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ZOOLOGY 300 > Week 4 > Flashcards

Week 4 Flashcards

1
Q

Long branch attraction

A
  • A systematic error where terminals with long branches are erroneously placed together
  • Parsimony approaches are highly prone to LBA and suffer from statistical inconsistency
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2
Q

Statistical inconsistency

A

As more data accumulates, support increases for the wrong answer

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3
Q

Intuitive example of LBA

A

Nematoda and Tardigrada

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4
Q

Gastrulation

A

Cells in one region of the blastula begin to involute, forming a cavity called the archenteron

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5
Q

archenteron

A

cavity in blastula during gastrulation

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6
Q

Mesoderm formation

A

After gastrulation, a middle layer of cells forms from the endoderm, which is called the mesoderm
- In dipoblastic animals, the mesoderm is highly reduced or absent
- In triploblastic animals, all three tissue types are present
- Either formed from dividing cells between endoderm and ectoderm or formed from pouching of the endoderm

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7
Q

dipoblastic

A

mesoderm is highly reduced or absent

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8
Q

triploblastic

A

all three tissue types are present

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9
Q

Schizocoely

A

Mesoderm is formed from dividing cells in the space between endoderm and ectoderm

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10
Q

Enterocoely

A

Mesoderm is formed from pouching of the endoderm (archenteric pouching)

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11
Q

Ectoderm gives rise to

A

Skin, neurons

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12
Q

Mesoderm gives rise to

A

Muscle, red blood cells, bones

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13
Q

Endoderm gives rise to

A

Stomach, thyroid, lung cells

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14
Q

Nephrozoa divided into two major clades

A
  • deuterostomes
  • protostomes (more than 95% of described animal species)
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15
Q

Protostomes three major clades

A
  • Spiralia (the largest) (also called lophotrochozoa)
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16
Q

Spiralia

A
  • Uniting characteristic: spiral cleavage
  • many spiralians have a trochophore larva
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17
Q

spiral cleavage

A
  • starting with the 4-cell stage, tilting of the mitotic spindles results in cleavage planes neither perpendicular not parallel to the axis
  • Spiral cleavage is highly stereotypical and the cell lineage can be mapped during embryogenesis
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18
Q

Trochophore larva

A

Common in spiralia
Characterisitcs:
- Apical tuft of cilia (sense organ)
- Prototroch (band of locomotory cilia)
- Perianal telotroch
- Mid-entral neurotroch
- through gut (mouth, stomach, and anus)
- protonephridia
- Free swimming

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19
Q

Phylum Annelida

A
  • Triboblastic, coelomate animals
    -bilaterally symmetrical
  • segmented; segments arise by teloblastic growth
  • through gut
  • closed circulatory system
  • well developed nervous system
  • lateral, segmentally arranged epidermal chaetae
  • trochophore larva
  • marine, freshwater, terrestrial
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20
Q

Coelomate

A

Any animal possessing a fluid-filled cavity within which the digestive system is suspended.

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21
Q

Segmentation

A

-A condition where most internal and external parts are repeated along the antero-posterior axis
- serial homology
- metamerism

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22
Q

serial homology

A

The condition of repeated body parts along an axis

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23
Q

Metamerism

A

repetition of homologous structures within segments (organs)

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24
Q

annuli

A

Body segmented externally as rings

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25
Q

coelomic compartments

A

Body segmented internally separated by intersegmental septa

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26
Q

septa

A

separate internal coelomic compartments

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27
Q

Heads of annelids composed of

A
  • Prostomium (eyes, palps, tentacles/antennae)
  • Peristomium (mouth, jaws, cirri)
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28
Q

Pygidium

A

Terminal region of annelid, bears anus

29
Q

Internal segmentation

A

some organs are serially repeated in each segment
- Nephridia
- Circumferential muscles
- Nervous system ganglia

30
Q

Excretion and osmoregulation

A

-All animals need to get rid of nitrogenous waste products (ammonia, urea)
- freshwater and terrestrial organisms struggle to balance net movement of ions and water against concentration gradient

31
Q

Nephridia

A

(in many invertebrate animals) a tubule open to the exterior which acts as an organ of excretion or osmoregulation. It typically has ciliated or flagellated cells and absorptive walls.
- Protonephridium
- Metanephridium
- Antennal gland
- Malpighian tubules

