Chapter 15 Micro/Macro Evolution Flashcards
Define the gene pool, a population, and microevolution.
population-group of individuals of the same species likely to mate with each other
microevolution-change in allele frequency over time
gene pool-genes available in a population
Explain how mutation and sexual recombination produce genetic variation.
The genetic variation on which evolution depends originates when mutation, gene duplication, or other processes produce new alleles and new genes. Many new genetic variants can be produced in short periods of time in organisms that reproduce rapidly. Sexual reproduction can also result in genetic variation as existing genes are arranged in new ways.
new alleles can arise by mutation, a change in the nucleotide sequence of an organism’s DNA. a mutation is like a shot in the dark—we cannot predict accurately which segments of DNA will be altered or in what way. In multicellular organisms, only mutations in cell lines that produce gametes can be passed to offspring.
In organisms that reproduce sexually, most of the genetic variation in a population results from the unique combination of alleles that each individual receives from its parents. Of course, at the nucleotide level, all the differences among these alleles have originated from past mutations and other processes that can produce new alleles. But it is the mechanism of sexual recombination that shuffles existing alleles and deals them at random to produce individual genotypes.
Describe the five conditions required for the Hardy-Weinberg equilibrium. Explain the significance of the Hardy-Weinberg equilibrium to natural populations.
No mutations- The gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated
random mating-if individuals mate preferentially within a subset of the population, such as their close relatives (inbreeding) random mixing of gametes does not occur and genotypic frequencies change
no natural selection-Differences in the survival and reproductive success of individuals carrying different genotypes can alter allele frequencies
extremely large population size-The smaller the population, the more likely it is that allele frequencies will fluctuate by chance from one generation to the next (genetic drift)
no gene flow-By moving alleles into or out of populations, gene flow can alter allele frequencies
*significance=it can’t occur in real life
Define genetic drift and gene flow. Explain how the bottleneck effect and the founder effect influence microevolution.
Genetic Drift: change in the gene pool of a population due to chance (nothing to do with adaptation, i.e. who is the fittest)
Gene Flow: the movement of individuals or gametes between populations
The bottleneck effect is an event, like a random natural disaster, that drastically reduces population size. When the population is drastically reduced, the allele frequencies are drastically altered as well.
the founder effect is the colonization of a new location by a small number of individuals. Because there are a small number of individuals, there is a smaller gene pool and therefore there is more likely to be a higher allele frequency of some sort within that population. (((For example: the 6 finger gene that Amish people have - someone within the original Amish group carried the 6 finger allele and now it is prevalent in Amish people because they don’t often intermarry with people outside of their population.)))
Explain why natural selection is the only mechanism that leads to adaptive evolution.
Natural selection happens based upon the notion that the “best adapted individuals have the most reproductive success.” Individuals with traits best adapted to their environments combine to let him/her have a stronger fitness level, aka stronger reproductive success, and therefore able to pass on their genes to the next generation. These genes are then passed on to the next generations as adaptations, aka inherited traits that enhance fitness in environment.
Distinguish between stabilizing selection, directional selection, and disruptive selection. Describe an example of each.
Stabilizing selection: occurs when phenotypes at both extremes of the phenotypic distribution are selected against. This narrows the range of variation. An example is human birth weight. Babies that are very large or very small at birth are less likely to survive. This keeps birth weight within a relatively narrow range.
Directional selection occurs when one of two extreme phenotypes is selected for. This shifts the distribution toward that extreme. This is the type of natural selection that the Grants observed in the beak size of Galápagos finches.
Disruptive selection occurs when phenotypes in the middle of the range are selected against. This results in two overlapping phenotypes, one at each end of the distribution. An example is sexual dimorphism . This refers to differences between the phenotypes of males and females of the same species. In humans, for example, males and females have different heights and body shapes. Or rock pocket mice, where medium colored mice don’t survive anywhere.
Explain how sexual selection may lead to phenotypic differences between males and females.
sexual selection is a specific type of natural selection that selects for creatures that are best suited to attract the opposite sex mate. For example, male peacocks adapted to have long feathers that attract females. The males with the feathers were selected for, thus creating a phenotypic difference between males and females.
Explain how genetic variation is maintained in populations.
Heterozygote advantage. Example: sickle cells help fight malaria. So, if this weren’t the case, people with sickle cell anemia would possibly have died out because there would be no advantage to having sickle cell. But because there is an advantage, variation remains. In heterozygote advantage, the heterozygotes have an advantage over homozygous recessive and dominant individuals.
Frequency-dependent selection: the term given to an evolutionary process where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population. Predators can catch on! An example of this: Harmless scarlet kingsnake mimics the coral snake, but its pattern varies less where the coral snake is rare.
Neutral variation: neither harmful nor advantageous. Therefore, variation remains. Example: widows peak
diploidy-in diploid eukaryotes, a considerable amount of genetic variation is hidden from selection in the form of recessive alleles. Recessive alleles that are less favorable than their dominant counterparts, or even harmful in the current environment, can persist by propagation in heterozygous individuals. This latent variation is exposed to natural selection only when both parents carry the same recessive allele and two copies end up in the same zygote. This happens only rarely if the frequency of the recessive allele is very low. Heterozygote protection maintains a huge pool of alleles that might not be favored under present conditions, but which could bring new benefits if the environment changes
balancing selection-selection itself may preserve variation. Balancing selection occurs when natural selection maintains two or more formed in a population. This type of selection includes heterozygote advantage and frequency dependent selection
Give four reasons why natural selection cannot produce perfection.
