23 Flashcards
microevolution
a change in allele frequencies in a population over generations
macroevolution
results in the formation of new species or large groups of living things
genotype
genetic makeup of any organism
phenotype
observable traits that an organism has (including physical characteristics and behavior)
genes come in varying forms called _____
alleles
the basis of evolution is ____
a change in the frequency of alleles in
a population
natural selection
The effects of the mutations on the survival and reproduction of organisms
population
a localized group of interbreeding individuals
gene pool
collection of alleles in the population
allele frequency
how common is that allele in the population
what are the conditions for the Hardy Weinberg equation?
- No mutations
- Random mating
- No Natural Selection
- Very large population size
- No gene flow
Mechanisms that cause evolution are
- mutation
- genetic drift
- gene flow
- natural selection
mutation
modifies allele frequencies by continually introducing new alleles. The alleles may be beneficial or detrimental or have no effects on fitness
genetic drift
causes allele frequencies to change randomly. In some cases, drift can cause alleles that decrease fitness to increase in frequency
gene flow
occurs when individuals leave one population, join another, and breed. Arriving individuals introduce new alleles and departing individuals remove alleles; resulting in change in allele frequencies
natural selection
increases the frequency of certain alleles—the ones that contribute to success in survival and reproduction
Genetic drift can have large effects on small populations through two common scenarios which are
– Founder effects
– Population bottlenecks
founder effect
a change in allele frequencies that occurs when a new population is established (i.e. a subpopulation migrates)
bottleneck effect
a sudden reduction in the number of alleles present in a population. By chance alone, certain alleles may be overrepresented among survivors, while others are underrepresented or absent.
genetic drift can
- …is significant in small populations
- …can cause allele frequencies to “drift”
randomly - …can lead to a loss of genetic variation within populations
- …can lead to the fixation of deleterious alleles
Gene flow can _____ the fitness of a population
increase
types of natural selection
directional, disruptive, stabilizing
directional
average phenotype of the population is changed in one direction. (favors one extreme)
disruptive
eliminates phenotypes near the average value. (favors extremes)
stabilizing
selection reduces both extremes in a population, so that there is no change in the average value of a trait over time and genetic variation is reduced. (favors average)
sexual selection
is a form of natural selection that can affect the frequency of alleles in a gene pool.
– It occurs when differences in reproductive success arise because of differential success in mating.
sexual dimorphism
a difference in secondary sexual characteristics between males and females
intrasexual selection
is direct competition among individuals of one sex (often males) for mates of the opposite sex
Intersexual selection
often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates
• Showiness of male appearance can increase a male’s chances of attracting a female while decreasing his chances of survival
neutral variation
is genetic variation that does not confer a selective advantage or disadvantage
preservation of genetic variation comes from
neutral variation, diploidy, balancing selection
diploidy
in diploid eukaryotes,a considerable amount of genetic variation is
hidden from selection in the form of recessive alleles
What is the smallest unit that can evolve?
populations
natural selection acts on ____
individuals (inheritable traits)
Describe the role of mutation in evolution.
New alleles can arise by mutation: a change in the nucleotide sequence of an organisms DNA
Some mutations can be harmful, others are not. Neutral variation- differences in DNA sequences that do not confer a selective advantage or disadvantage
List 5 agents of change that can bring about evolution. What is it about natural selection that is unique compared to the other agents of change?
- Mutation
- gene flow
- nonrandom mating
- genetic drift
- natural selection
Natural Selection is the only mechanism acting alone can result in ADAPTATION.
Most of the mechanisms lead to ____ of genetic diversity except for mutation
LOSS
natural selection
identify whether they increase, decrease or have no effect on average fitness and genetic variation.
Natural selection: It favors certain beneficial alleles.
It can lead to maintenance, increase, or reduction of genetic variation.
Its effect on average fitness is that it can produce adaptation
genetic drift
identify whether they increase, decrease or have no effect on average fitness and genetic variation.
It tends to reduce genetic variation, via loss or fixation of alleles.
