snake venom is an example of

a complex adaptation

complex adaptations are

phenotypic traits requiring multiple, specific mutations to yield a functional advantage

coexpressed traits that experience selection for a

common, often novel, function

DNA can code for

gene, proteins, and RNA molecules

gene control regions

an upstream section of DNA that includes the promoter region as well as other regulatory sequences that influence the transcription of DNA

a promoter is a

region of DNA upstream of a gene where revelant proteins (such as the RNA polymerase and transcription factors) bind to initiate transcription of that gene

gene control regions can also

bind repressors or transcription factors to regulate the expression of nearby genes

a repressor

is a protein that binds to a sequence of DNA or RNA and inhibits the expression of one of more genes

a transcription factor

is a protein that binds to specific DNA sequences and acts like a light switch by turning all the sequences on or off simultaneously

regulatory networks are often

involved in complex adaptations

regulatory network is a

system of interacting genes, transcription factors, promoters, RNA, an other molecules. It functions like a biological circuit, responding to signals with output that controls the activation of genes, during development, the cell cycle, and the activation of metabolic pathways.

hox genes

a set of transcription factor genes show unusual property, provide a glimpse of one way where gene expression is translated into the many different forms that metazoans (animals) exhibit.

hox genes, in contrast, are genes that

specify segment identify and they are all clustered together in one (usually) tidy spot. Within that cluster, there is even further evidence of order. The genome seems to have various randomly scattered genes, with no order present in the arrangement on a chromosome, the order is only shown in expression thru the process of development.

drosophila has

8 hox genes in a row, and the genes' order within that row shows their order of expression in the fly body. (3' end of DNA strand [denoted lab: labial] is shown in the head, right of the DNA strand [abd-B: abdominal-B] is shown at the end of the fly's abdomen)

hierarchical gene organization controls

development of animal embryos

some expressed genes shut down other genes, for example Distallelss (DII), involved

in the production of antennae and legs, is repressed by homothorax (hth) and so is not expressed in the abdomen of the fly

hox genes are expressed

during development (development genes)

knocking out individual Hox genes in Drosophila causes

homeotic transformations (one body part develops into another)

Antennapedia mutant

lega develop on the fly's head instead of antennae

Hox genes enable the

development of morphologically distinct regions in a segmented animal (activation from the 3' end s the start of a segment to develop into part of the head)

mutations to genes at the top of the hierarchy can have

drastic effects

gene duplication can produce

novel functions

promiscuous proteins

capable of carrying out two functions; likely to take on new functions if duplicated

paralog

homologous gene that arises by gene duplication

gene recruitment

co-option of a particular gene or network for a totally different function as a result of a mutation; reorganization of a preexisting regulatory network can be a major evolutionary event

New adaptations in microbes: E.coli long term evolution experiment

12 initially identical populations of asexual Escherichia coli bacteria, evolved the ability to feed on citrate in the growing medium in the absence of oxygen

snake venoms evolved through

duplication and co-option

crotamine genes in snake venome are

closely related to beta-defensins the bacteria-fighting molecules found in many vertebrates

regulatory mutation led to

production of defensin gene in the mouth

venom genes have been recruited from

genes expressed in many organs in snakes

venom evolved before

snaked evolved

directional terminology

anterior: front

posterior: rear

dorsal: back

ventral: belly

proximal: close to center of mass

distal: away from the center of mass

hox genes are part of a conserved

"genetic toolkit" among animals (common ancestor passed this gene to flies and mammoths[diverse animals])

dorsal-ventral patterning is conserved; flies and mice use

homologous genes for dorsal-ventral patterning, though they are expressed as "mirror images"

the phylogeny of animals informs as to how

the genetic toolkit was deployed (dorsal-ventral patterning and single nerve cord in annelids, anthropods, and vertebrates)

mouse legs start as a bulge known as a limb bud

mice build proximal structures then more distal structures

fly legs develop as a series of concentric structures

the "bulls-eye" is the most distal part of the leg

ortholog

is one of two or more homologous genes separated by a speciation event

paralogs

homologous genes produced by gene duplication, that are both possessed by the same species

fly and mouse leg genes reflect

derivation from genes in a common ancestor

in flies, Engrailed (En) gene helps

define the posterior portion of the limb bud in mice. its ortholog in mice has an identical role in the leg disk

in flies, engrailed proteins

turn on the expression of the signaling gene Hedgehog (Hh)

combination of signals (high Hh and absence of En) causes

cells to begin expressing two additional signaling genes Decaptenaplegic (Dpp) and Wingless (Wg), these interact to produce (DII) and (EGFR) affecting the development of limb

blocking Shh gene expression

stops limb patterning pathway

fins appear in the

foosil record 400 mys

in fish mesodermal tissues produce

a cluster of skeletal bones near the base of the fin

AER (apical ectodermal ridge) (Hoxa11 and Hoxd13 overlap)

stimulated distal growth of the limb bones in the mesodermal tissue (when Hox genes ceases, fin rays begin to grow from extodermal ridge tissue)

in tetrapods, skeletal bones derived from

the mesoderm become much longer, forming the long bones of the limb (later the smaller bones develop)

in tetrapod limbs, Hox genes become

active a second time later in development and their domains of expression no longer overlap (evolution of tetrapods limbs involves changes to the timing and location)

Hoxd13 in development of a fish fin (create an appendage with a striking resemblance to a tetrapod limb)

this is a pleiotropic effect, simultaneously shrinking the outer area of the fin where fin rays develop and expanding the region where bone grows

expression differences in a single gene give

rise to limb elongation

increased expression of Bmp2 stimulates

extra growth in the finger bones of bat forelimbs

complex eyes have evolved in

several different lineages

each kind eye contains ___ for directing incoming light and ___ opsins for capturing it. But particular molecule for each eye are different.

crystallins, opsins

crystallin

water-soluble structural protein found in the lens and the cornea of the eye for transparency

opsins

proteins that bind to light-reactive chemicals to underline vision, phototaxis, circadian rhythms, and other light meditates responses of organisms

opsins evolved in a

common ancestor around 1 bya

crystallins evolved though

gene recruitment

gene recruitment (or co-option)

the placement of a new gene under a foreign regulatory system, can lead to increase in genomic complexity, is recognized as major driving force in evolution

laws of physics

atmospheric O2 concentrations constrain insect size

antagonistic pleitropy

single gene affects expression of many traits mutations may have positive effects for one trait but negative effects for another trait

antagonistic pleiotropy: number of cervical vertebrae in all mammals

7 in their necks

note the routing of the recurrent laryngeal nerve in the giraffe neck,

carries the constraint of looping around gill arch blood vessels

convergent evolution

independent evolution leading to similar traits in two different lineages (similar selection pressures)

parallel evolution

independent evolution of similar traits in multiple lineages, all starting from a similar ancestral condition

cavefish species exhibit

parallel evolution in depigmentation

deep homology

growth and development of traits in different lineages result from underlying mechanism inherited from a common ancestor

deep homology may help to

explain cases of parallel evolution