UNIT 7 AP BIOLOGY

Adaptation

Inherited characteristics of organisms that enhance their survival and reproduction in specific environments

Natural selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than do other individuals because of those traits, reason for life’s diversity

Descent with modification

Darwin’s idea that there is unity in life that is attributed to the descent of all organisms from an ancestor that lived in the remote past.

Artificial selection

Process by which humans have modified other species over many generations by selecting and breeding individuals that possess desired traits

Observation #1

Members of a population often vary in their inherited traits

Observation #2

All species can produce more offspring than their environment can support, and many of these offspring fail to survive and reproduce

Advantageous heritable traits in an organism

increase the number of offspring that survive and reproduce, so the traits that are favored likely appear at a greater frequency in the next generation, thus natural selection resulting from factors such as predation, lack of food, or adverse physical conditions can lead to an increase in the proportion of favorable traits in a population

Individuals do NOT evolve —

It is the population that evolves over time; natural selection can amplify or diminish only those heritable traits that differ among individuals in a population. Thus, even if a trait is heritable—if all the individuals in a population are genetically identical for that trait —evolution by natural selection cannot occur.

In species that produces new generations in short periods of time,

evolution by natural selection can occur rapidly

Natural selection depends on time and place

It favors characteristics in a genetically variable population that provide an advantage in the current local population.

Homology

Similarity from a common ancestry—related species can have characteristics that have an underlying similarity yet function differently.

Vestigial structures

Remnants of features that served a function in the organism’s ancestors

Biogeography

The scientific study of geographic distributions of species

Endemic

Found nowhere else in the world — explains why 2 islands with similar environments in distant parts of the world tend not to be populated by species that are closely related to each other, but rather species related to those of the nearest mainland.

Some heritable phenotypic differences occur on an “either-or” basis

Typically determined by a single gene locus and other phenotypic graduations along a continuum due to the influence of 2 or more genes on a single phenotypic character.

Genetic variation at the whole gene level (gene variability) can be quantified as

the average percentage of loci that are heterozygous

Heterozygous

2 different alleles for given locus

Homozygous

2 identical alleles for given locus

Genetic variation can also be measured by

nucleotide variability, but little of this variation results in phenotypic variation b/c most nucleotide variations occur within introns — noncoding segments of DNA lying between exons, the regions retained in mRNA after RNA processing

Of the variations that occur within exons,

most do not cause a change in the amino acid sequence of the protein encoded by the gene and some phenotypic variation does not result from genetic differences among individuals.

Phenotype

The product of an inherited genotype and many environmental influences, only the genetically determined part of phenotypic variation can have evolutionary consequences

Sources of genetic variation include

mutation, gene duplication or other processes produce alleles and new genes, sexual reproduction with rearrangement of pre-existing genes

New alleles can arise by mutation

A change in the nucleotide sequence of an organism’s DNA, caused by errors in DNA replication, exposure to UV light, and high energy forms of radiation, and exposure to certain chemicals

Point mutation in noncoding regions generally result in

neutral variation, differences in DNA sequence that do NOT confer an advantage or selective disadvantage

Even a point mutation (a change as a little as one nucleotide base in a gene) that encodes a protein will have

no effect on the protein’s function if the amino acid composition is not changed

Even when there is a change in the amino acid, it may not affect the protein’s shape and function

In multicellular organisms, only mutations in cell lines that produce gametes can be

passed to off-spring

Chromosomal changes that delete or disrupt or rearrange many loci are usually

harmful, when large scale changes leave genes in fact, they may not affect organisms phenotype (some are beneficial ex. the translocational of one chromosome to a different chromosome could link genes in a way that produces a positive effect)

Gene duplication that does not have severe effects can

persist over generations, allowing mutations to accumulate and lead to an expanded genome with genes that may take on new functions

Rapid reproduction

Mutations can quickly generate genetic variation in populations that have many more reproductions in 1 unit of time

Sexual reproduction

Genetic variation in a population results from the unique combination of alleles that each individual receives from its parents