32
Q

Protonephridium

A

-Proximally closed canals between the ectoderm and the endoderm; they lead outward toward the epidermis
The beating of the flagella drives fluids down nephridioduct, creating a lowered pressure in the tubules lumen
-Lowered pressure draws in surrounding fluids, carrying wastes across thin cell membranes
- Common in animals with reduced or absent body cavity (coelom) (flatworms, larva…)
- Protonephridia are rare in adult animals with true coelom

33
Q

Metanephridium

A
  • Opens outside to body wall, but also aopen internally to body fluids
  • Multicellular organ
  • large volume of liquid is taken into the ciliated, open nephrostome
    -Body fluid passed through nephridial tubule where nonwaste components are selectively absorbed back into the body through tubule walls
  • Not found in animals with no coelom or small animals
  • One one or more pairs occur in large coelomate animals (mollusks, annelids,..)
34
Q

Annelid circulatory system

A

-Closed circulatory system due to their internal compartmentalization
- Gas exchange structures (branchiae) are found as trunk filaments, anterior gills or tentacular branchial crowns on the head
- In polychaetes that lack appendages, the entire body surface functions in gas exchange; others use vascularized potions such as gills

35
Q

Homonomous segmentation

A

Condition where segments appear identical or nearly identical in shape or size

36
Q

Heteronomous segmentation

A

Condition where groups of segments are markedly different from other groups of segments

37
Q

Annelid appendages

A
  • two lobes in their primitive condition: dorsal notopodium and ventral neuropodium
  • each lob has its own bundle of chaetae
38
Q

Chaetae

A

-Chitinous bristles of annelida are bundles of largely hollow cylinders produced by an epidermal follicle
- Chaetoblast cell at base of follicle bears microvilli around which the cylinders form; the chaetae are secreted by the chaetoblast and adjacent follicle cells

39
Q

Major groups of annelids

A
  • Polychaetes
  • Oligochaetes
  • Hirundinea
40
Q

Polychaetes

A
  • Annelids with many chaetae per segment
41
Q

Oligochaetes

A
  • Annelids with few chaetae per segment and no parapodia
  • Head appendages not elaborate
  • Hermaphroditic
  • Few segments modified into clitellum, a secretory region that functions in reproduction
  • earth worm
42
Q

Hirudinea (leeches)

A

-Annelids with no chaetae or parapodia and a reduced coelomic space
-Fixed number of segments (typically 34) with external annulation
- Internal and external segmentation do not match
- Anterior and posterior suckers
-Clitellum present
-Hermaphroditic

43
Q

Diverse feeding modes of polychaetes

A
  • predators (Active and passive)
  • Deposit feeders
  • Suspension feeders
  • symbionts/parasites
  • Hosts to chemosymbionts
44
Q

Polychaete phylogeny

A

Paraphyletic

45
Q

Annelid groups that have lost segmentation

A

-Echiura
- Sipuncula
- Siboglinidae

46
Q

Sipuncula

A
  • Coelomate, non-segmented worms
  • Body divided into trunk and proboscis
  • spiral cleavage, trochophore larva
  • No chaetae
  • Two metanephridia
  • U-shaped gut (through gut, mouth and anus open in anterior half of body since these worms reside in rock)
  • Approx 150 species
47
Q

Echiura

A

-Coelomate, non-segmented worms (spoon worms)
- Body divided into trunk and probiscis
- Spiral cleavage, trochophore larva
- Chaetae present
- 1-10 pairs of metanephridia
- straight gut with posterior anus
- approx 140 species
- sex determination is environmental

48
Q

Siboglindidae

A

-Tentacles (palps) on small head region
- Trunk region with chaetae
- Multisegmented posterior region but unsegmented anterior region
- Rings of chaetae (uncini) in opisthosoma
- Midgut filled with endosymbiotic, chemosymbiotic bateria
- Mouth and parts of digestive tract are absent in adults
- Live in hydrothermal vents or sulfide-rich environments

49
Q

Where do segments come from

A
  • The larva grows through the proliferation of cells in the growth zone
  • segments are produced bu proliferation of the mesoderm anterior of the pygidium
50
Q

What phyla are segmented

A
  • Chordata
  • Arthropoda
  • Annelida
51
Q

How are segments patterend at the molecular level

A

-In Chordata, segments are called somites
- Somites are added from posterior region called the paraxial somitic mesoderm (PSM)
- Undifferentiated cells undergo fate specification and then differentiation

