BIO 220 EXAM 1 VOCAB

Homology

Similarity of characteristics resulting from shared ancestry

A Homologous Characteristic…

Is similar in two or more species because it is inherited from a common ancestor

Descent with Modification

Passing of traits from parents to offspring. (accounts for gradual change in species’ traits and homology

Natural Selection

A mechanism that can lead to adaptive evolution. (Different phenotypes lead to different fitness)

Artificial Selection

Selective breeding of animals and plants to encourage the occurrence of desirable traits.

Adaptation

Inherited aspect of an individual that allows it to outcompete other members of the same population that lack the trait.

DNA

Double-stranded molecule containing genetic information for development, life and reproduction.

Genetic Drift

Evolution arising from random changes in the genetic composition of a population from one generation to the next.

Bacteria

One of the two prokaryotic domains of life.

Archaea

One of the two prokaryotic domains of life, distinguished by biochemical features.

Eukarya

Membrane-enclosed cell nuclei and mitochrondria.

Nucleotide

Structural unit that links together to form DNA & RNA

Base

One of the four nitrogen-containing molecules (in DNA/RNA)

Mutation

Change to the genomic sequence of an organism

Ploidy

Number of copies of unique chromosomes in a cell.

S-x Chromosome

Pairs during meiosis but differs in copy number between males and females.

Autosome

Chromosome that doesn’t differ between sexes

Pseudogene

DNA Sequence that resembles a functional gene but has lost its protein-coding ability or is no longer expressed. (Form after gene has been duplicated.)

Somatic Mutation

Affects the cells in the body of an organism.

Germline Mutation

Affects the gametes of an individual and can be transmitted from parents to offspring.

Allele

One of any number of alternative forms of the DNA sequence of the same locus.

Meiosis

Occurs only in eukaryotes, form of cell division that cuts the number of chromosomes in half.

Genetic Recombination

Exchange of genetic material between paired chromosomes during meiosis.

Independent Assortment

Random mixing of maternal and paternal copies of each chromosome during meiosis. (leads to genetically unique gametes)

Genotype

Genetic makeup of an individual.

Phenotype

Observable, measurable characteristic of an organism.

Genetic Polymorphism

Each phenotype results from a different allele or combination of alleles of a single gene.

Polyphenism

Trait for which multiple, discrete phenotypes can arise from a single genotype depending on environmental circumstances.

Morphogen

Signaling molecule that flows between nearby cells and acts directly to alter the expression of target genes.

Phenotypic Plasticity

Changes in the phenotype produced by a single genotype in different environments.

Population Genetics

Study of the distribution of alleles within populations and the mechanisms that can cause allele frequencies to change over time.

Genetic Locus

Specific location of a gene or piece of DNA sequence on a chromosome.

Null Hypothesis

Default hypothesis that there is no relationship between two measured phenomena.

Fixed

Allele that remains in a population when all of the alternative alleles have disappeared.

Genetic Bottleneck

Event in which the number of individuals in a population is reduced drastically.

Founder Effect

Form of genetic drift. Loss of allelic variation that accompanies the founding of a new population from a very small number of individuals.

Fitness

Success of an organism at surviving and reproducing and thus contributing offspring to future generations.

Relative Fitness

Success of the genotype at producing new individuals standardized by the success of other genotypes in the population.

Average Excess of Fitness

Difference between the average fitness of individuals bearing the allele and the average fitness of the population as a whole.

Pleiotropy

Condition when a mutation in a single gene affects the expression of more than one different phenotypic trait.

Antagonistic Pleiotropy

When a mutation with beneficial effects for one trait also causes detrimental effects on other traits.

Negative Selection

Selection that decreases the frequency of alleles within a population. (Average excess for fitness of an allele is less than zero.)

Positive Selection

Selection that increases allele frequency in a population. (Average excess for fitness of an allele is more than zero.)

Epistasis

Effects of an allele at one genetic locus are modified by alleles at one or more other loci.

Additive

Allele that yields twice the phenotypic effect when two copies are present at a given locus than occurs when only one copy is present. (Not influenced by presence of other alleles.)

Negative Frequency-Dependent Selection

Takes place when rare genotypes have higher fitness than common genotypes. (Maintain genetic variation within populations.)

Heterozygote Advantage

Selection favors heterozygote individuals over either the dominant/recessive homozygote.