Selection can act only on existing variation-Natural selection favors only the fittest phenotype among those currently in the population, which may not be the ideal traits. New advantageous alleles do not arise on demand
evolution is limited by historical constraints-each species has a legacy of descent with modification from ancestral forms. Evolution does not scrap the ancestral anatomy and build each new complex structure from scratch; rather, evolution co-opts existing structures and adapts them to new situations. We could imagine that if a terrestrial animal were to adapt to an environment in which flight would be advantageous, it might be best just to grow an extra pair of limbs that would serve as wings. However, evolution does not work this way; instead, it operates on the traits an organism already has. Thus, in birds and bats, an existing pair of limbs took on new functions for flight as these organisms evolved from non flying ancestors.
adaptations are often compromises-Each organism must do many different things. A seal spends part of its time on rocks; it could probably walk better if it had legs instead of flippers, but then it would not swim nearly as well. We humans owe much of our versatility and athleticism to our prehensile hands and flexible limbs, but these also make us prone to sprains, torn ligaments, and dislocations: Structural reinforcement has been compromised for agility
chance, natural selection, and the environment interact-
Chance events can affect the subsequent evolutionary history of populations. For instance, when a storm blows insects or birds hundreds of kilometers over an ocean to an island, the wind does not necessarily transport those individuals that are best suited to the new environment. Thus, not all alleles present in the founding population’s gene pool are better suited to the new environment than the alleles that are “left behind.” In addition, the environment at a particular location may change unpredictably from year to year, again limiting the extent to which adaptive evolution results in a close match between the organism and current environmental conditions.
Define and distinguish between microevolution and macroevolution.
Microevolution: the change in allele frequency over time.
Macroevolution: speciation - the formation of new species. Microevolution leads to macroevolution.
Compare the definitions, advantages, and disadvantages of the different species concepts.
While the biological species concept emphasizes the separateness of species from one another due to reproductive barriers, several other definitions emphasize the unity within a species. For example, the morphological species concept characterizes a species by body shape and other structural features. The morphological species concept can be applied to asexual and sexual organisms, and it can be useful even without information on the extent of gene flow. In practice, this is how scientists distinguish most species. One disadvantage, however is that this definition relies on subjective criteria; researchers may disagree on which structural feature distinguishes a species.
The ecological species concept views a species in terms of its ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment. For example, two species of salamanders might be similar in appearance but differ in the foods they eat or in their ability to tolerate dry conditions. Unlike the biological species concept, the ecological species concept can accommodate asexual as well as sexual species. It also emphasizes the role of disruptive natural selection as organisms adapt to different environmental conditions.
The phylogenetic species concept defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life. Biologists trace the phylogenetic history of a species by comparing its characteristics, such as morphology or molecular sequences, with those of other organisms . Such analyses can distinguish groups of individuals that are succiciently different to be considered separate species. Of course, the difficulty with this species concept is determining the degree of difference required to indicate separate species.
Describe five types of prezygotic barriers and three types of postzygotic barriers that prevent populations belonging to closely related species from interbreeding
Prezygotic
Temporal Isolation: mating or flowering occurs at different seasons or time of day
Habitat Isolation: populations live in different habitats and do not meet
Behavioral Isolation: There is little or no sexual attraction between different species
Mechanical Isolation: Structural differences in genitalia or flowers prevent copulation or pollen transfer
Gametic Isolation: Male and/or female gametes die before uniting or fail to unite
Postzygotic
Reduced hybrid viability: hybrids fail to develop or to reach sexual maturity
Reduced hybrid fertility: hybrids fail to produce functional gametes
Hybrid breakdown: offspring of the hybrids are weak or infertile
Explain how geologic processes can fragment populations and lead to speciation.
A species is a group of organisms that can breed and produce fertile offspring together in nature. For a new species to arise, some members of a species must become reproductively isolated from the rest of the species. This means they can no longer interbreed with other members of the species. How does this happen? Usually they become geographically isolated first.
Assume that some members of a species become geographically separated from the rest of the species. If they remain separated long enough, they may evolve genetic differences. If the differences prevent them from interbreeding with members of the original species, they have evolved into a new species. Speciation that occurs in this way is called allopatric speciation
lack of gene flow - more differences between population.
Explain how reproductive barriers might evolve in isolated populations of animals.
Reproductive barriers may evolve as populations diverge, and then reproductive barriers keep species separate.
Explain how sympatric speciation can occur and how it typically happens in plants.
Sympatric Speciation: a new species arises within the same geographic area as a parent species.
New species are polyploid - meaning that their cells have more than two complete sets of chromosomes. This occurs most commonly in plants due to self-fertilization.
Habitat differentiation - occurs most commonly in animals. (fruit flies and apple orchard example)
Sexual selection - occurs in animals, in which females choose mates based on coloration - isolating populations and keeping gene pools of newly forming species separate.
