chapter 22- systematics

What is the value of classifying organisms?

a natural human tendency

What is a phylogeny?

scientific classification based on evolutionary relationships

What is systematics?

the science of classifying organisms based on evolutionary

relationships

How does a phylogenetic tree represent evolutionary relationships?

grouping organisms that are most closely related evolutionarily; show patterns of shared ancestry

What is a taxon?

a specific group (ex: domain, kingdom, phylum, class, order, family)

What is the root of an evolutionary tree?

base of phylogenetic tree; represents distant common ancestor of all members of the tree

What do nodes on a phylogenetic tree represent?

point where two evolutionary lineages diverge from their common

ancestor

What are sister taxa?

two lineages stemming from the same branch point; taxa that are most closely related

What is a polytomy?

an unresolved branching point

Why would a phylogenetic tree contain a polytomy?

a branching point where the exact relationships are unknown

What is a character?

heritable trait possessed by an organism

What is a character state?

the specific expression of the character in the taxon

What are apomorphic characters?

species that share these characters are believed to do so because they

share a more recent common ancestry

What are plesiomorphic characters?

species share this characteristic because they shared it with a distant

ancestor; doesn’t necessarily imply recent shared ancestry; evolutionary remnants of a distant shared ancestry

Which characters (apomorphic or plesiomorphic) are more phylogenetically informative?

apomorphic

What are homologous characters?

same origin, different function

What are analogous characters?

same function, different origin

What does it mean to say that something is phylogenetically informative?

they are more likely to have a common ancestor

Which is more phylogenetically informative, homologous or analogous characters?

homologous

How is molecular or genetic data used as a phylogenetic character?

shared biochemical pathways (enzymes) can be evidence of evolutionary relationships; shared gene sequences can be evidence of evolutionary relationships

What is homoplasy?

character states shared but no arising from a common ancestor; can be evidence of convergent evolution

What is a reversal?

a shared characteristic can be evolved and then lost in a taxon

Why would homoplasy and reversal make determining phylogenetic relationships difficult?

can make identification of shared character states difficult

How do systematists resolve these problems of having so many characters to analyze?

Horizontal Gene Transfer

What does it mean when phylogenetic patterns are concordant?

some taxa appear to be derived from more than one ancestral taxon

What is parsimony?

the simplest/ fewest evolutionary changes

What was the traditional (Darwinian) view of the evolutionary tree?

species are ever diverging; one species splits into two, new species split off that some lineages go extinct

What is monophyletic evolution?

What is polyphyletic evolution?

Why does polyphyly make resolving phylogenies more difficult?

when faced with many possible explanations of how a group of organisms evolved and are related, the simplest explanation (least steps) is the most likely

What is horizontal gene transfer?

two species with shared genes traditionally assumed to have evolved those genes from a common ancestor

Why does HGT complicate making phylogenies?

transferring genetic material between unrelated species, causing different genes within a genome to have distinct evolutionary history

Which types of organisms are most susceptible to horizontal gene transfer?

prokaryotes