At the nucleotide level, sexual reproduction shuffles existing alleles and deals them at random to produce individual genotypes

3 mechanisms contribute to gene shuffling

1. Crossing over independent assortment of chromosomes and fertilization

2. During meiosis, homologous chromosomes, one from each parent trade some of their alleles

3. Homologous chromosomes and alleles they carry are then distributed at random into gametes

A deviation from new mutations can

alter allele frequencies, but because mutations are rare, the change from one generation to the next is likely to be very small

Nonrandom mating

can affect the frequencies of homozygous and heterozygous genotypes, but by itself has no allele frequencies in the gene pool

Allele frequencies can

change if individuals with certain inherited traits are more likely than other individuals to obtain mates—violates random mating and no natural selection

By consistently favoring some alleles over others, natural selection can

cause adaptive evolution, a process in which traits that enhance survival or reproduction tend to increase in frequency over time. Chance events can also cause allele frequencies to fluctuate unpredictably from one generation to the next known as genetic drift

Genetic drift is significant in

small populations, causes allele frequencies to change at random, can lead to a loss of genetic variation within populations and can cause harmful alleles to be fixed since survival of population can be threatened

Relative fitness

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

Directional selection

When conditions favor individuals exhibiting one extreme of a phenotypic range, thereby shifting a population’s frequency curve for the phenotypic character in one direction or the other.

Disruptive selection

When conditions favor individuals at both extremes of a phenotypic range over individuals with intermediate phenotypes

Stabilizing selection

Acts against both extreme phenotype and favors intermediate variants

Balancing selection

Type of selection includes heterozygote advantage and frequency-dependent selection

Binomial

The two part format of the latin scientific name for an organism where the first part is the genus and the second part is the specific epithet which is unique for each species in the genus where species that appear to be closely related are grouped into the same genus.

The Linnaean system

Places related genera into the same family, families into orders, orders into classes, classes into phyla, phyla into kingdoms, kingdoms into domains

Taxon

The named taxonomic unit at any level of the hierarchy is called a taxon

Branch points

Represent the common ancestor of the two evolutionary lineages diverging from it

Evolutionary lineage

A sequence of ancestral organisms leading to a particular descendant

Sister taxa

groups of organisms that share an immediate common ancestor that is not shared by any other group

members of a sister group are each other’s closest relatives

Rooted trees

A branch point within the tree represents the most recent common ancestor of all taxa in the tree

Basal taxon

A lineage that diverges from all other members of its group early in the history of the group

High degree of gene sequence similarity indicates

they are closely related + vice versa

Clades

groups that species are placed in

A taxon is only equivalent to a clade only if it is

monophyletic, signifying that it consists of an ancestral species and all of its descendants

Paraphyletic groups

Consist of an ancestral species and some but not all of its descendants

Polyphyletic groups

include distantly related species but does not include most recent common ancestor

Shared ancestral character

A character that originated in an ancestor of the taxon

Shared derived character

An evolutionary novelty unique to a clade

Outgroup

Species or a group of species from an evolutionary lineage that is closely related to but not part of the group of species we are studying (the ingroup)

The principle of maximum parsimony

Simplest explanation should first be investigated that is consistent with the facts or fewest evolutionary events

Phylogenetic bracketing

Predicting by parsimony that features shared by two groups of closely related organisms are present in their common ancestor and all of its descendants unless independent data indicates otherwise.

Molecular clock

An approach for measuring the absolute time of evolutionary change based on the observation that some genes and other regions of genomes apear to evolve at constant rates.

