. Identify/provide an example of a fitness trade-off. [Comprehension, Application]
An adaptation is any heritable trait that increases the fitness of an individual with the trait, compared to individuals without the trait. Not all traits are adaptive, species have vestigial (nonadaptive) traits. Evolution by natural selection does not lead to "perfection", besides carrying an array of traits that have no function, the adaptations that organisms have are constrained in a variety of important ways. Adaptations are not universally good because they are compromised by (1) the necessity of meeting many challenges at the same time (fitness trade off); (2) the lack of "perfect" alleles or presence of alleles that affect more than one trait (genetic constraints); (3) the necessity of selecting only pre-existing variation in traits (historical constraints). For example, in the Galapagos, medium ground finches with large bodies had an advantage because they won fights over food. but individuals with larger bodies require large amounts of food to maintain their mass, they tend to be slower and more prone to starvation. even if large size is advantageous, there's always an counteracting selection that prevents individuals from getting even bigger.
D10. Compare inbreeding and sexual selection, and their potential effects on a population; given a scenario, determine which is acting. [Comprehension, Application, Analysis] a. Explain how sexual selection has resulted in showy structures in males, commenting on what this indicates about the males (relating to fitness tradeoff, handicap hypothesis, honest signals, etc.); provide examples of male traits/behaviours to explain it. [Comprehension]
Because sexual selection tends to be much more intense in males and females, males tend to have many more traits that function only in courtship or male-male competition (in other words, sexually selected traits often differ sharply between the sexes). Sexually selected traits often differ sharply between the sexes; males often have exaggerated traits that they use in fighting or courtship. For example, male lions are larger than female lions and have an elaborate mane. For example, in swallows and many other species, its common to find that one cause of directional selection on a trait is counterbalanced by a different factor that causes selection in the opposite direction - which is a concept known as fitness trade-off.
D6.Describe the mechanism of evolution by natural selection, explaining why evolution is not progressive (i.e., moving towards 'perfection'), how natural selection is non-random and results in adaptations. [Comprehension] a. Describe how natural selection acts on phenotypic variation to alter the genetic structure of a population. [Comprehension]
Evolution by natural selection favours individuals that are well-adapted to their environment, that doesn't necessarily mean those individuals among populations that are bigger and stronger - just those who are better adapted. Evolution is not goal-directed or progressive (doesn't lead to perfection) besides carrying an array of traits that have no function (vestigial traits) all adaptations are constrained by trade offs, genetic and historical factors. Natural selection occurs when individuals with certain phenotypes produce more offspring than those without those phenotypes - its non-random. If certain alleles are favoured, it increases in frequency, while other alleles decrease in frequency - resulting in evolution.
D5. Differentiate between the different types of evolutionary mechanisms; the conditions under which they occur; their effects on a population's genetic structure (e.g., variation, and mean character value); their relative effects on evolution; and factors that can impact their effects. Given a scenario, determine the type(s) of mechanism(s) acting, and predict the effects on the population, justifying your choices. [Knowledge, Comprehension, Application, Analysis] d. Compare founder and population bottleneck events (causes and outcomes). [Comprehension]
Founder effect is a change in allele frequencies that occurs when a new population is established from a small group of individuals due to sampling error (i.e. small group is not a representative sample of the source population). A genetic bottleneck is a sudden reduction in the number of alleles in a population due to random events; causes allele frequencies to drift up and down randomly over time, and eventually can lead to the fixation or loss of alleles.
D5. Differentiate between the different types of evolutionary mechanisms; the conditions under which they occur; their effects on a population's genetic structure (e.g., variation, and mean character value); their relative effects on evolution; and factors that can impact their effects. Given a scenario, determine the type(s) of mechanism(s) acting, and predict the effects on the population, justifying your choices. [Knowledge, Comprehension, Application, Analysis] a. Compare gene flow and the founder effect (causes and outcomes). [Comprehension]
Founder effect is a change in allele frequencies that occurs when a new population is established from a small group of individuals due to sampling error (i.e. small group is not a representative sample of the source population). Gene flow is the movement of alleles between populations; occurs when individuals leave one population, join another and breed. Gene flow homogenizes allele frequencies among populations and can serve as an important source of new alleles.
