BIOL 0480 - Exam 1

4 Conditions for Evolution by Natural Selection

1. Variation in the population 2. Variation has a genetic basis (trait is heritable) 3. differential survival or reproduction (not everyone can survive) 4. differential survival is associated with genetic variation (not everyone surviving has genetic basis)

Define Mutation Selection Balance

A balance of evolutionary forces (mutation and selection) that can maintain variation in a population. If a deleterious allele is introduced by mutation, but removed by selection it can be maintained by this balance. Evidence for the interaction of evolutionary forces

Define Local Fitness Peak

A condition of intermediate average fitness for a local population with a particular genetic composition in Wright's Adaptive Landscape model. The local peak is lower than the 'global fitness peak' that has the combination of alleles that result in the highest fitness. It is important in illustrating that selection may not be able to reach optimal fitness when acting as the sole evolutionary force

Define Multiple Niche Polymorphism

A polymorphism that is maintained by differential selection in multiple niches. If alternative genotypes have higher fitness in alternative environments (niches), the average effect can result in heterozygotes having the highest fitness, resulting in balancing selection. Demonstrates the importance of different fitness values in different environments

Define Vestigial Structure

A structure that is more pronounced or evident in an ancestor than in a descendant indicating a loss of function in the descendant. Provides evidence for the costly nature of maintaining structures, and for descent with modification, a general definition of evolution

Define Vestigial Character

A trait that has been reduced in size or structure from lack of use, relative to a homologous trait in related organisms. Demonstrated that traits can be costly and natural selection will lead to their loss without the ongoing fitness benefits of needing to use such traits

Define and state distinction between Absolute fitness and Relative fitness

Absolute fitness - quantifies some measurement of fitness for a particular genotype without reference to other genotypes, such as total offspring produced or growth rate Relative fitness - a comparative measure of fitness, with reference to the most-fit genotype or individual. Relative fitness is determined by dividing the given genotype's absolute fitness but the highest absolute fitness in the population

Define and state distinction between Candidate Gene and Neutral Marker

Candidate Gene - a gene whose function is known and is a likely genetic factor in explaining variation in a particular phenotype. Neutral Marker - a SNP or other genetic marker that has no known function or is believed not to be related to the trait being studied Inference of genotype-phenotype association from a candidate gene is made more reliable when a neutral marker shows no association

Define ∆p

Change in allele frequency over some interval of generations. ∆p = pt+1 - pt. An incremental measurement of microevolution, and can be driven by any evolutionary force

Define Isolation by Distance

Decreased genetic similarity of populations with increasing distance of geographic separation. Provides evidence for reduced gene flow or migration, either by geographic barriers or simple migration distances. Important in describing differentiation between populations

Define and state distinction between Directional Selection and Stabilizing Selection

Directional Selection - selection towards one phenotype or a specific genotype, such as when AA is favored over Aa or aa. Stabilizing Selection - selection towards the 'middle' of the phenotype distribution, or higher fitness for heterozygotes. Balancing selection is one form of stabilizing selection the distinction is that directional selection leads to a shift in the mean phenotype, while stabilizing selection preserves the mean phenotype

Define and state distinction between Monophyly and Polyphyly

Monophyly - a group of organisms descended from a single common ancestor. Important in determining true ancestor-descendant relationships in phylogenetics Polyphyly - a group descended from more than one common ancestor. Commonly results from using analogous characters that are similar in form, but not due to descent. Homology and analogy are distinguishing features

Define Frequency Dependent Selection

Selection on an allele that varies with the frequency of that allele. Typically this involves rare-allele advantage, so the alleles cycle, such that it increases when rare but decreases when common. A process that can maintain genetic variation in populations

Define Purifying Selection

Selection that eliminates deleterious traits, mutations, or alleles, from populations. Acts to reduce variation in populations and maintains "wild type"

Define and state distinction between Selective Sweep and Hitchhiking

Selective Sweep- the increase in frequency of a beneficial allele due to directional selection, and the 'sweeping; of variation in the chromosomal region of the beneficial allele Hitchhiking - the effect that the selective sweep has on linked variants adjacent to the beneficial mutation. By being linked on the chromosome, the sites hitchhike up to high frequency, resulting in the loss of variation. the distinction is the focus on the beneficial allele (driver of the sweep) and the possibly neutral linked sites that come along for the ride.

Define Homology

Similarity of form due to descent from a common ancestor. Reflects the true ancestry of a character or trait and is an essential component of phylogenetic analysis

Define Effective Population Size

The effective number of breeding individuals in a population. Contrasts with the census size or total number of individuals. This reflects the genetically relevant population size and determines the strength of genetic drift

Define Founder Effect

The establishment of a population by a small number of founders, leading to the loss of genetic variation and imposing genetic drift on the population. A process where evolution can occur by non-selective forces, and can be important in generating population structure or variation between populations