Mutation

Random change in an organism’s genome

Provides new phenotypes that contribute to evolution by natural selection

Genetic Drift

The random change in the frequency of a particular allele within a population

Nonselective process generally occurring in small populations, increased death rates and low reproductive rates, natural catastrophes

Bottleneck events can contribute to

genetic drift — a large, diverse population suddenly reduced to small population

Founder effect

Refers to a random process that reduces genetic variation within a small population due to a separation from a larger population, migration and geological events, genetic makeup can be different from the original population

Migration/Gene Flow

Movement of individuals between populations causes an exchange of alleles between populations, causing an exchange of alleles between populations

Introduces new genes into populations, increases genetic variation

Continued migration between populations reduces genetic diversity between populations over time

Null Hypothesis

Hypothesis which states experimental variables have no relationship and experimental observations are the result of choice

Alternative Hypothesis

One of several hypotheses stating that experimental variables have a relationship and the experimental observations are the result of some nonrandom cause

Evidence of Evolution

Geographical (habitat, land area), geological (fossils), physical (phenotypes), biochemical, morphological (shared modified traits)

Homologous structures

Variation in a structure that was present in a common ancestor

Analogous structures

Evolved independently in different species due to similar environmental/selective pressures

More amino acid differences,

the more time that has passed since the divergence

Membrane-bound organelles are structural evidence for common ancestry of all eukaryotes

Double membrane, circular genomes, ribosomes, endosymbiotic theory, linear chromosomes

Prokaryotic genomes

Single circular chromosomes, cytoplasm, genomes are small, introns

Mechanisms of genetic change:

Changes in DNA (gene, chromosomal mutations), cell division (sexual reproduction, independent assortment, crossing over), and environmental disruptions

Transition fossils

As one group evolves into another, shows evolutionary changes

Frequency of resistance

can increase within populations, usually comes from mutation and trait provides better fitness

Speciation

Refers to the creation of new species and life’s diversity, which occurs when populations are reproductively isolated

Reproductive isolation prevents gene flow between populations

Species

Defined as a group capable of interbreeding and exchanging genetic information to produce viable, fertile offspring

Biological barriers keep members of 2 different species from

1. Interbreeding

2. Producing fertile offspring

Habitat isolation (Prezygotic barrier)

Species occupy different habitats and rarely come in contact

Temporal isolation (Prezygotic barrier)

Species breed during different times of day, seasons or years.

Behavioral isolation (Prezygotic barrier)

Species have different courtship behaviors or mate preferences

Mechanical isolation (Prezygotic barrier)

Reproductive structural differences prevent successful mating and reproduction

Gamete isolation (Prezygotic isolation)

Sperm of one species may not be able to fertilize the eggs of another species

Hybrid inviability (Postzygotic barrier)

Mating results in a zygote, but incompatibility may stop the development of the zygote

Hybrid sterility

The offspring hybrid produced is vigorous, but may be sterile (Donkey and Horse ex.)

Hybrid breakdown

First generation hybrids are viable and fertile, but resulting generations are feeble and sterile.

Allopatric isolation

Geographically isolated; no gene flow and different selection pressures

Sympatric speciation

Evolution of a new species due to individuals being reproductively isolated from surviving ancestral population (Genetic mutation such as polyploidy, habitat differences, sexual selection), SAME GEOGRAPHIC AREA

Punctuated equilibrium

Evolution occurs rapidly after a long period of stasis (little to no change)

Gradualism

Evolution occurs slowly over hundreds of thousands or millions of years

Adaptive Radiation

Refers to the evolution of new species that allow empty ecological roles or niches to be filled, speciation rates are more rapid since new habitats become available

Similar selection pressures result in

similar phenotypic adaptations

Convergent evolution

Process by which similar environmental conditions select for similar traits in different populations or different species over time

Convergence in phenotype is usually observed in organisms that are distantly related but are adapted to similar niches

Populations with little genetic diversity are

at risk of extinction

Diverse population

Species with a variety of adaptations are more likely to contain individuals who can withstand new environmental pressures

Deleterious traits

are those that reduces the chance of survival

Adaptive traits

Those that increase chances of survival

Extinction

Disappearance of species such that no future generations will naturally populate the Earth, can be rapid during times of ecological stress; extinction provides niches for other species

RNA World Hypothesis

RNA could have been the the earliest genetic molecule serving a role similar to amino acids/proteins and DNA

Early earth conditions were ideal for forming monomers for life