Evolution Exam 1 Flashcards
Biological evolution
changes in lineage of organisms over successive generations, descent with modification
Nonoverlapping magisteria
two worldviews that are not necessarily exclusive from one another
How do pathogens serve as evidence for evolution?
Antibiotic resistance occurs via a process of rapid evolution of pathogens. Some evidence that supports this is that the prevalence of resistant bacteria is correlated with the amount of antibiotic use
What are some reasons why resistant mutations for pathogens evolve quickly?
There is a rapid generation time since bacteria quickly reproduce, have a high mutation rate, and a large population size. Plasmid exchange can also occur between bacteria which further accelerates resistance
What are some incidences that serve as evidence of evolution in response to human activity?
In bighorn sheep human hunting is correlated with a smaller body size at sexual maturity
In an alpine plant commercial harvesting is correlated with increased incidence of camouflage
Elephants tracked over time were shown to lose their tusks with poaching pressure
Peppered moth developed camouflage (either as light grey or black) as urban areas developed. A single and recent mutational origin was identified and became prevalent due to gene flow
What are some examples of laboratory breeding experiments that serve as evidence for evolution? What about outside the lab?
Selection for change in morphology can show an upwardly selected line and downwardly selected line (more leg bristles in drosophila were downwardly selected)
Selection for change in behavior can be used to identify control lines and selected lines (female selection)
Domestication and crop domestication can be used to look at trends outside the lab
What are some examples of evidence showing a shared and common ancestry of present day species?
Fossil records can show transitional forms such as a tetrapod which was a transitional species between fish and limbed vertebrates. It had fish like characteristics (gills, scales, fins) and tetra pod like characteristics (shoulder, elbow, wrist, mobile neck).
Developmental genetics was also used to identify Hox genes which are expressed in both the paws of mice and fins of fish, and this points to a common ancestor
DNA sequencing can be used to look at the degree of shared genetic information between species and look at if that matches expected evolutionary relationships due to shared ancestry. Both the coding and noncoding regions of the genome can be used and the % of nucleotide divergence in any gene is proportional to how long ago the two lineages diverged
Homologous structures can also reflect a shared common ancestry
Biogeography can be used to find correlations between geographic distance and phenotypic similarities which reflect speciation from a shared ancestor from particular area
Essentialism
Also known as the platonic ideal. This is the Pre-Darwinian worldview that posits that everything in the universe has a single ideal form which is unchanging and “perfect” and that humans see the variable and “imperfect” earthly manifestations of that ideal. Under this notion variation = imperfection
How was the idea of essentialism applied to species?
Aristotle posited that each species has a single ideal form and that species can be arrayed along a single axis from the “lowest” or least complex to the “highest” or most complex on the “Great Chain of Being”
This was then incorporated into a biblical worldview known as “special creation” which posits that each species is created independently as part of a divine Creation and that species are unchanging
Thomas Malthus
Posited that resource limitation is an inevitable consequence of exponential growth and that all species, especially humans, produce more offspring than can survive
What was Darwin’s theory on evolution?
Darwin posited natural selection, where all species have the potential to exponentially reproduce but all species have limited resources. This means that there is always competition for resources within species and the best competitors differentially survive and reproduce. Credited Malthus for this
Darwin additionally posited that heritable traits that make some individuals better competitors will be disproportionately represented over successive generations causing gradual shifts
Worked with Alfred Russel Wallace to present to the Royal Society of London and Darwin published the Origin of Species a year later
What are five theories of evolution in the Origin of Species?
Species evolve over time, this idea was quickly accepted by Darwin’s contemporaries
Species have shared common ancestors, this was supported by paleontological, anatomical, and biogeographical data. In July 2016 more evidence was found supporting an origin of life in hydrothermal vents. Accepted by contemporaries
Gradualism where evolutionary change occurs through small, incremental steps. This was challenged by contemporaries including T. H. Huxley. Darwin believed sudden transformations of species were unscientific and gradual shifts did not invoke a supernatural element
Species diversification where divergence from common ancestors creates a multiplication of species. This means that speciation is a branching process and accounts for why there is a wide variety of species, explanation for biodiversity. Accepted by contemporaries
Natural selection which is the differential survival and reproduction of some individuals over others in a population due to phenotypic differences. This leads to favored traits being differentially represented in the next generation if they are heritable. Required integration with Mendelian genetics and population genetics before being accepted by contemporaries in 1940s
What are some misconceptions about natural selection?
