Lecture 11 Flashcards

1
Q

Homology

A
  • same structure shared by descendants of a common ancestor no matter how modified in descendent form
  • important to evolution because we need to know if something we’re studying is related to something we already know
  • comparision is vital–>is it the same thing?
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2
Q

Analogs

A
  • features that rose independently but look similar and don’t share a common ancestor
  • convergence/parallel evolution
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3
Q

Descent with modification

A
  • descendants from same ancestor but results in branching pattern due to modification
  • relates to characterization of homology (key idea)
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4
Q

Homology vs. Analogy

A
  • analogous structures have same function but aren’t evolutionarily linked (wings of fly and wings of airplane)
  • homologous structures are highly conserved (forelimbs of vertebrates-same components or horns of antelopes-all very divers in structure but descendants of primitive horns)
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5
Q

Evolutionary studies

A
  • most based on homologous structures
  • asking about think you can show to your satisfaction that they’re homologues.
  • can start looking at new things including loss of elements, and changes for new function
  • homology concept is used to trace evolution of homologous structures, including loss of element, or changes for new functions
  • aids in identifying analogs in evolution
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6
Q

Vertebrate forelimbs (birds)

A
  • much different in structure but same components
  • highly specialized for their function-know it’s doing something different, but you can’t see it.
  • trace back history of bird forewing limb to an animal that has a different more basal structure as compared to that of the other vertebrates
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7
Q

Levels of homology

A
  • can be homologous at one level and analogous at the next

- bats and bird’s forelimbs are homologous but not at the level of wings those are analogous

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8
Q

Artiodactyla

A
  • started out with 5 digits but reduced to walking on 4
  • then reduced in size to two
  • lightweight running structure achieved
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9
Q

Horses

A
  • have one digit that evolved from 5
  • went through stage of having three toes
  • reduces weight of foot for running
  • forelimbs are homologous but single toe is analog
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10
Q

Criteria for homology

A
  • shared spatial relationships in an anatomical system
  • composition and properties of the structure
  • historical continuity in evolutionary record (can you see earlier precursor, and earlier precursor of that?)
  • e.g. vertebrate skull
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11
Q

Vertebrate skull

A
  • in evolution skulls of some bones lost, some bones fused together, and some adopted new function
  • evolutionary trend you usually see: starts out complex, full of smaller bits that are eventually slimmed down to fewer components like in the case of the dog skull
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12
Q

Jaw bone

A
  • used to articulate behind the ear but now it articulates just in front of your ear
  • the bones that used to be the jaw articulation that now no longer had a job were incorporated into the hearing apparatus (incus and malleus)
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13
Q

Non-homology (homoplasy)

A
  • convergence can produce similar solutions which can be considered false homologies–>homoplasy
  • analogy: totally unrelated structures–>do direct relationship in evolutionary history
  • homologous at basic structural level but analogous as independently derived structures
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14
Q

Flight in vertebrates

A
  • all use forelimb
  • Pterodactyl: super long pinky with wing suspended from it
  • bird: start with dinosaur ancestry; whole hand is fused to be sturdy support for feathers
  • bat: umbrella method; suspended on all fingers
  • HOMOLOGOUS as FORELIMBS; ANALOGOUS as WINGS
  • insect wings are ANALOGOUS IN ALL WAYS to WINGS in VERTEBRATES
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15
Q

Gene Homology

A
  • organisms have homologous genes (the same gene which represents common descent of an ancestral gene in two lineages)
  • e.g. Myoglobin-oxygen-binding protein found in tissues of all vertebrates so there are myoglobin genes
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16
Q

How can we tell if a gene is homologous to a gene from another organism?

A
  • homology criteria apply to gene sequences
  • similarity=structural criterion
  • differences in gene sequences represent the differences in the evolution of this gene in each of the species
  • correct alignment of sequences is crucial
  • positional criterion: overall molecular topology (built of similar domains)
  • local sequence base positions-different base occupies homologous position although a mutation has occurred
  • *look at example sequences
  • share lots of same genes with other vertebrates and even share some with other phyla
17
Q

General Points about homology

A
  • in evolution, pre-existing structures are often converted/co-opted to new uses
  • history matters
  • homologous structures don’t necessarily have the same function
  • evolution is branching in pattern, not linear, so homologs diverge
18
Q

Gene Homology II

A
  • certainty increases with length of DNA sequenced e.g. an entire stretch of DNA as in genomic sequencing. Often seen in gene families
  • long sequence lets us see homologous genes and the suite of mutational differences accumulated over evolution
  • useful tools in tracing evolution of both genes and organismal lineages