evolution II Flashcards
what is the endosymbiosis theory?
βendosymbiotic theory deals with the origins of mitochondria and chloroplasts
βMitochondria and chloroplasts are believed to have developed from symbiotic bacteria.
what is some evidence for the endosymbiotic evolution of eukaryotic cells?
βmitochondria have their own circular genome which replicates independently of nuclear DNA
β new mitochondria are produced by fission of existing mitochondria
β all mitochondrial genomes share similarity with the Typhus bacterium βRickettsia prowazekiiβ
what are plastids and where are they found?
βthe plastid is a major double-membrane organelle found in the cells of plants, algae, and some other eukaryotic organisms.
what are plastid genomes and what do they encode?
βplastids possess their own genome, the plastome, and a specific machinery to decode its genetic information.
βplastid genomes encode proteins necessary for plastid function.
what are the four basic processes of multicellularity?
βspatial organisation
βchange in form
βgrowth
βdifferentiation
describe why the evolution of the eye is thought of as being convergent
βThe diversity of eyes suggests that they have evolved several times independently (polyphyletic, convergent evolution).
βthey also have features in common.
what are the common features in eukaryotic eyes?
βALL eukaryotes use a homologous family of proteins, opsins, to detect light.
βOpsins are G-protein coupled receptors that convert light to nerve impulses.
βEukaryotic opsins share sequence homology and have diverged to detect different wavelengths of light.
what are homologues, paralogues and orthologues?
βHomologues are related by descent from a common ancestor.
βParalogues are homologues within the same species.
β Orthologues are homologues between species.
how many Hox genes do vertebrates have and how have they arisen?
βVertebrates have four Hox gene clusters
βwhich have arisen from two duplication events of an ancestral chromosome.
what does Pax 6 have to do with the development of the eye?
βBeing eyeless is orthologous to Pax6 in humans and mice.
βThe ectopic (differently placed) expression of the eyeless gene in drosophilia (fruit flies) leads to ectopic eyes.
βPax6 is involved in eye development throughout the animal kingdom.
how can eye loss occur as a result of evolution? and give an example
βsome animals have evolved from surface-dwelling forms to underground forms
βEye loss is a common feature in such animals because eyes are energetically expensive
β Mexican, blind cavefish
βIts surface-dwelling ancestor has eyes, but the derived, cave-dwelling form doesnβt.
why are there differences in morphology between animals which are genetically related?
βmorphological differences are established during development.
βeven though itβs reproductive, selective pressure acts on the adult form.
βanimals share the vast majority of their genes, but the regulation of gene expression differs between them.
how do we know where Homo-sapiens come from?
βWe can get evidence from the fossil record and from molecular analyses.
βMitochondria are maternally inherited.
βThe mitochondrial genome replicates independently of the nuclear genome and does not undergo recombination
βthe male Y chromosome does not have a homologous female chromosome to recombine with.
βChanges in sequence of mtDNA and the Y chromosome are due to random mutations over time.
βanalysis of mtDNA and Y chromosome sequence shows maternal and paternal origin, respectively.
what is the RNA world hypothesis?
β early life is thought to have been based on self-replicating and self catalyzing RNA molecules
β catalytic RNAs are present in organisms from bacteria to humans
why did RNA world evolve into DNA?
βDNA is more stable than RNA
β there is a greater range of protein enzymes and they are more robust
