Evolution, Speciation, and the History of Life

Comprehensive practice flashcards covering population evolution, Hardy-Weinberg equilibrium, natural selection modes, speciation mechanisms, early life origins, geological timelines, and phylogenetic classification.

How is evolution defined in the context of biological populations?

The gradual change in heritable traits, genes, or allele frequencies within a population of organisms over successive generations.

What are the three primary sources of genetic variation within a population?

1. Formation of new alleles (mutation)
2. Altering gene number or position (chromosomal changes)
3. Sexual reproduction (crossing over, independent assortment, and fertilization)

What are the five conditions required for a population to remain in Hardy-Weinberg equilibrium?

1. No mutations
2. Random mating
3. No natural selection
4. Extremely large population size
5. No gene flow

Under Hardy-Weinberg conditions, what is the consequence if the condition of random mating does not hold?

If individuals mate within a subset of the population (such as near neighbors or inbreeding), random mixing of gametes does not occur and genotype frequencies change.

What is the consequence if a population size is small rather than extremely large under Hardy-Weinberg conditions?

Allele frequencies fluctuate by chance over time in a process called genetic drift.

In the Hardy-Weinberg equation $p + q = 1$, what do $p$ and $q$ represent?

$p$ represents the frequency of the dominant allele ($A$), and $q$ represents the frequency of the recessive allele ($a$).

In the Hardy-Weinberg equation $p^2 + 2pq + q^2 = 1$, what do the terms $p^2$, $2pq$, and $q^2$ represent?

$p^2$ represents the frequency of the homozygous dominant genotype ($AA$), $2pq$ represents the frequency of the heterozygous genotype ($Aa$), and $q^2$ represents the frequency of the homozygous recessive genotype ($aa$).

What are the three main mechanisms that cause evolution in populations?

Natural selection (adaptive evolution), genetic drift, and gene flow.

What is genetic drift, and how does it impact small populations?

A process in which chance events cause allele frequencies to fluctuate unpredictably from one generation to the next, reducing genetic variation due to random loss.

How is gene flow defined?

The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.

Which three modes of natural selection on a phenotypic distribution are shown in diagrams (a), (b), and (c)?

(a) Directional selection (favors one extreme) (b) Disruptive selection (favors both extremes) (c) Stabilizing selection (favors intermediate variants)

What is sexual dimorphism?

A difference in secondary sexual characteristics between the sexes, such as differences in size, color, ornamentation, and behavior.

What is the difference between intrasexual selection and intersexual selection?

Intrasexual selection is direct competition among individuals of one sex (often males) for mates of the opposite sex, whereas intersexual selection (mate choice) occurs when individuals of one sex (usually females) are choosy in selecting their mates.

Which evolutionary phenomenon is depicted in this diagram?

The Founder Effect, which occurs when a few individuals become isolated from a larger parent population, establishing a colony with different allele frequencies.

What specific form of genetic drift is illustrated in this diagram?

The Bottleneck Effect, which occurs when a drastic reduction in population size results from a sudden environmental change, leaving a surviving gene pool that may no longer reflect the original population.

What are the four major species concepts?

1. Biological Species Concept
2. Morphological Species Concept
3. Phylogenetic Species Concept
4. Ecological Species Concept

How does the Biological Species Concept define a species?

A group of populations whose members have the potential to interbreed and produce viable, fertile offspring with members of other such groups, and who are reproductively isolated from other species.

What is the distinction between pre-zygotic and post-zygotic reproductive barriers?

Pre-zygotic barriers prevent fertilization from happening, whereas post-zygotic barriers impact the survival or reproductive capability of offspring after fertilization.

What are the three steps in the origin of new species from existing populations?

Step 1: Reproductive Isolation (a barrier to gene flow is established) Step 2: Natural selection and evolution (populations diverge genetically) Step 3: Complete divergence (reproductively isolated new species with no interbreeding)

What is the difference between allopatric speciation and sympatric speciation?

