Evolutionary Process and Phylogenics

Population level

Does evolution occur at the population level or individual level?

False

True or false: evolution is goal oriented.

False

True or false: evolution always leads to optimal traits.

Evolution

Change in the proportion of alleles within a population from generation to generation.

Population

Localized group of individuals that are capable of interbreeding and producing fertile offspring.

True

True or false: the hardy-weinberg equation assumes that the population is not evolving.

Hardy weinberg equation

Principle that uses allele proportions to calculate the expected proportions (in the population; sometimes incorrectly referred to as “frequencies”) of genotypes and phenotypes.

Natural selection

Organisms with traits suited to their environments are more likely to survive and reproduce.

Random mating

A mating system in which an individual is equally likely to mate with any other individual in the population, regardless of genotype.

Genetic drift

A random change in allele frequencies in a population.

Gene flow

Movement of alleles between populations.

Mutation

A change in the DNA sequence of a gene, resulting in new alleles.

Random mating, natural selection, genetic drift, gene flow, mutation.

The five conditions that must occur for the hardy-weinberg equation to be correct r______ m______, no n_____ s______, no g______ d______, no g_____ f_____, and no m_____.

Gene pool

The total set of alleles in a population at one time.

True

True or false: the gene pool takes the diploid genotypes of our individuals and breaks them down into the haploid genotype of their gametes.

P² +2pq+q²=1

What is the hardy weinberg equation?

The proportion of A1 alleles.

What is p?

The proportion of A2 alleles.

What is q?

False, it is a null model

True or false: the hardy-weinberg equation is used to predict what a population’s allele and genotype equilibrium proportions should be when it is evolving.

Positive assortative mating

Like mates with like, reduces proportion of heterozygotes for the trait that the basis of mate choice.

False

True or false: individuals produced by matings between related parents will have a higher fitness.

Mutation

Which of the following is typically the weakest evolutionary force?

Natural selection

Acts on the phenotype of the organism, alters the genetic composition of the population, and is the only evolutionary process that results in adaptations. Requirements: phenotypic variation in a trait, the trait is heritable, production of viable, fertile offspring is affected by the trait.

Fitness

The ability of an individual to produce offspring. If a very small and weak individual can produce more offspring than a large and strong individual, then the small individual is more fit.

Relative fitness

A comparison of the fitness typical of each phenotype. The proportion of alleles that are associated with phenotypes with high relative fitness will increase over time due to natural selection.

Adaptation

The evolutionary definition is a trait that increases the fitness of an individual in a particular environment (plays out over generations).

Acclimation

An adjustment in physiology or morphology that reduces the physiological stress of an individual (plays out within the lifetime of an individual).

No

Is acclimation a form of evolution?

Analogous traits or convergent traits

Similar traits that are not inherited from a common ancestor.

Vestigial traits

Structures that have no apparent function and appear to be residual parts from a past ancestor.

Directional selection

One extreme phenotypes is at an advantage, which increases the proportion of alleles causing that phenotype.

Stabilizing selection

Heterozygotes are at an advantage and become more common than their expected proportion. This selection maintains both alleles.

Disruptive selection

Heterozygotes are at a disadvantage and become less common, which can lead to the loss of one allele or the other.

Directional selection

Changes the average value of a trait.

Stabilizing selection

Reduces the amount of variation in a trait. Selects the intermediate values of the trait, which results in a narrower range of phenotypes.

Disruptive selection

Increases the amount of variation in a trait. Selects for two ends of a range, can result in balanced polymorphism or speciation in some circumstances.

Deleterious allele

When a gene is damaged.

Purifying selection hypothesis

If a gene is damaged (deleterious allele), the change will be inherited by all the offspring of an asexually reproducing individual. In contrast, only half (on average) of the offspring of a sexually reproducing individual will have the deleterious allele. Over time, this difference will steadily reduce the numerical advantage of asexual reproduction.