D11. Relate and justify characteristics of an organism to their suitability as model organisms in evolutionary studies. [Comprehension, Analysis] - FRUIT FLIES
Fruit flies are good model organisms for evolutionary studies because they're inexpensive, their reproductive cycle is 2 weeks - so biologists don't have to wait very long to see results of evolutionary change; they produce lots of offspring - which will be good to see if there's a chance that mutations can arise.
D5. Differentiate between the different types of evolutionary mechanisms; the conditions under which they occur; their effects on a population's genetic structure (e.g., variation, and mean character value); their relative effects on evolution; and factors that can impact their effects. Given a scenario, determine the type(s) of mechanism(s) acting, and predict the effects on the population, justifying your choices. [Knowledge, Comprehension, Application, Analysis] b. Describe the impact of gene flow between two populations. [Comprehension]
Gene flow increases the similarity of allele frequencies in the source population and the recipient population. when alleles move from one population to another, the populations tend to be more alike.
D5. Differentiate between the different types of evolutionary mechanisms; the conditions under which they occur; their effects on a population's genetic structure (e.g., variation, and mean character value); their relative effects on evolution; and factors that can impact their effects. Given a scenario, determine the type(s) of mechanism(s) acting, and predict the effects on the population, justifying your choices. [Knowledge, Comprehension, Application, Analysis] c. Relate and explain the effects of drift as a function of population size; relate these effects to conservation biology. [Comprehension]
Genetic drift is most pronounced in small populations. The importance of drift in small populations is a particular concern for conservation biologists, because many populations are being drastically reduced in size by habitat destruction and other human activities. Small populations that occupy nature reserves or zoos are particularly susceptible to genetic drift. If drift leads to a loss of genetic diversity, which would impact endangered species.
D2.Justify the importance of genetic variation in populations to the process of evolution, explaining the ways in which variation is generated. Given a scenario/graph, classify: the degree of variation for that character; variation as qualitative or quantitative; and reasons for the variation (genetic, environmental, or both). [Comprehension, Application, Analysis]
Genetic variation says that (1) the number and relative frequency of alleles present in a particular population, (2) the proportion of phenotypic variation in a trait that is due to genetic rather than environmental influences in a certain population in a certain environment.
this is what defines what genotype frequencies should be if evolutionary mechanisms are not occurring
HWP
D4.Explain how the Hardy-Weinberg (HW) principle acts as a null hypothesis/model for evolution, relating the assumptions/conditions of HW to the mechanisms of evolution, and populations to which HW is applicable. [Comprehension]
HWP acts as a null hypothesis. Given a set of allele frequencies, HWP predicts what genotype frequencies will be when natural selection, mutation, genetic drift and gene flow are not affecting the gene; and when mating is random with respect to that gene.
Who has greater fitness: a world-class bodybuilder with a single child, or an overweight, middle-aged accountant with four children? Explain your answer.
If fitness is the ability of an individual to produce viable offspring relative to others of the same species, then I think that the middle-aged accountant with four children would have greater fitness - because this person produced the most offspring compared to the world-class bodybuilder with only one child.
D10. Compare inbreeding and sexual selection, and their potential effects on a population; given a scenario, determine which is acting. [Comprehension, Application, Analysis] a. Describe the phenomena of assortative mating (positive and negative) and its potential impact on a population. [Comprehension, Analysis]
In positive assortment, individuals choose mates that share a particular phenotypic trait with them, whereas, in negative, individuals choose maters that differ in a specific phenotypic trait. assortative mating is a nonrandom process, that brings about no evolutionary change because they change genotype frequencies not allele frequencies.
