Biology Flashcards 19-24

Flashcards on Early Life, Diversification of Prokaryotes, Origin of Species, Genetic Variation, Phylogeny, and Evidence of Evolution

Prokaryotes

The oldest fossil organisms, dating back to 3.5 billion years ago.

Protocells

Membrane-bound droplets that maintain consistent internal chemistry.

Ribozymes

Single-stranded RNA molecules that have 3D shapes, making catalytic function possible; some are also self-replicating.

Plasmids

Smaller DNA rings found in some prokaryotic species.

Obligate aerobes

Prokaryotes that require O2 for cellular respiration.

Obligate anaerobes

Prokaryotes that are poisoned by O2; either use fermentation or anaerobic respiration with substances other than O2 as final electron acceptors.

Facultative anaerobes

Prokaryotes that can use O2 when present or carry out fermentation or anaerobic respiration.

Species

A group of populations whose members can interbreed and produce viable, fertile offspring.

Speciation

The process of one species splitting into two or more species.

Reproductive isolation

Barriers preventing two species from successfully reproducing.

Prezygotic barriers

Barriers that block mating and/or fertilization.

Habitat isolation

Species occupy different habitats.

Temporal isolation

Species breed at different times of the day/seasons/years.

Behavioral isolation

Courtship rituals differ between species.

Mechanical isolation

Morphological differences prevent successful mating.

Gametic isolation

Sperm cannot fertilize eggs.

Postzygotic barriers

Barriers that prevent the hybrid zygote from developing into a viable, fertile adult.

Reduced hybrid viability

Hybrids die early.

Reduced hybrid fertility

Hybrids are sterile (no gametes).

Hybrid breakdown

First or second-generation hybrids are fertile, but subsequent generations lose fertility.

Allopatric speciation

Speciation that occurs with geographic isolation.

Sympatric speciation

Speciation that occurs without geographic isolation.

Polyploidy

The presence of extra sets of chromosomes due to accidents during cell division.

Punctuated equilibria

Drastic change followed by long periods of no change, resulting in a fast rate of speciation.

Gradualism

Small changes throughout time, resulting in a slow rate of speciation.

Genetic variation

Differences among individuals in the composition of their genes or other DNA segments.

Neutral variation

Genetic variation that does not confer a selective advantage or disadvantage.

Population

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

Gene pool

The aggregate of all copies of every type of allele at all loci in every individual in a population.

Hardy-Weinberg equilibrium

A population in which allele and genotype frequencies remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work.

Genetic drift

A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next.

Founder effect

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.

Bottleneck effect

Genetic drift that occurs when the size of a population is reduced, by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.

Gene flow

The transfer of alleles from one population to another.

Relative fitness

The contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.

Phylogenetic tree

A branching diagram that represents a hypothesis about the evolutionary history of a group of organisms.

Branch point

Represents the common ancestor of two evolutionary lineages diverging from it.

Basal taxon

In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group.

Clades

A group of species that includes an ancestral species and all its descendants.

Shared ancestral character

A character, shared by members of a particular clade, that originated in an ancestor that is not a member of that clade.

Shared derived character

An evolutionary novelty that is unique to a particular clade.

Molecular clock

A method for estimating the time required for a given amount of evolutionary change, based on the observation that some genes and other regions of genomes evolve at constant rates.

Homologous Structures

Structures in different species that are similar because of common ancestry.

Vestigial Structures

A feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors.

Convergent Evolution

The evolution of similar features in independent evolutionary lineages.

Biogeography

The study of the past and present geographic distribution of species.

Evolution

Descent with modification; the idea that living species are descendants of ancestral species that were different from the present-day ones; also defined more narrowly as the change in the genetic composition of a population from generation to generation.

Adaptations

inherited characteristic of an organism that enhances its survival and reproduction in a specific environment.

Natural Selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Artificial Selection

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.

Evolutionary Fitness

The proportional contribution an individual makes to the gene pool of the next generation.

Population

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