Its effects on average fitness is that it reduces average fitness by the fixation of alleles or loss of alleles
mutation
identify whether they increase, decrease or have no effect on average fitness and genetic variation.
It produces new alleles.
It increases genetic variation by introducing new alleles
It is random with respect to fitness. Mutations may be beneficial, detrimental, or may have no effect on fitness
Gene flow
identify whether they increase, decrease or have no effect on average fitness and genetic variation.
Gene Flow may increase genetic variation by introducing new alleles or it may decrease variation by removing alleles.
Gene Flow may increase average fitness by introducing high-fitness alleles or decrease it by introducing low-fitness alleles
biological fitness
the ability to survive to reproductive age, find a mate, and produce offspring.
True or False—“Survival of the Fittest” is an accurate description of evolution by natural selection. Why or why not?
False.
Natural selection is not so much about which traits are beneficial and which traits are not as useful for a specific species. Rather, natural selection is much more about the number of offspring an organism leaves behind that reach a reproductive age or fitness. Natural selection is more about reproductive success than ruling out certain traits of certain species.
Describe the general model for the evolution of resistance (among bacteria, or insects, or fungi etc)
Once the antibiotic is introduced before selection, all non-resistant organisms die off, than after selection the population consists of organisms that are able to resist the antibiotic, therefore the final population will consist of all resistant organisms
Define gene flow, give an example.
the transfer of alleles into or out of a population due to movement of fertile individuals or their gametes
Human migration is transferring alleles between populations that were once isolated
Is genetic drift more likely to happen in small or large populations?
Small populations
Since the population is small it has a more of possibility of losing alleles entirely. When this happens, the remaining alleles eventually become fixed.
“The common phenotype is not necessarily the most adaptive”. Explain this statement.
Whether or not a trait is common has to do with how many copies of that gene version (or allele) are in the population. It has little or nothing to do with whether the trait is dominant or recessive
what mechanism preserve genetic variation?
- Diploidy
- Heterozygote advantage
- Frequency-dependent selection
diploidy
in diploid eukaryotes, a considerable amount of genetic variation is hidden from selection in the form of recessive alleles; heterozygotes can carry recessive alleles that are hidden from the effects of selection
Heterozygote advantage
natural selection tends to maintain two or more alleles at that locus
Frequency-dependent selection
fitness of a phenotype depends on how common it is in the population
Natural selection changes allele frequencies because some _______ survive and reproduce more successfully than others.
individuals
No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is
the reshuffling of alleles in sexual reproduction.
If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?
gene variability = 0%; number of alleles = 1
There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is most likely an example of
genetic drift
A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?
0.42
p = 0.7 q = 0.3
2 (0.7 x 0.3) = 0.42
Hardy Weinberg describes the gene pool of a population that is _____
NOT evolving
Is the soapberry bug/golden rain tree example an illustration of microevolution or macroevolution?
Microevolution – population
allele
Genes come in varying forms which are called alleles
genetic variation
phenotypic variations are differences among individuals in the composition of their genes
what are sources of genetic variation?
- mutation - formation of new alleles
- sexual reproduction
- altering gene number or position
genetic variants can be produced rapidly in organisms with a _____
short generation time
natural selection is the only mechanism that causes ____
adaptive evolution
what are effects of genetic drift?
- significant in small populations
- causes allele frequencies to change randomly
- can lead to a loss of genetic variations
- can cause harmful alleles to become fixed
what is biological fitness and how is it measured?
Ability of an individual to produce surviving, fertile offspring relative to that ability in other individuals in the population, measurable quantity
Count the number of healthy fertile offspring produced by different individuals in a population
Measures the reproductive success of an organism relative to others in a population
relative fitness
the contribution an individual makes on the gene pool of the next generation relative to the contributions of other individuals.
selection acts more directly on the phenotype, than the genotype
Most reproductive output =
highest fitness
sexual selection
a process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates
reasons why natural selection can’t fashion perfect organism
- selection can act only on existing variations
- evolution is limited by historical constraints
- adaptations are often compromises