D10. Compare inbreeding and sexual selection, and their potential effects on a population; given a scenario, determine which is acting. [Comprehension, Application, Analysis] a. Describe the impact of inbreeding on a population's genetic variation, phenotypes, and heterozygosity; explain how non-random mating may not result in evolution. [Comprehension]
Inbreeding: A form of nonrandom mating; Changes genotype frequencies, leads to an increase in homzygosity and decrease in heterozygosity; Does not change allele frequencies, so it is not an evolutionary mechanism; These patterns can accelerate natural selection, can cause inbreeding depression (fitness declines due to deleterious recessive alleles that are homozygous). There are 2 fundamental points about inbreeding: 1. Inbreeding increase homozygosity; it takes alleles from heterozygotes and puts them into homozygotes 2. Inbreeding does not cause evolution, because allele frequencies do not change in the population as a whole
Is Intelligent Design scientific? Provide two reasons why Intelligent Design does OR does not fulfill scientific criteria.
Intelligent design is not scientific because (1) it cannot be observed (ID deals with the supernatural, which is outside the bounds of science) and (2) it cannot be tested (produces no predictions, cannot test hypotheses - ID has no predictive power)
D10. Compare inbreeding and sexual selection, and their potential effects on a population; given a scenario, determine which is acting. [Comprehension, Application, Analysis] a. Differentiate between inter- and intra-sexual selection; given a scenario, identify which is acting, which sex will show the greater variation in reproductive success, and the extent of sexual dimorphism, justifying your answer. [Comprehension, Application, Analysis]
Intrasexual refers to selection within a sex - often called male-male competition. Males will compete amongst one another for access to females. This can include stronger males killing or driving off the competition. Intersexual is between sexes - usually called mate or female choice. In this case, males compete against each other to be chosen by the females.
intrasexual and intersexual selection (differentiate between the two),
Intrasexual refers to selection within a sex - often called male-male competition. Males will compete amongst one another for access to females. This can include stronger males killing or driving off the competition. Intersexual is between sexes - usually called mate or female choice. In this case, males compete against each other to be chosen by the females.
D5. Differentiate between the different types of evolutionary mechanisms; the conditions under which they occur; their effects on a population's genetic structure (e.g., variation, and mean character value); their relative effects on evolution; and factors that can impact their effects. Given a scenario, determine the type(s) of mechanism(s) acting, and predict the effects on the population, justifying your choices. [Knowledge, Comprehension, Application, Analysis] a. Describe the random nature of mutations; how mutations are passed from one generation to next (vertically and horizontally); the role of mutation in evolution; and describe how a mutation in DNA has a wide range of possible evolutionary consequences. [Comprehension]
Mutation is an evolutionary mechanism that increases genetic diversity in populations, but despite this fact, mutation is random with respect to the affected allele's impact on the fitness of the individual. Mutations are passed from one generation to the next because errors and chromosome damage are inevitable, mutation constantly introduces new alleles into populations in every generation. Mutation's role in evolution is that if mutation did not occur, evolution would eventually stop - eventually there would be no variation for selection and drift to act on. How a mutation in DNA has a wide range of possible evolutionary consequences: most mutations in sequences that code for a functional protein or RNA result in deleterious alleles, which lower fitness and tend to be eliminated by purifying selection. there's also, beneficial alleles, that increases fitness, they should increase in frequency in the population due to natural selection.
Describing evolutionary processes: Some biologists encapsulate evolution by natural selection with the phrase "mutation proposes, selection disposes". Explain what they mean, using the formal terms you have learned to describe evolutionary processes.
Mutation produces new genetic variations, at random, without any forethought as to which variations might prove adaptive in the future. individuals with mutations are disadvantageous won't produce many offspring, but individuals with beneficial mutations will produce many offspring.
Why are mutations important in evolution, when most mutations are harmful?
Mutations are important because is it the only process that creates new alleles. If there were no mutations, evolution would eventually stop - there would be no variation for genetic drift and selection to act on. Even though most mutations are harmful, it's still the only process that has potential to create new beneficial alleles in a population.
