Evolution and Development Flashcards
What does it mean if certain animals are all mammals/share common traits?
they share a common ancestor
What do all mammals have in common?
All mammal have this in common – feed their young with milk
What does the word mammal derive from?
The word mammal derives from mammalia which mammals feed their young with.
What does it mean if an animal has a radically different body plan?
The animal is not so closely related as others
the greater the evolutionary distance between organisms…
…the greater the underlying differences in body plan
Define phyla.
the large groupings of different animals.
Define phyla chordate.
phyla of humans
What is the phyla of humans called?
phyla chordate
What is the phyla of starfish?
phyla echinoderm.
What are all phyla part of?
The bilatera
What is radial symmetry?
where any imaginary slice through the animal produces mirror images
What is an example of an animal with radial symmetry?
Cnidaria
What is bilateral symmetry?
when a left and right side and a mirror image is produced only by one cut down the centre of the animal
What are the two types of symmetry?
Bilateral symmetry and radial symmetry
What are animals with bilateral symmetry grouped as?
bilateria
What are animals with radial symmetry grouped as?
Radiata
What has happened between the phylogeny of different animals?
There is a split in the phylogeny of animals
Define the group radiata?
radially symmetrical organisms.
Define the group bilateria.
bilaterally symmetrical
What group of symmetry do Deuterostomia and Protostomia belong to?
Deuterostomia and Protostomia are both Bilateria
What group of symmetry do humans belong to?
Humans are Deuterostomia (bilateria).
Describe the symmetry of bilateria.
Bilateria are bilaterally symmetric along one axis but show differentiation on two axes (dorso-ventral and anterior-posterior)
What happens in step 1 of early embryonic development?
The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage.
What happens in step 2 of early embryonic development?
Only one cleavage stage–the eight-cell embryo–is shown here.
What happens in step 3 of early embryonic development?
In most animals, cleavage results in theformation of a multicellular stage called a blastula. The blastula of many animals is a hollow ball of cells.
What happens in step 4 of early embryonic development?
Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer).
What happens in step 5 of early embryonic development?
The blind pouch formed by gastru-lation, called the archenteron, opens to the outside via the blastopore.
What happens in step 6 of early embryonic development?
The endoderm of the archenteron develops into the tissue lining the animal’s digestive tract.
What begins to occur in step 4.
Step 4 = beginning of tissue differentiation
What is a zygote?
a fertilized egg cell.
What do all metazoans originate from?
all metazoans originate from a single fertilized egg cell (a zygote)
How multicellular organisms grow?
1) the zygote goes through several rounds of division forming a blastocyst2) folding of a layer of endoderm cells causes the formation of a three cell-layered gastrula3) in chordates a notocord forms and lays down the axis for development of the neural tube
Describe the process of embryonic development.
1) Cleavage produces the morula2) Gastrulation by invagination produces the three germ layers.3) Neurulation produces the neural tube called the neurula.
what happens in the process of gastrulation?
Tissue layers are formed.
Describe the process of gastrulation (the formation of tissue layers).
1) Some blastoderm cells invaginate to form the archenteron 2) Other blastoderm cells ingress, becoming primary mesenchyme3) Cells along the sides of the archenteron elongate.4) The mouth will form where the archenteron meets the ectoderm.5) The blastopore will form the anus of the mature animal6) Mesenchyme cells will form the mesoderm.
What does the ectoderm form?
the ectoderm forms the skin and nervous tissue
What does endoderm form?
the endoderm forms the gut, liver and lungs
What does the mesoderm form?
the mesoderm forms the musculoskeletal system and the cardiovascular system
What is the name deuterostome derived from?
the name deuterostome is derived from ‘mouth second’ – this means that in deuterostomes (including vertebrates) the mouth forms after the anus
In short, what is gastrulation?
Invagination of the cells forming a blastopore. This is the process of gastrulation
When does the mouth and anus form in deuterostomes?
In deuterostomes, the mouth forms second, the anus forms first. The word deuterostomes means mouth second.
When does the mouth and anus form in protostomes?
In protostomes, the mouth forms first. The word proteosome means mouth first.
What does the word proteostome mean?
means mouth first.
What happens after the development of the three germ layers?
cells structure then begins to form.