Paradox of sexual reproduction

Rapid evolution can enable a sexual population to eliminate a non-evolving competitor, even when that competitor has a reproductive advantage that substantially exceeds that arising from the two-fold cost of male production.

Changing environment hypothesis

If environmental conditions change, asexual reproduction is costly because it doesn’t generate enough genetic variation to respond to changes in temperature, moisture, predation/parasites, and competitors/food resources. On the other hand, sexual organisms can produce a variety of genetically different offspring, and some may have alleles in different combinations that give them an advantage in the new environment.

A

Which of the following statements about genetic drift is not true? A) Genetic drift can result in loss of alleles from a population. B) Genetic drift is random with respect to fitness (ability to pass genes on to the next generation). C) Genetic drift generally increases fitness in small populations. D) Genetic drift is an important evolutionary mechanism in small populations.

Genetic drift

Random combinations of gametes lead to genetic drift in finite populations, because some alleles are randomly represented more or less than would be expected from their proportions. Results in random changes in allele proportions. Does not result in adaptations.

Population size, time, and starting allele proportions.

The following affect the outcomes of genetic drift: p____ s______, t_____, and s_____ a_____ p_______.

True

True or false: the allele that is most likely to become fixed (proportion of 1.0) in a population is the most common allele at that time.

Population bottleneck and founder effect

The two general phenomena that reduce population size are p_____ b______ and f_____ e_____.

Population bottleneck

A relatively quick reduction in population size.

Founder effect

A small number of individuals that found a new population.

Founder effect

When a small group of individuals establishes a population in a new area. New population starts with a few individuals not genetically representative of a larger source population. The change

Gene flow

Occurs when individuals from a population breed with individuals from another population. Typically makes the populations more genetically similar. Can reduce local adaptation and can increase genetic variation and reduce inbreeding depression.

Mutation

Random changes in DNA. Results in new alleles, and these alleles can be deleterious, neutral, or advantageous. Rates of this are typically very small, and do not change allele proportions much.

Mutation

What is the most important for generating the genetic variation on which natural selection can act?

Geographic variation

Differences among populations in genetically based traits across the natural geographic range of a species. Reflects the cumulative balance of forces that cause divergence (e.g. selection, genetic drift) and forces that limit divergence (e.g. gene flow). Shows gradual spatial shift “cline”.

True

True or false: genetic drift causes divergence.

False

True or false: Selection limits divergence.

True

True or false: gene flow limits divergence.

Cline

A measurable gradient in a single characteristic (or biological trait) of a species across its geographical range.

Human races

Developed scheme of naming and grouping organisms that is still used today - played a major role in establishing scientific racism.

False

True or false: the categories of human races have biological basis.

True

True or false: nearly of all the genetic variation in humans can be found in Africa, meaning it contains the most genetic diveristy.

True

True or false: racial categorization has real biomedical consequences.

Tree of life

The theory that evolution by natural selection implies that all species come from preexisting species and that all species, past and present, trace their ancestry back to a single common ancestor.

Tree of life

A family tree of organisms that illustrates the hypothesized genealogical relationships among species, and has a single ancestral species at its base.

Node

Represents an ancestor that split into descendant groups.

Tip

Represents a group (taxon) that does not have descendants.

Sister taxa

Closest relatives on a tree; on adjacent branches arising from the same node.

Polytomy

More than two taxa arising from the same node; often used when relationships are not resolved.

Topology

The pattern of relationships a tree depicts.

False

True or false: rotating a phylogeny at a node changes its topology.

Cladogram

Branch length are arbitrary. Emphasis is on the branching pattern, which estimates evolutionary relationships among populations.

Phylogram

Branch length show the extent of genetic difference among populations. A scale bar is included.

Chronogram

Branch lengths show the extent of evolutionary time between nodes. A scale bar is included.

True

True or false: the different trees show estimated of the evolutionary relationships and have the same topology, but the phylogram and chronogram use branch lengths to provide additional information.