D1.Provide arguments supporting evolution as a population process, explaining why individuals do not evolve. [Comprehension] (include example, HINT: TB)
Natural selection acts on individuals, because individuals experience differential reproductive success. But only populations evolve. Allele frequencies change in populations, not in individuals. For example, M. tuberculosis (TB) individuals with the mutant rpoB gene had higher fitness in an environment where rifampin (antibiotic) was present. The mutant allele producesa protein that's an adaptation when the cell's environment contains the antibiotic. This study confirmed that evolution by natural selection occurred, TB population evolved because the mutant rpoB allele increased in frequency.
D9. Describe various mechanisms by which natural selection does not lead to elimination of genetic variation. Given a scenario, determine/identify the process, justifying your choice. [Comprehension]
Natural selection: balancing selection - where multiple alleles are maintained in a species habitat range. this contains 3 mechanisms that does not lead to elimination of genetic variation, which are heterozygote advantage (where phenotype of heterozygotes has higher fitness than the phenotype of homozygotes), frequency dependent selection (where rare phenotypes have higher fitness than common phenotypes), and how fitness varies in time/space (where different phenotypes and alleles are favoured in different environments) .
Evolution: For what reasons might a fossil species in the Andes (South America) resemble one in the African mountains, even though they (the fossil species) are only distantly related? Explain.
One of the reasons for the resemblance is that both species came from a shared common ancestor, and after the continental drift the differences between the species became more pronounced, while some similarities remained. Another reason might be that since both species lived in mountainous areas, the features advantageous to living in the mountains were selected for, thus resulting in the similarities between species.
- qualitative and quantitative variation (differentiate between these terms)
Quantitative variation is variation typically involving multiple genes, e.g. human height, tail length in monkeys; Qualitative variation is variation typically involving one gene, e.g. flower colour (either purple or white), blood type A/B/AB
D10. Compare inbreeding and sexual selection, and their potential effects on a population; given a scenario, determine which is acting. [Comprehension, Application, Analysis] b. Explain the adaptive value of sexual cannibalism and self-sacrifice. [Comprehension, Analysis]
Redback spiders example - inter sexual selection. - Male spiders will find female and present himself during courtship and they may/may not mate. if they do mate, and if male does summersault - it says female can eat him (self-sacrifice). Males who allow females to consume parts of their body has more offspring than those who didn't - increase in the alleles for this behaviour in next generation. This is adaptive because the chances are low to meet a second female to mate with.
D7.Differentiate between the various types of selection (e.g., directional) and their effects (e.g., genetic variation, mean character value) on a population (either alone or in tandem) over a period of time. Given a scenario, determine the type(s) of selection acting and predict the effects on the population. [Knowledge, Comprehension, Application, Analysis]
Types of Natural Selection (Patterns of Natural Selection): Directional selection: favours one extreme phenotype with the result that the average phenotype of a population changes in one direction; genetically reduces overall genetic variation in a population. Disruptive selection: favours extreme phenotypes at both ends of the range of phenotypic variation; maintains overall genetic variation in a population. Stabilizing selection: favours phenotypes near the middle of the range of phenotypic variation; reduces overall genetic variation in a population. Sexual selection: favours individuals with traits that increase their ability to obtain mates; acts more strongly on males than females
artificial selection is likely to produce population-level changes most quickly in organisms with
a short generation time
Genetic drift a) explain why drift leads to random loss or fixation of alleles b) why drift is particularly important as an evolutionary force in small populations
a) when allele frequencies fluctuate randomly up and down, sooner or later the frequency of an allele will hit 0. that allele thus is lost from the population, and the other allele at that locus is fixed. b) in small populations, sampling error is large (e.g. accidental death of individuals would have large impact on allele frequencies)
a trait that improves the fitness of its bearer, compared with individuals without the trait
adaptation
any heritable trait that increases the fitness of an individual with that trait, compared with individuals without that trait, in a particular environment
adaptation
this is process by which organisms become better matched to their environment
adaptation
this s a genetically based trait that increases in an individual's ability to produce offspring in a particular environment.