Allopatric speciation involves geographic isolation of populations that interrupts gene flow and leads to independent evolution. Sympatric speciation involves new species evolving from a single ancestral species while living in the same geographic region (gene flow reduced without geographic separation).

What is adaptive radiation?

The adaptation (via genetic mutation) of an organism that enables it to successfully spread, or radiate, into other environments, leading to speciation.

Which models of speciation rates are illustrated in diagrams (a) and (b)?

(a) Punctuated Equilibrium (new species diverge quickly and then change very little) (b) Gradual model (new species diverge slowly and steadily over long periods of time)

What four sequential chemical and physical processes led to the origin of early life?

1. Abiotic synthesis of small organic molecules (e.g., amino acids, nitrogenous bases)
2. Small molecules forming macromolecules (e.g., nucleic acids and proteins)
3. Macromolecules packaged into membrane-bound protocells
4. Origin of self-replicating molecules

Why was DNA favored over RNA as the primary genetic material after life originated?

DNA is more chemically stable than RNA and can be replicated more accurately.

What is meant by the half-life of a radioactive isotope?

The time required for $50\%$ of the "parent" isotope to decay into a "daughter" isotope at a known rate.

What are the half-lives of Carbon-14 and Uranium-238 specified in the notes?

Carbon-14 has a half-life of $5{,}730\text{ years}$, and Uranium-238 has a half-life listed as $238\text{ billion years}$.

What concept does this decay graph demonstrate across successive time intervals?

Radiometric decay showing the fraction of parent isotope remaining halving each period ($\frac{1}{2}$, $\frac{1}{4}$, $\frac{1}{8}$, $\frac{1}{16}$) while daughter isotopes accumulate.

Approximately when did Earth originate, and during which geologic eon?

Approximately $4.6\text{ billion years ago}$ during the Hadean eon.

When did the Cambrian Explosion take place, and why is it significant?

It occurred roughly $535\text{--}525\text{ mya}$ and marked the rapid diversification and appearance of major animal phyla.

What geological feature is shown in this rendering off the coast of Mexico, and what event formed it?

The Chicxulub Crater (~$110\text{ mi}$ wide, ~$12\text{ mi}$ deep), formed $66\text{ mya}$ by an asteroid impact (~$10\text{--}15\text{ mi}$ wide) that triggered the Cretaceous mass extinction.

What supercontinent formed about $250\text{ million years ago}$ through plate tectonic movement?

Pangaea.

Who is known as the "Father of Taxonomy," and what were his main contributions?

Carolus Linnaeus (1707–1778), a Swedish naturalist who published Systema naturae (1748), created hierarchical classification, introduced binomial nomenclature, and described over $13{,}000$ species into two kingdoms (Plants and Animals).

What is the complete sequence of taxonomic classification from broadest to most specific?

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

In a phylogenetic tree, what do the root and a node represent?

The root represents the most recent common ancestor of all taxa in the tree; a node represents the common ancestor of two diverging lineages.

In phylogenetics, what defines a basal taxon and sister taxa?

A basal taxon is a lineage that diverges early in the history of a group from all other members (e.g., fishes relative to tetrapods); sister taxa share an immediate common ancestor not shared by any other group.

What is the difference between a derived trait (synapomorphy) and an ancestral trait (plesiomorphy)?

A derived trait (synapomorphy) is a trait that developed within a specific lineage, whereas an ancestral trait (plesiomorphy) is a trait that was already present in the common ancestor.

In cladistics, what is the distinction between monophyletic, paraphyletic, and polyphyletic groups?

Monophyletic: includes an ancestor and ALL of its descendants. Paraphyletic: includes an ancestor and SOME of its descendants. Polyphyletic: includes descendants of multiple ancestors.

What is an outgroup in phylogenetic tree construction?

A species or group of species from an evolutionary lineage that is closely related to, but not a part of, the group of species being studied (the ingroup).