Homology

A shared character in two or more individuals or groups as the result of a single evolutionary event (e.g. bilateral symmetry).

Homoplasy (analogy)

A shared character in two or more individuals or groups as the result of more than one evolutionary event (e.g. segementation).

Phenetics

Based on the similarity of characters. Groups that are more similar are considered to be more closely related.

Cladistics

Species that have many shared, derived, characters are related.

Ancestral, derived

What are the two types of character sharing?

True

True or false: outgroups allow us to infer ancestral traits.

Outgroups

Part of the cladistics that give the relationship between the distantly related organisms and will act as the reference group for determining the evolutionary relationships between the other related groups that are called the ingroups.

Parsimony

The idea that the most likely explanation for a phenomenon is the simplest (or most economical).

Monophyletic group

An evolutionary group containing an ancestral population and all of its descendants.

Paraphyletic group

A group that includes an ancestral population and some of its descendants.

Polyphyletic group

A group whose members’ last common ancestor is not a member of the group.

Domain, kingdom, phylum, class, order, family, genus, species.

Do kindly place candy out for good spirits. (Least to most specific).

True

True or false: organisms are classified in a nested hierarchy of taxa.

Morphospecies concept

Species are assessed by comparing the traits of individuals. Similar individuals are considered to be the same species. Dissimilar individuals are considered to be different species. Advantages: easily applied to fossils, asexual organisms, and when tests of interbreeding are impractical. Disadvantages: very subjective - experts often disagree on how much difference is enough, and which differences matter.

Biological species concept

Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups. Advantages: based on functional differences, focuses studies of speciation on the origin of reproductive barriers. Limitations: often impractical or impossible to assess fossils, asexual species, and many living, sexual forms.

Prezygotic barriers

Impede mating and fertilization

Postzygotic barriers

Prevent offspring from successfully surviving and/or reproducing.

Speciation

Two things must happen for this to occur: individuals in a population must become genetically isolated from each other and form two populations, and the two populations must evolve differently from one another.

Allopatric

What type of speciation occurs when a population is geographically isolate from another (low gene flow)?

Vicariance

Allopatric speciation via _____ occurs when a previously connected population is divided geographically, stopping gene flow between the two new population. Both population sizes are typically relatively large. Driven by natural selection and weak genetic drift.

Dispersal

Allopatric variation via ______ occurs when a small number of individuals when a small number of individuals leave a population and establish a new population in a different location, and there is no gene flow between the two populations. Typically, one of the populations is large while the other is small. Driven by natural selection, genetic drift, and found effects.

Sympatric

What type of speciation occurs when a population is evolved into species while in the same geographic location, despite the potential for high gene flow?

Habitat preference

The type of sympatric speciation that occurs when individuals of species prefer different habitats within an area. Results in reduced gene flow as selection favors mating with individuals with a similar preference. Populations with different preferences diverge. Driven by natural selection and genetic drift.

Autopolyploidy

Type of sympatric speciation that occurs when there are multiple chromosome sets from the same species. An error in cell division that eventually results in diploid gametes, which can only produce viable and fertile offspring if they fuse with another diploid gamete. This results in immediate reproductive isolation from the rest of the population.

Allopolyploidy

Type of sympatric speciation that occurs when there are multiple chromosome sets from different species. Due to hybridization between species and doubling of chromosome number in F1 hybrids. “Homologous” chromosomes of two species might not synapse and separate correctly, resulting in nonfunctional gametes.

Fusion or extinction

What are the two possibilities if genetically divergent populations came back into contact with one another?

Reinforcement

The selection for mechanisms that prevent previously isolated population from interbreeding. If two populations have divereged extensively, the hybrid offspring may have a lower fitness than their parents.

Hybrid zones

Areas where persistent interbreeding between two species occurs, frequently resulting in hybrid offspring. Fitness of the hybrids and frequency of mating between species determines the spatial scale of the _______ and how long it exists.