adaptation
artificial selection was used on corn to produce a single strain of corn with increased growth rates and greater resistance to fungus, but farmers still select for these traits, the productivity of this strain is no longer increasing, which means that...
all or most of the natural variation for these traits is gone
The Hardy-Weinberg equation is useful for the calculation of changes in
allele freq
relative abundance of different alleles for a gene without a population
allele frequency
how can allele frequencies change under stabilizing selection, even the average phenotype in the population does not
alleles associate with extreme phenotypes are eliminated, alleles associated with intermediate phenotypes increase in frequency
mating that is nonrandom with respect to specific traits; if this is positive, individuals choose mates that share a particular phenotypic trait with them; f this is negative, individuals choose mates that differ in a specific phenotypic trait
assortative mating
this decreases proportion of heterozygotes
assortative mating
M. tuberculosis developed antibiotic resistance to rifampin because: a. rifampin induced mutations in the bacteria that allowed them to survive the rifampin b. the mutation arose because the bacteria needed to adapt (develop resistance) otherwise no bacteria would survive c. some bacteria had mutations that allowed them to survive
b
you have a mixed population in the lab. approximately half of them are susceptible to the antibiotic rifampin. the other half are not, due to a mutation in the rpoB gene. the probe mutation results in a RNA polymerase that doesn't work as well as the normal form, thus transcription is not as rapid, as these bacteria grow much more slowly than those with WT enzyme. if the population is maintained on media that lacks rifampin (environment without antibiotics) what is expected to occur over a period of time? a. rifampin resistant bacteria will increase in proportion compared to the rifampin susceptible bacteria b. rifampin susceptible bacteria will increase in proportion compared to the rifampin resistant bacteria c. rifampin susceptible bacteria and rifampin resistant bacteria will remain in approximately equal proportions
b
in a human population where HIV infection is common, there are several alleles at a gene that affects resistance to HIV infection. a new co-dominant allele A4 confers the highest resistance. suppose you genotype a large number of individuals in this population (after several generations). predict how observed genotype frequencies compare to those expected under HWP conditions a. because human populations are so large, genotypes will be in HW proportions b. there are 2 few A4 homozygotes c. there's an excess of genotypes containing A4 d. all alleles except A4 would be eliminated e. the frequency would be equal to p^2
c
a pattern of natural selection that favours one extreme phenotype with the result that the average phenotype of a population changes in one direction; generally reduces overall genetic variation in a population
directional selection
this tends to increase proportion of heterozygote neither allele frequencies
disassortative mating
a pattern of natural selection that favours the extreme phenotypes at both ends of the range of phenotypic variation; maintains overall genetic variation in a population
disruptive selection
t/f: inbreeding and assortative mating change allele frequencies but do not change genotype frequencies
f
T/f: Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.
f - tends to maintain genetic variation
the ability of an individual to produce viable offspring relative to others of the same species
fitness
a compromise between traits, in terms of how those traits perform in the environment),
fitness trade-off
identify the evolutionary mechanism: equalizes allele frequencies between populations
gene flow
the movement of alleles between populations occurs when individuals leave one population, join another, and breed
gene flow
Movement of alleles between populations is _____ and results in _____.
gene flow, decreased genetic differences between populations
all of the alleles of all of the genes in a certain population
gene pool
The northern elephant seal went through a severe population decline as a result of hunting in the late 1800s. The population has rebounded (i.e., has returned to higher numbers), but is now homozygous for nearly every gene studied. This is an example of
genetic drift
any change in allele frequencies in a population that is due to chance - it causes allele frequencies to drift up and down randomly over time; this occurs in every population and in every generation.