What does the formation of cells structure include?
this includes differentiation of the mesoderm to form the body cavity or coelom which contains the gut (derived from endoderm)
What is the development of cells controlled by?
has to be controlled by genes and proteins to ensure that correct development occurs and that body plan is laid down in such a way that the organism is functional
Why is it important that the development of cells is controlled by genes?
Ensures that the body plan is laid down in such a way that the organism is functional
What is modification related to?
where we get modification it is related to different development.
What is different development caused by?
different development is of course down to genes and proteins. those genes and proteins are subject to change via mutation
How do genes and proteins (and therefore development) changed?
those genes and proteins are subject to change via mutation
How does natural selection act on genes and proteins and therefore different development?
natural selection merely acts on random mutation to favour changes that are ‘fitter’. Causes genes to change by mutation. Causes different development.
What happens as we go back further into evolutionary history?
go back further in evolutionary history and animals show radically different body plan.i.e. deuterostome/protostome
What is all development driven by?
but all development is driven by gene expression and the action of proteins
What is the old idea from the 19th century that has gained new currency?
it was argued in the 19th Century that arthropods were simply inverted chordates and vice versa.now genes have been identified that pattern the dorso-ventral axis and the dorsal specific gene in arthropods is interchangeable with the ventral specific gene of chordates
What occurred after the cambrian explosion?
After the cambrain explosion, there was “a period of experimentation” with radically different body plans
What did the cambrian explosion see the first appearance of?
saw the first appearance of multicellular animals with radically different body architecture
What is weird about the body plans after the cambrian explosion?
Many of the body plans dont fit into the phyla we have today.
Why is the period after the cambrian explosion termed “a period of experimentation”?
organisms had radically different body plans
What question does the “period of experimentation” raise”?
does this reflect the time when body plan was laid down – so everything that evolves after this is merely the result of ‘tinkering’ with the same basic body plan?
When did the biggest radiation we know of occur?
during the Cambrian period
What happened at the time of the biggest radiation?
at this point all of the phyla that we see today are present – plus many others we no longer see
What caused phyla to change into what we see today + the extinction of other phyla during this period of biggest radiation?
increase in oxygen in the atmosphere
Why do evolutionary radiations occur?
evolutionary radiations occur because there are vacant ecological niches to fill and the environment changes.
When did the mass extinction event happen?
66 million years ago
What happened at the mass extinction event?
the extinction of the dinosaurs (asteroid - Yucatán Peninsula)
What happened at the end of the cretaceous?
the end of the Cretaceous opened up large numbers of ecological niches.
What are examples of ecological niches which opened up at the end of the cretaceous?
- niche for large grazing herbivores- niche for large carnivores- niche for large marine predators
What were the ecological niches filled by?
these were filled by mammals and in some cases birds
What is similar to ecological niches?
in a similar way colonisation of previously uninhabited environments leads to the same result – e.g. volcanic islands (Darwin’s finches – 18 species), newly formed lakes (Lake Victoria cichlids – at one point 350 species – dying out now)
Define ecological niche.
position of a species within an ecosystem.
What do mass extinctions cause?
Mass extinction events cause ecological niches.
What have organisms undergone throughout evolutionary history?
organisms have undergone dramatic radiations evolving from a limited number of forms to a great diversity of forms.
Whats an example of dramatic radiations causing evolving forms?
the radiation of mammals shortly after the demise of dinosaurs 66 million years agoprior to the end of the Cretaceous almost mammals were small insectivores
Whats an alphadon?
a Cretaceous mammal small, nocturnal (before extinction of dinosaurs)
Give an example of a niche which opens up?
marine dinosaurs – extinction – niche opens – evolution of e.g. whales.
How do we get modification?
modification can be derived by several means:1) change of shape/size/position of pre-existing structure2) loss of pre-existing structure3) duplication of pre-existing structure
What are mammalian middle ear bones derived from?
the mammalian middle ear bones are derived from the reptile jaw
How have snakes become different from lizards over time?
snakes have lost cervical vertebrae and multiplied thoracic vertebrae
Why have snakes changed from lizards?
To adapt to their environment and what it demands from them.
How do bacteria signal to other cells?
quorum sensing.
What do single celled organisms have the ability to do?
even single-celled organisms have the ability to signal to other cells
How might the gastrula have been formed originally?
perhaps single-celled animals grouped together as colonial animals then more organisation occurred and that the gastrula is a remnant of this?
