bio unit 7

niche

role or function of an organism or species in an environment

requirements for natural selection to occur

competition, variation, adaptation, heritability

homologies

similarities between species due to common ancestry

homologous structures

same structure, different function

vestigial structure

once served important functions but have lost function

analogous structures

different structures, same function

convergent evolution

organisms become similar due to similar environments

comparative embryology

similar structures not visible in adult organisms

genetic drift

allele frequencies change by random chance; significant in small populations, can lead to loss of genetic variation

founder effect

few individuals become isolate and start a new population

bottleneck effect

drastic reduction in population due to environmental change

gene flow

movement of alleles into or out of the population

adaptive evolution

increase in frequency of alleles that improve fitness

directional selection

favor individuals at one end of phenotypic range

disruptive selection

favor individuals at both extremes of phenotypic range

stabilizing selection

favor intermediate variants and act against extreme phenotypes

heterozygote advantage

heterozygotes have a higher fitness than both homozygotes

reproductive isolation

biologic barriers that stop two species from producing viable fertile offspring

prezygotic barriers

impede mating, hinder fertilization if mating is successful

postzygotic barriers

prevents fertilized egg from developing into a viable fertile adult

reduced hybrid viability

genes of different parents impair hybrid development and survival

reduced hybrid fertility

sterile

hybrid breakdown

first generation hybrids are fertile, but when they mate with another species or with parent species, the offspring of the next generation is weak or sterile

speciation

one species splits into two or more (reproductive isolation is the driving force)

allopatric speciation

geneflow interrupted when population is divided into geographically isolated subpopulations

sympatric speciation

geneflow reduced between groups in a population that are still in contact

polyploid

presence of extra sets of chromosomes

maximum parsimony

tree that requires the fewest evolutionary events is the most likely to be the best tree

how did life start on earth

1. abiotic synthesis of small organic molecules

2. joining of these molecules into macromolecules

3. packaging of molecules into protocells

4. origin of self replicating molecules

stanleymiller and haroldurey

showed that abiotic synthesis in a reducing atmosphere is possible

protocells

fluid filled vesicles; replication and metabolism may have appeared together in these

rna world hypothesis

first genetic material was probably rna; provided the template for the evolution of dna

anaerobic prokaryotes and cyanobacteria

dominated early earth when oxygen levels were low

adaptive radiation

quick evolution of many diversely adapted species from a common ancestor (follows mass extinction, evolution of new characteristics)