52
Q

Somites

A

Segments in chordata

53
Q

Paraxial somitic mesoderm (PSM)

A

Where somites are added from in chordata

54
Q

Gene regulatory network

A
  • Gene expression can be dependent on the expression of other genes and can influence the expression of other genes
  • Description of how genes regulate one another
  • The sum of the regulatory interactions make up a network
55
Q

Regular arrows

A

Indicate that one gene activates another (the one it’s pointing at)

56
Q

Perpendicular arrows

A

Indicate that one gene represses the expression of another (the one its “pointing” at)

57
Q

Morphogens

A
  • Morphogens typically have a concentration gradient that is proportional to the distance from the morphogen source
  • The higher the morphogen concentration, the more likely it is to cause a reaction or response (morphogen threshold)
58
Q

Clock and wavefront model of somitogenesis

A
  • PSM cells forming a somite undergo an abrupt change in cellular properties from one state to another
  • An oscillator controls the response of PSM cells to the mechanism triggering the transition
59
Q

First empirical evidence of oscillator

A
  • Chick embryo forms a somite every 90 minutes (oscillator)
  • Somite formation associated with a traveling wave of gene expression (wavefront)
  • Gene expression can be measured using the abundance of mRNA
  • The gene expressed in an oscillatory manner is hairy-1
60
Q

The Notch-Delta signaling pathway

A
  • Cell signaling pathway common to metazoa
  • Product of the gene Notch is a transmembrane protein with two domains (intracellular and extracellular)
  • The Notch extracellular domain of one cell can bind to the Delta domain of another cell causing the Notch intracellular domain (NICD) to be cleaved and transported to the nucleus
  • In the nucleus the NICD activates transcription of a suite of downstream genes including the hairy/enhancer of split (Hes) family of genes
  • One of the targets of NICD activation is Lunatic fringe (Lfng)
  • Lfng represses Notch, creating a negative feedback loop
  • Result: a wavefront (gene expression wave with a beginning and end)
61
Q

Segmentation associated with

A

bilaterally symmetrical stripes of gene expression

62
Q

Segmentation genes

A

Genes required for patterning segments

63
Q

Segmentation in arthropods

A

Embryos of spiders express both Notch and Delta stripes in the posterior of the embryo

64
Q

Disruption of Notch and Delta in vertebrates AND spiders

A

Results in disrupted segmentation
Conclusion: some arthropods make segments the same way as vertebrates
- Segments form from posterior of embryo
- Notch delta signaling is required
- Many genes involved in segmentation are homologous in vertebrates and arthropods

65
Q

Wnt signaling in segmentation

A
  • A key signal transduction pathway in animals
    -When Wnt gene is present, B-catenin escapes the GSK3 destruction complex and can enter the nucleus to activate genes
66
Q

Wnt and Caudal signaling in segmentation

A

-In insects, Wnt genes like Wnt 1 are necessary for the expression of caudal
- Caudal is a posterior axis marker that keeps cells in a proliferative, undifferentiated state
-Like Notch and Delta, expression of Wnt is dynamic as the segment forms
- Both genes are necessary for proper segmentation patterning

67
Q

Segmentation in annelids

A
  • engrailed and wingless are genes required for antero-posterior polarity of segments in arthropods
  • Homologs of these two genes are expressed as stripes in an annelid embryo
  • As more segments are added, more stripes of gene expression occur
  • Notch-Delta pathway members are also expressed in striped patterns which suggests an involvement of Notch signaling in segmentation for all three segmented phyla
  • Hedgehod (hh), patched (ptc), and cubitus interruptus (ci or Gli) are bona fide segmentation genes in arthropods
68
Q

Hedgehod (hh)

A
  • Hedgehog signaling is necessary for segment formation in arthropods
  • Cyclopamine is an inhibitor of hedgehog
  • In larvae trated with cyclopaminne, stripes of expression of the segmentation genes are lost (embryo fails to form segmented external and internal structures)
69
Q

Evidence for segmentation in arthropods and annelids not being identical

A
  • The position of the genes ptc and Gli are different in arthropods and annelids
  • The placement of appendages is also different

ZOOLOGY 300 (5 decks)

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