Balancing Selection

Type of selection that favors more than one allele. Process acts to maintain genetic diversity in a population by keeping alleles at frequencies higher than would be expected by chance or mutation alone.

Inbreeding Coefficient (F)

The probability that two alleles at any locus in an individual will be identical because of common descent.

Inbreeding Depression

Reduction in the average fitness of inbred individuals relative to that of outbred individuals. (Arises because rare alleles become expressed in a homozygous state where they can affect detrimentally the performance of individuals.)

Genetic distance

Measure of how different populations are from each other genetically.

Gene Flow

Movement, or migration, of alleles from one population to another.

Hardy-Weinberg Theorem

Describes how allele and genotype frequencies remain constant in a population under specific conditions. (No mutation, migration, selection, genetic drift, non-random mating.)

△p (variable)

Change in allele frequency.

p (variable)

Frequency of allele.

w (with line over it) (variable)

Fitness average of population.

a (variable)

Average excess of fitness for allele.

△q (variable)

Change in allele frequency from one generation to the next, due to mutation will be.

μ (variable)

Rate to which mutation converts.

Variance Equation

Vp = Vg + Ve

Heritability

Proportion of total phenotypic variation that is attributable to genetic variation among individuals.

Broad-sense Heritability (H²)

Proportion of the total phenotypic variance of a trait because of genetic variance.

H² equation

Vg / Vg+Ve

Narrow-sense Heritability (h²)

Proportion of the total phenotypic variance of a trait because of the additive effects of alleles. (Ability to transmit phenotypic characteristics to offspring.)

h² equation

Va / Va + Vd + Vi + Ve

Va

Additive genetic variance.

Vd

Variance due to dominance affect alleles.

Vi

Variance due to epistatic interactions.

Ve

Variance due to environment.

Breeder’s Equation

R = h² x S

Directional Selection

Favors individuals on one end of the distribution of phenotypes present in a population.

Stabilizing Selection

Favors individuals in the middle of the distribution of phenotypes present in a population.

Disruptive Selection

Favors individuals at the tails of the distribution of phenotypes present in a population.

R

Evolutionary Response

S

Phenotypic variation that influences fitness.

Linkage Equilibrium

Exists for any two loci if the occurrence of an allele at one of the loci is independent of the presence/absence of an allele at the other locus.

Linkage Disequilibrium

Exists for any two loci if the occurrence of an allele at one of the loci is nonrandomly associated with the presence/absence of an allele at the other locus.

Physical Linkage

Adjacency of two or more loci on the same chromosome.

Supergenes

Group of functionally related genes located close enough together that they segregate as a single unit.

Quantitative trait locus (QTL)

Stretch of DNA that is correlated with variation in a phenotypic trait.

Genome-wide association (GWA)

Mapping involves scanning through the genomes of many different individuals, some with, and others without, a focal trait of interest, to search for markers associated with expression of the trait.

Phenotypic Plasticity

Changes in the phenotype produced by a single genotype in different environments.

Branch

Lineage evolving through time that connects successive speciation or other branching events.

Phylogeny

Visual representation of the evolutionary history of populations, genes, or species.

Node

Point in a phylogeny where a lineage splits.

Tip

Terminal end of an evolutionary tree.

Internal Node

Node that occurs within a phylogeny and represents ancestral populations or species.

Clade

Single “branch” in the tree of life; each one represents an organism and all of its descendants.

Taxon

Group of organisms that a taxonomist judges to be a cohesive taxonomic unit, such as a species or order.

Monophyletic

Group is made up of an organism and all of its descendants.

Polyphyletic

Taxonomic group that does not share an immediate common ancestor and therefore does not form a clade.

Paraphyletic

A group of organisms that share a common ancestor, although the group does not include all the descendants of that common ancestor.

Character

Heritable aspect of organisms that can be compared across taxa.

Synapomorphy

Derived form of a trait that is shared by a group of related species.

Outgroup

Group of organisms (for example, a species) that is outside of the monophyletic group being considered.

Homoplasy

Describes a character state similarity not due to shared descent.

Convergent Evolution

Independent origin of similar traits in separate evolutionary lineages.

Evolutionary Reversal

Reversion of a derived character state to a form resembling its ancestral state.

Parsimony

Principle that guides the selection of the most compelling hypothesis among several choices.

Polytomy

Internal node of a phylogeny with more than two branches