lec 3- origins of vertebrates

Question 1

what is the earliest chordate?

Answer 1

pikaia

Question 2

how old is pikaia?

Answer 2

540 mya

Question 3

where was pikaia found?

Answer 3

Burgess Shale

Question 4

what is the ancestor of all vertebrates?

Answer 4

pikaia

Question 5

has there ever been fossils of groups in intermediate forms?

Answer 5

no

Question 6

what were the first known chordates?

Answer 6

cathaymyrus and pikaia

Question 7

what are our closest invertebrate relatives?

Answer 7

cephalochordata and urochordata

Question 8

what is the cephalochordate fossil that was found in yunnan province in China, and is said to be 10 million years older than pikaia?

Answer 8

cathaymyrus diadexus

Question 9

what is the first potential vertebrate?

Answer 9

-haikouichthys

Question 10

are yunnanozoas vertebrates?

Answer 10

yes

Question 11

what are the two first known vertebrates?

Answer 11

-myllokunmingia and haikouichthys
-pushed the origin of vertebrates back by 40 million years
-530 Myo fossils of the first fish

Question 12

what are the characteristics of the first known fish?

Answer 12

-3 cm long
-cranium
-W-shaped myomeres
-jawless
-no bone or mineralized scales
-dorsal fin and ribbon-like pair of ventrolateral projections
-cartilaginous gill supports

Question 13

where was metaspriggina found?

Answer 13

-marble canyon, Kootenay national park
-over 100 specimen

Question 14

what are the features of metaspriggina?

Answer 14

-notochord
-w shaped myomeres
-post anal tail
-eyes with camera type lenses
-paired nasal sacs
-gills with supports plus a slightly larger anterior arch with no gill tissue

Question 15

what is an example of cephalochordata?

Answer 15

amphioxus, a 5 cm long fish like form

Question 16

what are the characteristics of amphioxus?

Answer 16

-no paired fins
-free swimming
-mostly buried in mud
-notochord
-cartilage-like material around pharyngeal region and dorsal fin
-no cranium
-major blood vessels
-no blood cells or respiratory pigments
-no heart
-has contractile vessels

Question 17

how is the digestive tract in amphioxus?

Answer 17

-buccal cavity with circle of stiffened cirri
-pharynx for food collection
-gut is a simple one way tube
-pharyngeal slits used for feeding and not respiration

Question 18

what are the two important differences between cephalochordata and vertebrata?

Answer 18

-method of excretion are flame cells in cephalochordata
-cephalochordata lack strong cephalization, few sense organs associated with head

Question 19

what are seasquirts and tunicates?

Answer 19

urochordata

Question 20

what are the characteristics of seasquirts?

Answer 20

-adults have a pharynx which is an enlarged set of internal gills
-atrial and branchial siphons
-sessile (don’t move)

Question 21

what are the characteristics of tunicates?

Answer 21

-the larva are tadpole-like
-pharyngeal slits
-muscular post anal tail
-dorsal hollow nerve cord
-notochord
-free swimming

Question 22

is urochordata a sister group to vertebrata?

Answer 22

yes

Question 23

are cephalochordata closer to echinoderms?

Answer 23

yes

Question 24

what is the hypothesis behind how the first vertebrate evolved?

Answer 24

Garstang’s hypothesis: cephalochordates and vertebrates evolved from an ancestor that resembled a larva of urochordata that became sexually mature in larval form

Question 25

did the ancestor of cephalochordates and vertebrates have sessile adults?

Answer 25

yes

Question 26

what was the body plan prior to the evolution of chordata?

Answer 26

it was inverted

Question 27

what were the characteristics of the last common ancestor of chordata?

Answer 27

-free swimming adult -elongated tail

Question 28

did metamorphosis evolve separately in cephalochordata, urochordata, and vertebrata?

Answer 28

yes

Question 29

do amphioxus and lampreys have the same gene operating in the same parts of their bodies?

Answer 29

yes

Question 30

what are Hox genes?

Answer 30

-master regulators of development -highly conserved throughout evolution -expressed in embryo and the adult -critical in anterior and posterior organization of an organism

Question 31

do all animals have Homeobox genes?

Answer 31

yes

Question 32

does increased complexity of body mean more Hox genes?

Answer 32

yes

Question 33

how are Hox genes usually arranged?

Answer 33

in clusters

Question 34

do plants and fungi have Homeobox genes?

Answer 34

yes but they aren't clustered

Question 35

what potentially caused invertebrates to turn into vertebrates?

Answer 35

-the duplication of the entire cluster of Hox genes in ancestral chordate -new germ layer neural crest may also be involved

Question 36

do agnathans have twice the number of Hox genes of cephalochordates?

Answer 36

yes

Question 37

have urochordates lost some Hox genes?

Answer 37

yes

Question 38

when did the first duplication of Hox genes occur?

Answer 38

in mid/late Cambrian (550-600 mya)

Question 39

when did second duplication of Hox genes occur? how did it occur?

Answer 39

in mid/late ordiviscian (490-510 Mya) by interspecific hybridization and is only found in jawed vertebrates

Question 40

after each duplication of Hox genes, what occurs?

Answer 40

the loss of some genes and rearrangement in some groups

Question 41

when did the third duplication of Hox genes occur? in what did it occur?

Answer 41

occured 450-460 Mya in teleosts

Question 42

in what did the fourth duplication of Hox genes occur?

Answer 42

salmonids

Question 43

what do microRNAs do?

Answer 43

regulate gene expression

Question 44

how many miRNA families in vertebrates?

Answer 44

50 +, may associated with vertebrate specific tissues like liver, pancreas etc.

Question 45

are methylation levels low in non vertebrates?

Answer 45

yes

Question 46

what does hypermethylation of promoters result in?

Answer 46

gene silencing

Question 47

is methylation higher in miRNA regions than gene encoding regions?

Answer 47

yes

Question 48

why did methylation evolve in vertebrates?

Answer 48

because a more complex way of regulating gene expression was needed when genomes became larger