Why are multicellular organisms at an advantage?
Multicellularity = bigger size – access to more things
What is quorum sensing in bacteria?
process of cell–cell communication that allows bacteria to share information about cell density and adjust gene expression accordingly
What cant we infer from development?
we cannot infer evolutionary relationships from development (ontogeny does not recapitulate phylogeny)
Where do developing bilateran animals show differentiation?
along dorso-ventral and anterior-posterior axes as embryonic development progresses
How do differentiated axes form in an organism?
these are due to positional effects – once a decision has been made as to which part of the developing cell mass is front/back or up/down cells grow according to a developmental program
How do cells know how to differentiate and grow?
signals between cells act as cues to ‘tell’ cells how to differentiate, what rate to grow at, which direction to grow, which proteins to make etc(e.g. Beta cells are sensitive to blood sugar levels - secrete insulin)
Describe how cells signal to each other to cause development and growth and differentiation?
1) Cell a produces signals2) Signals binds to receptor on cell B 3) The receptor is a protein4) Proteins secreted by cell A are perceived by cell B causing a response5) Causes changes in structure and function6) Causes growth, differentiation, and movement
What does the set of genes turned on determine?
the set of genes turned on determines cell fate
What does the activity of the cell depend on?
the activity of the cell depends upon the genes that are turned on in that cell
Why do genes have to be turned on and off?
All cells in a developing animal have a complete complement of genes – so in order to behave differently from other cells a cell must have some genes turned on and some genes turned off
What do all cells have?
a complete complement of genes
What must a cell do with its genes in order to behave differently to other cells?
in order to behave differently from other cells a cell must have some genes turned on and some genes turned off.
Define gene regulation.
Cells having some genes turned on, and some genes turned off.
What is a gene?
a sequence of nucleotides
What is a promoter?
a dna sequence which proteins called transcription factors bind to in order to turn the gene off or on.
Do all cells have transcription factors?
All cells have particular transcription factors which turn genes on or off, transcribed or not transcribed. For example, producing mRNA to be turned into protein.
What is a promoter also known as?
upstream regulatory elements.
Describe how genes are regulated to control transcription?
1) genes have upstream regulatory elements called promoters2) proteins called transcription factors bind to the promoter and control transcription by RNA polymerase3) when the transcription factor is bound to the promoter RNA polymerase transcribes the gene and the protein is made (gene on) if it is not bound RNA polymerase does not transcribe the gene (gene off)
What does the development of multicellular organisms depend on?
development of multicellular organisms (plants as well as animals) depends upon cues from other cells directing cellular differentiation – the pattern is laid down early on and depends on positional effects
What happens when a gene is transcribed?
protein made.
What can promoters also do?
mutate
What could promoter mutations cause?
This could cause an amino acid change.
What happens if the amino acid sequence changes?
If amino acid sequence changes, then the function of the protein may change.
what do proteins do?
proteins are the molecules that do the biochemical work of our cells, act as structural components but also act as signals to enact cellular differentiation
Can dna sequence mutate?
DNA sequence can mutate.ACTCCTGGATAGGCTAACTGTTACCCACTCCTGGATAG[C]CTAACTGTTACCCg (guanine) becomes a c (cytosine)
WHat may happen if a mutation occurs in the part of a chromosome that is a gene?
the amino acids that the gene encodes in the protein will be changed
Where are genes found?
In chromosomes.
What do genes code for?
An amino acid
What do amino acids make up?
A protein
What happens if a chromosome mutates?
Gene may mutate. The amino acid it codes for therefore changes. The protein the amino acids make up changes.
WHat mutations effect development?
- DNA mutations- promoter mutations
Where were homeobox genes discovered?
discovered in the fruit fly, Drosophila.
Describe the functions of homeobox genes.
1) they encode transcription factors that turn other regulatory genes off or on2) Homeobox genes are like the transcription factor for the transcription factors, and can turn them on or off (suppressing their activity).
When are homeobox genes turned on?
Homeobox genes are turned on at certain points during development.
In what order are homeobox genes arranged?
Arranged on the chromosome in the order they are expressed in the embryo.
Do humans have just one or multiple homeobox genes?
Humans have multiple homeobox genes.
