Flashcards in Oct 18 Deck (41):
The sphynx (hairless) and tabby (haired) cats are more closely related than the tabby cat and bobcat. Therefore, the hair trait is
Which DNA substitution model weights transversions and transitions differently?
Bootstrapping provides confidence about
a) how the data supports the inferred tree
b) accuracy of the evolutionary history
a) how the data supports the inferred tree
What do species trees do?
recover the historical patterns of descent for populations, species, genera, etc.
What do gene trees do?
reflect the evolutionary history of a single locus
Gene trees and species trees are always congruent
Essential genes evolve/acquire mutations (slowly/quickly)
What does the 16S rRNA gene do?
essential for the catalytic functions of the ribosome
Evolutionary trajectory of essential or highly conserved genes often parallels that of their host species
What are 3 examples of horizontal gene transfer?
-conjugation in bacteria (antibiotic resistance)
-hybridization between closely related species
What phenomenon makes it difficult to construct phylogenies?
horizontal gene transfer
What is the evolutionary species concept?
Species are populations with a shared evolutionary history and fate
What is the phenetic species concept?
delimits species based on shared traits
What is a challenge in the phenetic species concept?
Which traits to look at?
What is the biological species concept?
delimits species based on populations capable of interbreeding
What defines evolutionary fate in the biological species concept?
What is the phylogenetic species concept?
delimits species by resolving the smallest monophyletic clade with members uniquely sharing the derived traits
Does the phylogenetic species concept have inherent taxonomic hierarchy?
What do distinct evolutionary histories imply in the phylogenetic species concept?
lack of gene flow
In the phylogenetic species concept species delimitations may change if...
unanticipated gene flow occurs
What is allopatric speciation?
Reproductive incompatibility occurs in physically separated populations-->genetic drift, accumulation of mutations and natural selection cause populations to diverge as different alleles are fixed within them
The dumbbell model describes...
geographic isolation-->reproductive isolation
The peripheral isolate model describes...
dispersal to isolated region
What is parapatric speciation?
1) gradient or cline causes adjacent populations to experience different selective conditions
2) but the populations can still mate, generating hybrids
3) Hybrids may lack traits that facilitate success in any part of the cline, causing them to be outcompeted by nonhybrids
What does bounded hybrid superiority suggest?
hybrids occupying the hybrid zone harbor unique traits exclusive of the progenitors that make them well-suited to environmental conditions not found in either extreme of the cline
What is sympatric speciation?
speciation in the absence of abiotic/biotic barriers
Two genetically related cichlids arose in a small, young lake with no obvious barriers between these species to prevent gene flow. Diet appeared to drive the divergence as each species was well-adapted to their habitats and preferred within-species mating, driving fixation of divergent alleles. This is an example of what type of speciation?
Reduced gene flow between apple maggots that feed on different host trees is an example of what type of speciation?
What are 3 parts of sympatric speciation?
1) no physical or spatial barriers
2) requires an instantaneous mechanism
3) niche partitioning (subsets specialize on particular resource) and adaptive radiation
What is character displacement?
Selection acts to exaggerate differences between sympatric species and thus reduces direct competition
Why don't species merge? What is the underlying assumption?
Reproductive character displacement will favor conspecific mating over hybrid mating; assumes reduced hybrid fitness
Behavioral, temporal, and habitat are what type of reproductive isolation?
Prezygotic isolating mechanisms
Zygote in viability, sterile hybrids, and sterile backcrosses are what type of reproductive isolation?
Postzygotic isolating mechanisms
What is the difference btw prezygotic and postzygotic isolating mechanisms?
Prezygotic isolating mechanisms prevent mating or successful fertilization between different species
Postzygotic isolating mechanisms affect zygote/embryo survival
What is ploidy?
Change in chromosome number
What are problems of ploidy?
-meiosis can go awry
-hybrids may survive but they are sterile
What is a problem of chromosomal rearrangement?
dysfunctional gametes (extra or no copies of important genes are passed on)-->unfit hybrid
What are 2 causes of reproductive isolation?
What is Dobzhansky-Muller incompatibility?
negative epistasis btw alleles in heterozygotes (hybrids)
What is heterogametic sex?
sex chromosomes are not the same ie. males