genetic drift
identify the evolutionary mechanism: causes random fluctuations in allele frequencies
genetic drift
this causes allele frequencies to drift up and down randomly
genetic drift
this says that (1) the number and relative frequency of alleles present in a particular population, (2) the proportion of phenotypic variation in a trait that is due to genetic rather than environmental influences in a certain population in a certain environment
genetic variation
percentage of individuals (relative abundance) in a population possessing each genotype for a given locus (gene)
genotypic frequency
if males can survive despite this trait (deleterious), allowing females to choose traits that are genuinely fit; if you can survive, and get that female, you're going to have a higher fitness
handicap hypothesis
what does this mean when an allele reaches "fixation"
has frequency of 1
M. tuberculosis: if the antibiotic rifampin were banned, would the mutant rpoB gene have lower or higher fitness in the new environment? would strains carrying the mutation continue to increase in frequency M. tuberculosis populations?
if rifampin were banned, its likely that rpoB mutant strains would have had lower fitness in the drug-free environment, since it produces an additional protein that's not adaptive in the absence of rifampin. the resistant strain would not continue to increase in frequency M. tuberculosis populations
mating between closely related individuals; increases homozygosity of a population and often leads to decline in the average fitness
inbreeding
in inbred offspring, fitness declines due to deleterious recessive alleles that are homozygous
inbreeding depression
whats the unit of natural selection
individuals
this refers to selection between sexes - usually called mate or female choice
intersexual selection
this refers to selection within a sex - often called male-male competition
intrasexual selection
In frequency-dependent selection, the highest mortality can be expected in which of the following?
most abundant phenotype
identify the evolutionary mechanism: introduces new alleles
mutation
the origin of genetic variation is
mutation
these are always random with respect to the needs of the organism
mutation
this is a change in an organism's DNA
mutation
mutation is the ultimate source of genetic variability. why is this statement correct?
mutation is the only source of new alleles
most of these are harmful, or neutral to the organism in which they occur
mutations
identify the evolutionary mechanism: only produces adaptation
natural selection
the process by which individuals with certain heritable traits tend to produce more surviving offspring than do individuals without those traits, often leading to a change in the genetic makeup of the population. Natural selection is a major mechanism of evolution
natural selection
what changes DNA that has no impact upon the phenotype of an individual
neutral
matings between individuals may not be random with respect to the gene in question; for example, in insects, vertebrates and other animals, females don't mate at random, but actively choose certain males; includes: inbreeding, assortative mating and sexual selection
nonrandom mating
The Hardy-Weinberg principle tells us what to expect when a sexually reproducing population is
not evolving
the delta-32 mutation, a recessive gene gives humans protection from the HIV infection. the allele frequency in a town in Sweden is 20%. 1. percentage of individuals in the population that have 2 copies of the gene and are immune to HIV 2. 1. percentage of individuals in the population that are less susceptible to the disease, since they are heterozygous
q=0.2, p=0.8 1. 0.2^2=0.04 2. 32%
directional selection can lead to the fixation of favoured alleles. when this occurs, genetic variation is zero and evolution stops. explain what mechanisms may act to reduce the likelihood of such fixation
selective pressures often change over time or in different areas occupied by the same species. even if selective pressures do not vary, mutation continually introduces new alleles
any trait that differs between males and females
sexual dimorphism
a pattern of natural selection that favours the individuals with traits that increase their ability to obtain mates; acts more strongly on males than females
sexual selection
a pattern of natural selection that favours individuals with traits that increase their ability to obtain mates; acts more strongly on males than females
sexual selection (nonrandom mating)
If a storm kills many small birds in a population, but only a few medium- and large-sized ones, which type of selection is likely operating?
stabilizing
a pattern of natural selection that favours phenotypes near the middle of the range of phenotypic variation
stabilizing selection
t/f: inbreeding and assortative mating change genotype frequencies but do not change allele frequencies
t
a population in which a trait is exposed to stabilizing selection over time (what happens to the average value of the trait and the variation)
the average value for the trait stays approx the same and the variation for the trait decreases
the upper forelimbs of bats and birds have fairly similar skeletal structures. but bat wings have a thin flap of skin stretched between the bones of the fingers and the arm, while bird wings consist of feathers extended all along the arm. how would you describe these relationships?
the forelimb skeletons of birds and bats are homologous, but the wings are due to convergent evolution