What are homeobox genes refferred to as?
“master switches”
What are homeobox genes responsible for?
each responsible for development of a different domain
What is the role of homeobox genes in development?
regulating the development and patterning of multicellular organisms. They are involved in the formation of body plans, the development of organs, and the specification of cell types.
What do homeobox genes regulate?
homeotic genes are genes which regulate the development of anatomical structures
What does overexpression of the homeobox gene ‘antennapedia’ cause?
overexpression of the homeobox gene called antennapedia causes legs to grow on the head instead of antennae – this transcription factor normally controls development of legs on the thoracic segments
What happens when the homeobox gene ‘ultrabithorax (ubx)’ is overexpressed?
the homeobox gene, ultrabithorax (Ubx) is usually expressed in the third thoracic segment – it represses genes involved in making wings and so halteres develop instead.
What happens when homeobox gene ubx is knocked out?
knocking out Ubx causes a second set of wings to grow in place of halteres.
What does the homeobox encode and what is the homebox part of?
the homeobox is a part of a gene that encodes the homeodomain which forms part of the protein which binds to DNA regulatory elemenst upstream of other transcription factors that then turn on or off gene expressionit is a master control switch
What is eyeless?
eyeless is a gene in Drosophila encoding a transcription factor that controls the development of eyes – Drosophila mutants without this gene have no eyes
What happens to Drosophila mutants if they do not have the eyeless gene?
they have no eyes.
What happens when the eyeless gene is overexpressed in drosophila?
where it is expressed functional eyes form in unusual places for instance here on legs.
What happens if the mouse version of the eyeless gene is inserted into Drosophila?
the most remarkable thing of all is that the mouse version of this gene can be inserted into Drosophila and revert eyeless mutants back to wildtype (homologous gene).
Why does the mouse version of eyeless work on Drosophila?
even though the mammalian eye and the insect eye are vastly different the patterning for their formation on the head is conserved between mammals and insects.
What is the role of homeobox genes in development of mammalian limbs?
Homeobox genes also control distal development of the mammalian limb
What is required from homeobox genes for correct development?
sequential expression is required for correct development
What do mutations in homeobox genes which are responsible for mammalian limb development cause?
mutations in these particular homeobox genes lead to conditions such as synpolydactyly
Describe finger bones in bats wing.
Extended finger bones in bat wings, which are adapted to function.
Where was the hedgehog gene first identified?
The hedgehog gene (hh) was first identified in the fruit flyDrosophila melanogaster
What happens if the hedgehog gene is expressed in mutant phenotype embryos?
mutant phenotype embryos to be covered with small pointy projections.
Whats the sonic headgehog?
A secreted protein.
Who was the morphogen sonic hedgehog model first proposed by?
Lewis Wolpert (the French Flag Model).
What did Lewis Wolpert propose determined cell fate?
cell fate determined by gradients of morphogens
What are morphogens?
substances thioguht to be involved in the patterning of cells during embryonic development.
What does the precise concentration of morphogen determine?
determine which transcription factors are turned on which then determines what kind of cell results.
What is development of cells in neural tubes affected by?
the development of the cells in the neural tube are affected by concentrations of sonic hedgehog protein
Do homeotic mutations only occur in animals?
homeotic mutations also occur in plants
Why do plants have homeotic mutations if they dont have homeobox genes?
although plants do not have homeobox genes they also have homeotic mutations arising from master control genes – MADS box genes – transcription factors
Do plants have homeobox genes?
No.
What is Arabidopsis?
They are small flowering plants related to cabbage and mustard.
What is floral organ identity of Arabidopsis defined by?
floral organ identity is defined by expression of different transcription factors in different zones
What happens if a gene of Arabidopsis is removed?
removal of one of the genes changes the identity of the organ produced in that zone
What is development of body plan dependant on and why?
as the development of body plan is under control of genes, it is dependent on DNA sequence.
What changes in developmental genes can drive modification?
- mutations causing changes in the homeobox protein itself may affect development2. mutations to the promoters that the transcription factors bind to may affect development
What might the mutation of development genes change?
these changes may alter the time that other genes are turned on, the region that is affected - may grow larger or become smaller – different genes may be upregulated or downregulated
What genes does natural selection choose?
Natural selection choses those genes that produce individuals best suited to their environment.
