Biology 1B - Key Terms, Units 1-3

Adaptation

A trait gained by natural selection that enhances the ability of an organism to survive or reproduce in a particular environment.

Alleles

Alternative versions of genes that differ in nucleotide sequence. Different alleles may produce differences in character expression (i.e., phenotypic differences).

Deoxyribonucleic Acid (DNA)

The molecule of inheritance in most organisms; a double-stranded helical molecule consisting of long sequences of four nucleotides.

Nucleotides

Adenine (A), thymine (T), cytosine (C), and guanine (G).

Differential Success

The greater survival and reproduction of organisms with some traits compared with organisms that do not have those traits.

Evolution

Change over time in the genetic composition of species; allele frequencies may change as a result of mutation, natural selection, genetic drift, or gene flow.

Fixation

The change in a gene pool from a situation where there are at least two variants of a particular gene (allele) to a situation where all individuals possess only one of the alleles.

Gene

A section of a DNA strand (i.e., a sequence of nucleotides) that determines the sequence of amino acids in the protein for which it codes.

Gene flow

The movement of genes among populations due to migration and interbreeding.

Genetic Drift

Random changes in allele or genotype frequencies within a population.

Genotype

The set of genes that an organism carries. Genotype can also refer to the set of alleles for a particular gene.

Heritability

The genetic basis for resemblance between parents and offspring.

Heterozygous

Having different alleles for a given gene. An individual can be heterozygous for some genes and homozygous for others.

Heterozygosity

In a population, the average proportion of genes for which a randomly chosen individual is heterozygous.

Homozygous

Having two copies of the same allele for a given gene. An individual can be homozygous for some genes and heterozygous for others.

Mean

The arithmetic average of a set of values.

Macroevolution

Evolution across geologic timescales (generally millions of years), involving groups of species.

Microevolution

Evolution within a population, over shorter timescales than those examined in macroevolution.

Mutation

A change in the nucleotide sequence of a gene in an individual.

Natural Selection

One of several mechanisms that may drive evolution. Individuals that have traits that are favorable within their environment survive and reproduce more than those with less favorable traits, leading to the spread of those favorable traits.

Null Hypothesis

An assertion that there is no relationship among observations, that the relationship is due to chance, or that an experimental treatment has no significant effect.

Phenotype

the physical or morphological expression of a genotype in a given environment

Population

a group of interbreeding individuals that belong to the same species and occupy a similar geographic area

Population Genetics

an approach to understanding microevolution that combines mathematical theory and experimental data to understand the effects of mutation, genetic drift, gene flow, and natural selection on genes within and among populations

Allele frequencies

population of a specific allele (version of a gene) among all allele copies in a population

Genetic variation

diversity of gene frequencies

Hardy-Weinberg Principle

mathematical model stating that allele and genotype frequencies in a population will remain constant from generation to generation if no evolutionary forces are present; the null hypothesis for evolution

Speciation

evolutionary process by which populations evolve to become a distinct species

Dominant alleles

an allele that expresses its phenotype even when paired with a different allele

Recessive alleles

an allele that only expresses its phenotype when paired with an identical allele

Genotype frequencies

the proportion of each genotype (AA, Aa, aa) in a population

Inbreeding

mating between closely related individuals

Biological fitness

the ability of an individual to survive and produce fertile offspring relative to other individuals in the population

Nucleotide

the building blocks of DNA - adenine, thymine, guanine, cytosine

Ancestral

trait/state that was present in the common ancestor of the group

Character

heritable attribute of an organism (i.e. eye color)

Clade

monophyletic group - a group of organisms consisting of a common ancestor and all of its descendants

Cladogram

a diagram showing the branching sequence of evolutionary relationships

Convergence

the independent evolution of similar features in species of different lineages

DNA alignment

the processing of arranging DNA sequences to identify regions of similarity that may indicate evolutionary relationships

Fossil record

the total number of fossils discovered and the information derived from them

Homolog

a specific entity (gene, protein, anatomical feature) that shares a common ancestry

Homology

traits in different species that are similar because they were inherited from a common ancestor

Homoplasy

a character shared by a set of species but are not present in their common ancestor

Ingroup

the group of primary interest being studied in a phylogenetic analysis

Locus

the specific physical location of a gene or DNA sequence on a chromosome

Monophyletic group

a group of organisms consisting of a common ancestor and all its descendants

Morphology

the study of the form and structure of organisms

Outgroup

a distantly related taxon used as a reference point to determine the evolutionary direction of traits in the ingroup

Phylogenetic tree

a graphical representation of the evolutionary relationships among various species based on genetic or physical traits

Polarization

determining which character state is ancestral and which is derived

Reversal

an evolutionary change where a lineage returns to an ancestral character state

Sister taxa

two lineages that are each other's closest relatives

Synamorphology

a shared, derived character state that is unique to a particular clade and used to define that clade

Community

All populations of different species that live and interact in the same area

Ecosystem

A biological community of the biotic and abiotic environment

Biosphere

The global sum of all ecosystems on Earth

Life History

The schedule and duration of key events in an organism's lifetime - birth, growth, reproduction, death

Principle of Allocation

Energy used for one function (i.e. growth) is unavailable for other functions (i.e. defense or reproduction)

Trade Off

The evolutionary compromise where an increase in one beneficial trait leads to a decrease in another trait

Survivorship

The probability of individuals in a population surviving to various ages

Fast-slow continuum

Spectrum of life history strategies

Fast - r-selected

Mature early, many offspring, smaller, die earlier

Slow - k-selected

Mature late, few offspring, larger, die later

Birth

One of the four factors that change population size - BIDE

Death

One of the four factors that change population size - BIDE

Immigration

One of the four factors that change population size - BIDE

Emigration

One of the four factors that change population size - BIDE

B-D model

Basic model of population change assuming closed: Nt+1 = Nt + B - D

Exponential model

J curve - population growth at constant rate, assumption that resources are unlimited

Logistic model

S curve - population growth that slows as it reaches carrying capacity K

Per capita population growth rate

r - average contribution of each individual to population growth

Density dependence

When birth or death rate change as population density changes

Equilibrium population size

The point where population size stays constant - Births = deaths

Carrying capacity (K)

The maximum number of individuals an environment can support

Intrinsic growth rate (r)

The maximum potential growth rate of a population under ideal conditions

Population fluctuation

Variation in population size over time due to environmental changes or species interactions

Intraspecific competition

Competition within the same species

Interspecific competition

Competition between different species

Predation

The killing and consumption of another organism

Herbivory

An animal eats a plant organism

Parasitism

One species benefits and the other is harmed

Mutualism

Both species benefit

Commensalism

One species benefits and the other is unaffected

Facilitation

An interaction where at least one species benefits and neither is harmed

Defense

Adaptations to avoid being eaten

Dishonest mimicry

A harmless species mimics a dangerous species

Honest mimicry

Two dangerous species look alike

Exploitation competition

Indirect competition where species compete by consuming the same limited resource

Indirect mutualism

Two species benefit each other through a third party

Interaction network

A map of all interactions between species in an ecosystem

Coexistence

Two or more species live in the same habitat without one driving the others to extinction

Scarcity

Resources are in a short supply relative to the demand from the organisms in the community

Competition

Interaction between individuals or species in which fitness of one is lowered by the presence of another

Fundamental niche

The entire set of environmental conditions under which a species can survive and reproduce

Realized niche

The actual environment conditions a species does occupy after accounting for interactions