biology unit 2 review

speciation

the process by which one species splits into two species; produced the tremendous diversity of life

species

a group of populations whose members have the potential to interbreed in nature

reproductive isolation

the existence of biological factors that impede members of two species from interbreeding and produce viable, fertile offspring

hybrids

offspring that result from an interspecific mating

prezygotic barriers

barriers before the zygote that block fertilization from occurring

habitat isolation

a prezygotic barrier where a lack of opportunities to encounter one another prevents breeding; eg. snakes

temporal isolation

a prezygotic barrier where organisms breed at different times or seasons; eg. skunks

behavioral isolation

a prezygotic barrier where there are different courtship rituals; eg. bird calls

mechanical isolation

a prezygotic barrier where there is physical incompatibility of reproductive parts; eg. left-coiled snakes

gametic isolation

a prezygotic barrier where there is molecular incompatibility of eggs and sperm; eg. purple/red sea urchins

postzygotic barriers

barriers that occur after the hybrid zygote is formed

reduced hybrid viability

a postzygotic barrier where hybrid development is impaired by interaction of potential genes; eg. fragile salamander offpring

reduced hybrid fertility

a postzygotic barrier between vigorous hybrids that cannot produce viable offspring; eg. mules

hybrid breakdown

a postzygotic barrier where viable and fertile hybrids always produce sterile offspring; eg. horse and donkeys

morphological species concept

distinguishes a species based on observable physical traits

ecological species concept

defines a species in terms of its ecological niche

biological species concept

defines a specific group of populations whose members have the potential to interbreed in nature and produce fertile offspring

allopatric speciation

the formation of new species when physical geographic barriers separate a single population into isolated groups; gene flow is interrupted, and it is formidable depending on an organism’s ability to freely move about

sympatric speciation

when speciation occurs in populations that live in the same geographic area; less common than allopatric speciation, but it occurs when gene flow is reduced by such factors as polyploidy, sexual selection, and habitat differentiation

perpatric speciation

a type of evolutionary process when a new species forms from a small, isolated population located at the outer edge of a large parent population

autopolyploidy

genetic condition when an organism has three or more complete sets of chromosomes that all originate from the same species

allopolyploidy

a genetic condition where an organism possesses three or more sets of chromosomes derived from at least two species

hybrid zone

a region in which members of different species meet and mate, producing at least some offspring of mixed ancestry

reinforcement

a process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing chance of hybrid formation (only occurs if offspring hybrid are less fit than members)

fusion

when successful matings and high gene flow may reverse the speciation process, causing the two hybridizing species to fuse into one

stability

when many hybrid zones are fairly stable and the production of hybrids allows for some gene flow, but the species remains isolated

the four main stages for which chemical and physical processes could have produced simple cells

1. the abiotic synthesis of small organic molecules, such as amino acids and nucleotides

2. the joining of small molecules into macromolecules, such as proteins and nucleic acids (polymers)

3. the packaging of small molecules into protocells (molecules with water loving and water avoiding ends that can form bilayers and reside spontaneously)

   1. the origin of self replicating molecules that eventually made inheritance possible

Miller experiments

simulated early Earth’s atmosphere and oceans to see if organic building blocks could form naturally from inorganic molecules; proved that abiotic synthesis of organic molecules is possible

stromatolites

layered rocks that form when prokaryotes bind thin films of sediment together

endosymbiosis

a relationship between two species in which one organism lives inside the cell of another organism

serial endosymbiosis

a hypothesis that suggests that mitochondria evolved before plastids through a sequence of endosymbiotic events

cambrian explosion

when many present-day animals suddenly appeared in fossils formed 535 million years ago

plate tectonic theory

states that Earth’s solid outer layer is broken into massive moving pieces that float on a hotter, softer layer beneath

mass extinction

when large species become extinct worldwide, causing ecological niches and diversification

adaptive radiations

periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their community

heterochrony

an evolutionary change in the rate or timing of developmental events in an organism compared to its ancestors

homeotic genes

determine basic features as where a pair of wings and legs develop on a bird

oxygenic photosynthesis

biological process where organisms use light energy to convert water and carbon dioxide into sugars and molecular oxygen

karyogenic hypothesis

an evolutionary theory that proposes the cell nucleus and its surrounding nuclear envelope gradually formed entirely within an ancestral prokaryotic cell lineage without the involvement of an endosymbiotic event

endokaryotic hypothesis

an evolutionary theory proposing that the cell nucleus of eukaryotes originated from an endosymbiotic event

phylogenetic tree

represents a hypothesis about evolutionary relationships between taxa; each branch point represents the divergence of two evolutionary lineages from ancestor; allows us to predict features of an ancestor from features of descendants

sister taxa

groups that share an intermediate common ancestor not shared by anyone else; humans and chimps for example

phylogeny

the evolutionary history of a species or group of related species

systematics

classifies organisms and determines their evolutionary relationships

rooted tree

includes a branch to represent the most recent common ancestor of all taxa in the trees

basal taxon

diverges early in the history of a group and originates near the common ancestor of the group; eg. fishes and frogs w/ the four limbs

homoplasy

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

cladistics

groups organisms by common ancestry

paraphyletic grouping

a biological grouping that includes a single common ancestor and some, but not all, of its descendant lineages

polophyletic grouping

a collection of organisms that share similar physical traits but do not share a common ancestor

monophyletic grouping

a group that consists of a single common ancestor and all of its descendants

distance analysis

calculates the pairwise distance between sequence (how similar/different they are)

maximum parsimony

a method used in biology to build phylogenetic trees by finding the evolutionary tree that requires the smallest number of changes, such as genetic mutations

orthologous genes

genes in different species that evolved from a common ancestral gene through a speciation event

paralogous genes

genes within a genome that share a common ancestor and separated because of a gene duplication event

gene duplication

increases the number of genes in the genome, proviidng more opportunities for evolutionary changes

molecular clock

uses constant rates of evolution in some genes to estimate the absolute time of evolutionary change

in orthologous genes: nucleotide substitutions are assumed to be proportional to the time since they last shared a common ancestor

in paralogous genes: nucleotide substitutions are assumed to be proportional to the time since genes duplicated

homology

phenotypic and genetic similarities due to shared ancestry

analogy

a similarity due to convergent evolution

horizontal gene transfer

the movement of genes from one gene to another by means of plasmids, viral infections, etc. plays a key role in the evolution of both prokaryotes and eukaryotes. explains why different genes produce different trees of life

what is an example of horizontal gene transfer?

5% of alga genes are from archaea as a result of horizontal gene transfer

characteristics of prokaryotes

microscopic, but what they lack in size they make up for in numbers. an example of this is Yellowstone; the vivid red/orange/yellow rings are colonies of prokaryotes. two main domains are archaea and bacteria.

why are prokaryotes essential?

they recycle carbon/nitrogen/almost every chemical element. bacterial cells on the human body produce important vitamins.

most common shapes of prokaryotes

spherical (cocci), rod-shaped (bacilli), spiral (spirilla)

gram positive bacteria characteristics

have relatively simple walls composed of a thick layer of peptidoglycan. stains purple. contain endospores.

gram negative bacteria characteristics

bacteria have less peptidoglycan and are structurally more complex. they are usually more resistant than gram positive species to antibiotics because they have glycocalyx, a sticky layer of polysaccharide or protein and an outer membrane containing lipopolysaccharide.

endospores

short hair-like protein appendages found on the surfaces of many bacteria that help them attach to surfaces

pili

tiny hair-like structures found on the surface of many bacteria