lec 18- Evo Devo Flashcards
what specific flowering plant was Darwin the most intrigued by?
Ophrys- the “bee orchid” genus, many species in eurasia
what was Darwins organ for extreme perfection?
the eye
when did eyes first appear?
during the Cambrian explosion, an adaptation for predators to see prey and vice versa
did the eye evolve multiple times over the years?
yes
what did the eyes in the Cambrian look like?
they had compound eyes, similar to insects
what are the four types of eyes?
eye spots (flatworms), cupped eyes (scallops), compound eyes (insects), and camera eyes (cephalopods and vertebrates)
what do all eyes share?
opsins to capture photons and crystalline (lens) to concentrate photons
do sponges, some of the earliest animals, have eyes?
no, and they don’t have opsins
do placozoans, the simplest animal, have eyes?
no, but they do have opsins but role is unknown
what are placozoans?
small flat marine blobs with upper and lower complex cell layers, cilia, but no tissues or eyes, but have opsins
where did opsins come from?
evolved from gene duplications of G proteins (guanine nucleotide binding proteins that act as molecular switches)
what is the oldest opsins?
placopsin, found only in living placozoa, and estimated to have evolved in the Ediacaran and only signalled the presence of absence of light
what are the four types of opsins?
placopsin, C opsins (red), R opsins (green), RGR-Go opsins (blue)
which type of opsins is the most widespread?
R-opsin (green)
how did crystallin evolve?
-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
what is the flaw of the human eye?
-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
how is the octopus eye better than the human eye?
-the retina has the opsins in the front and the nerve and blood cells in the back
-no blind spot
what is the estimated time it takes for an eye to go from an eye spot to a functional eye with lens?
400,000 years
eyes are the result of a long history of gradual evolution but each stage must be functional in what?
light reception
what is important for the evolution of the eye?
gene duplication and recruitment
is the eye structure constrained by history?
yes, because they had to modify ancestral eyes as they cannot start from scratch
what regulatory gene initiates eye formation?
PAX6 gene
is PAX6 gene highly conserved across bilaterian species?
yes, because PAX6 protein from a mouse can trigger eye formation in Drosophila
what do mutations in PAX6 cause?
total eye loss
what is Aniridia?
lack of an iris in the eye, pupil looks black and partial to total vision loss and mostly caused by mutations in PAX6
are reduction or loss common during evolution?
yes, as some can be beneficial
can a subtle change in gene expression alter a phenotype in one way?
no, the subtle changes of gene expression alter phenotypes in multiple ways (like beak shapes)
can the change in timing (genetic switches) and locations of expression of developmental genes alter the shape or properties of a phenotype?
yes