Natural selection can lead to evolution but it refers to the differential survival and reproduction in one generation, does not look at successive generations
Natural selection does not create perfectly adapted organisms, it can create clumsy but workable solutions that reconcile trade offs (melanoma in fish results in increased sexual selection, long necks in giraffes means long nerves)
Evolution does not “progress” to any goal or purpose and there are no lower or higher species. No “missing links” since a great chain doesn’t exist. No species wild type since variation
Microevolution
Evolutionary change within a species, lots of focus on genetic changes over successive generations
Population genetics
Biological discipline that studies microevolutionary processes
Population
Group of individuals of the same species that live in geographical proximity and reproduce
Phenotypes
Measurable traits where variation may affect survival and reproductive success
Mc1r
Gene responsible for pigment variation in geese, jaguar, lizards, etc. Partially responsible for red hair phenotype in humans and other phenotypes such as anesthesia susceptibility
Discrete variation
Also known as Mendelian variation, refers to phenotypic variation that occurs in discrete classes. Qualitative traits such as a flower with 2 or 3 distinct colors are examples. Tends to be associated with simple inheritance and more uncommon in nature but is usually the focus of early genetic studies
Color of a clover plant corresponds to whether or not cyanide is produced from tissue damage (cyanogenesis). This is controlled by the Ac gene expression (substrate) and Li gene expression (hydrolyzing enzyme). If there is at least one dominant allele for both genes cyanogenesis results, it is an either/or scenario so falls under the discrete variation category
Continuous variation
Tends to fall along a normal distribution, quantitative traits such as human height and disease risk are examples. These are typically polygenic with complex genotype and environment interactions, tend to be more common in nature
What are some scenarios where phenotypic variation reflects the surrounding environment?
Ratio of red to far-red light wavelengths affects the height in plants where an ambient r:fr ratio results in elongated plants and a high r:fr ratio results in suppressed, shorter plants
In some turtle and alligator species, the temperature of egg incubation affects the sex determination and proportion of males in a clutch of eggs
What are some methods to determine whether a trait has a genetic basis?
Crosses can be constructed to segregate trait variation for discrete traits
Correlations between traits of parents and offspring can be observed, but there are often confounding variables in these traits since parents and offspring tend to be in similar environments. Additional data is often needed to make stronger conclusions such as carrying out observations in a controlled, standard environment
Common garden experiments in controlled, uniform environments, sometimes occurs in nature where samples are collected from similar environments
Genes
Previously defined as units of inheritance since genes and alleles were solely identified based on the phenotype they affect. Currently defined as units of transcription since some transcribed molecules are not translated such as ribosomal RNA
Haplotype
Allele at the DNA sequence level. For diploid organisms 2 alleles are present for gene and haplotypes may be identical (homozygous) or different (heterozygous)
What are common sources of variation between genes?
Single nucleotide polymorphisms (SNPs) result from point mutations
Insertions and/or deletions (Indel)
Within exons synonymous substitution can occur where a point mutation results in no amino acid change
Nonsynonymous substitutions can occur where a point mutation results in an amino acid change, this may not have a major effect on phenotype
Frameshift mutations result from insertions/deletions, often results from premature stop codons
Microsatellites are SSRs or simple sequence repeats. These are commonly used as genetic markers and determining biological diversity since there is a high mutation rate due to replication slippage and they result in high allelic variation in a population
Recombination due to meiosis
Linkage disequilibrium
Nonrandom associations in the inheritance of alleles at different loci, can be quantified with the term D, looks at patterns of genetic recombination in larger populations
What is the difference between linkage and linkage disequilibrium?
Linkage looks at the location of two genes on a chromosome in an individual, linkage disequilibrium looks at the degree of association between the inheritance of genes by measuring the level of recombination between two linked genes in a population
Pleiotropy
Single gene with multiple phenotypic effects
Epistasis
Interaction between different genes such that allelic variation at one gene affects the phenotypic expression of the other
Haplotype genealogy
Since mutations generate allelic variation, haplotypes can be sequenced to track mutations at a specific haplotype across generations
A rooted haplotype tree can be generated if we know which mutations arise first. But if haplotypes are sampled from a population and we don’t know the root of the tree, patterns of relationships can be inferred with an unrooted haplotype tree