lec 18- Evo Devo

Question 1

what specific flowering plant was Darwin the most intrigued by?

Answer 1

Ophrys- the “bee orchid” genus, many species in eurasia

Question 2

what was Darwins organ for extreme perfection?

Answer 2

the eye

Question 3

when did eyes first appear?

Answer 3

during the Cambrian explosion, an adaptation for predators to see prey and vice versa

Question 4

did the eye evolve multiple times over the years?

Answer 4

yes

Question 5

what did the eyes in the Cambrian look like?

Answer 5

they had compound eyes, similar to insects

Question 6

what are the four types of eyes?

Answer 6

eye spots (flatworms), cupped eyes (scallops), compound eyes (insects), and camera eyes (cephalopods and vertebrates)

Question 7

what do all eyes share?

Answer 7

opsins to capture photons and crystalline (lens) to concentrate photons

Question 8

do sponges, some of the earliest animals, have eyes?

Answer 8

no, and they don’t have opsins

Question 9

do placozoans, the simplest animal, have eyes?

Answer 9

no, but they do have opsins but role is unknown

Question 10

what are placozoans?

Answer 10

small flat marine blobs with upper and lower complex cell layers, cilia, but no tissues or eyes, but have opsins

Question 11

where did opsins come from?

Answer 11

evolved from gene duplications of G proteins (guanine nucleotide binding proteins that act as molecular switches)

Question 12

what is the oldest opsins?

Answer 12

placopsin, found only in living placozoa, and estimated to have evolved in the Ediacaran and only signalled the presence of absence of light

Question 13

what are the four types of opsins?

Answer 13

placopsin, C opsins (red), R opsins (green), RGR-Go opsins (blue)

Question 14

which type of opsins is the most widespread?

Answer 14

R-opsin (green)

Question 15

how did crystallin evolve?

Answer 15

-heat shock proteins are expressed in muscles and other tissues that prevent proteins from clumping
-a mutation also caused it to be expressed in the early vertebrate eyes which now helps focus light and prevent clumping

Question 16

what is the flaw of the human eye?

Answer 16

-the retina is backwards by having the opsins at the back while the nerve and blood cells are in the front
-this causes a blind spot where the optic nerve is, but the brain fills it up

Question 17

how is the octopus eye better than the human eye?

Answer 17

-the retina has the opsins in the front and the nerve and blood cells in the back
-no blind spot

Question 18

what is the estimated time it takes for an eye to go from an eye spot to a functional eye with lens?

Answer 18

400,000 years

Question 19

eyes are the result of a long history of gradual evolution but each stage must be functional in what?

Answer 19

light reception

Question 20

what is important for the evolution of the eye?

Answer 20

gene duplication and recruitment

Question 21

is the eye structure constrained by history?

Answer 21

yes, because they had to modify ancestral eyes as they cannot start from scratch

Question 22

what regulatory gene initiates eye formation?

Answer 22

PAX6 gene

Question 23

is PAX6 gene highly conserved across bilaterian species?

Answer 23

yes, because PAX6 protein from a mouse can trigger eye formation in Drosophila

Question 24

what do mutations in PAX6 cause?

Answer 24

total eye loss

Question 25

what is Aniridia?

Answer 25

lack of an iris in the eye, pupil looks black and partial to total vision loss and mostly caused by mutations in PAX6

Question 26

are reduction or loss common during evolution?

Answer 26

yes, as some can be beneficial

Question 27

can a subtle change in gene expression alter a phenotype in one way?

Answer 27

no, the subtle changes of gene expression alter phenotypes in multiple ways (like beak shapes)

Question 28

can the change in timing (genetic switches) and locations of expression of developmental genes alter the shape or properties of a phenotype?

Answer 28

yes