W4 Evolution II Flashcards
Eukaryotic cell evolution
Eukaryotic cells contain a nucleus, organelles and plastids (mitochondria/chloroplasts)
Eukaryotic cells arose through endosymbiosis or predation of protobacteria and archaeal host
Endosymbiosis generated organelles, and nucleus
Evidence for endosymbiotic evolution of eukaryotic cells
Mitochondria have their own circular genome which replicates independently of nuclear DNA
New mitochondria are produced by fission of existing mitochondria
All mitochondrial genomes share similarity with the Typhus bacterium Rickettsia prowazekii
Rickettsiales are obligate, intracellular parasites or symbionts of eukaryotes
Plastid genomes
Plastid genomes encode proteins necessary for plastid function
Loss of genes compared to ancestral form
“Lost” genes present in nuclear genome
The evolution of multicellularity
Multicellularity is usually a characteristic of eukaryotes
How did muticellularity and complex organisms evolve?
Four basic processes of multicellularity
Spatial organisation
Change in form
Growth
Differentiation
Eye evolution
The diversity of eyes suggests that they have evolved several times independently (polyphyletic, convergent evolution)
Crystallins in different taxa are not related
ALL eukaryotes use a homologous family of proteins, opsins, to detect light
Opsins are G-protein coupled receptors that convert light to nerve impulses
Eukaryotic opsins share sequence homology and have diverged to detect different wavelengths of light
(Prokaryotes also have GPCR opsins, but with a different molecular origin – convergent evolution)
Homologues, paralogues and orthologues
Homologues are related by descent from a common ancestor
Paralogues are homologues within the same species
Orthologues are homologues between species
Hox genes
Paralogs duplicated within ancestral animals
Present in clusters along chromosome
Present in vertebrates
Chromosomal organisation and function conserved
Hox gene evolution
Vertebrates have 4 Hox gene clusters, which have arisen from two duplication events of an ancestral chromosome
Gene order along the chromosome corresponds to the position of expression within the embryo
Pax 6 and eye development
Eyeless is orthologous to Pax6 in humans (aniridia) and mouse (smalleye)
Ectopic expression of eyeless in Drosophila > ectopic eyes
Mouse Pax6 gene functions in fly
Pax6 involved in eye development throughout animal kingdom
Eye loss during evolution
Some animals have evolved from surface-dwelling forms to underground forms
Eye loss is a common feature in such animals (energy costs of maintaining eyes that have no use)
Exemplified by the Mexican, blind cavefish
What makes humans human
Compare genomic sequences of humans with that of closely related species (chimps, macaque)
Identify sequences conserved in other animals, but LOST in humans – hCONDELs (human, conserved, deleted)
583 regions identified, across all chromosomes, median size 2804bp
hCONDEL
A hCONDEL near the Androgen Receptor gene (detects/responds to testosterone w/out genes no penile species, lost in humans so no penile spines)
Use the chimp or mouse sequence to drive reporter gene expression in a transgenic mouse (blue staining)
Expression seen in whiskers (vibrissae) and genital tubercle
These structures are testosterone dependent (AR-mediated)
Loss of enhancer in humans (red triangle) correlates with loss of penile spines
Mitochondrial evolution
Mitochondria are maternally inherited
The mitochondrial genome replicates independently of the nuclear genome and does not undergo recombination
Similarly, the male Y chromosome does not have a homologous female chromosome to recombine with
Changes in sequence of mtDNA and the Y chromosome are due to random mutations over time
Analysis of mtDNA and Y chromosome sequence shows maternal and paternal origin, respectively
