Lecture 11 Origins of Multicellularity a Multicellularity evolved numerous times 1 Intro 2 Evolutionary origins a The fossil record i Marine fungi evolve first ii Cambrian explosion rapid increase of multicellularity iii Paleozoic brings vascular plants terrestrial arthropods terrestrial fungi iv End of Jurassic flowering plants evolve b Molecular phylogenies and genomes looking at how multicellularity evolved by examining closest unicellular relatives i Land plants closest unicellular green algae 1 Glaucophytes unicellular eukaryotes with primary plastids a Chloroplast has thin peptidoglycan wall like cyanobacteria b Could be a hint at what the ancestor looked like 2 Maybe it started simply a Chlamydomonas algal protest endosymbiotically entered volvox which has 2 cell types 3 Multicellular green plants also arose in the ocean a Multicellularity started in the ocean with sea lettuce 4 2 candidates for closest relative to land plants coleochaete or chara vulgaris a Using a molecular phylogeny you can see that charales is closer to modern land plants and is the closest unicellular relative LAND PLANTS CAME FROM OCEAN CLOSEST RELATIVE CHARALES 5 1 Choanocyte cells in sponges resemble choanoflagellate protists 2 Animal genes hidden in the choanoflagellate genome a 78 protein domains previously only found in animals found in choanoflagellate genome i Reflects the properties of the ancestor not the actual ancestor themselves 3 QUESTION why choanoflagellates benefit from coloniality a Colonies induced by chemicals from bacterial food stay in one place when good amounts of food are present reversible switch signaled by the food they eat ii Animals closest is choanoflagellates iii Fungi unicellular opisthokonts 1 Opisthokonts had 2 choices when coming to land chose to live in dirt and eat dead stuff bc that s what they did before 2 Multicellularity of fungi began in water with chytrids and diversified when on land iv Brown algae unicellular stramenophiles 1 Brown algae far away from other areas but still developed multicellularity c How did multicellularity get started i Observations of genome complexity vs organismal complexity 1 Eukaryotes genomes bigger than prokaryotes 2 Multicellular eukaryote genome bigger than protists 3 Development of multicellularity requires big complex genes ii WHICH CAME FIRST complex genome or complex organism iii Selfish DNA is bad right Maybe not 1 As population size goes down gene complexity goes up 2 As genome size goes up expressed gene number plateaus lots of junk DNA 3 Abrupt point in increasing genome size where lots of junk DNA exists 4 As pop goes down junk DNA goes up 5 Genetic drift is more of a factor in small populations as a result 6 Selfish DNA proliferate as long as they don t inactivate important genes 1 Repetitive DNA stimulates unequal crossing over 2 3 Big intergenic spaces allow more complex regulatory circuits multiple Introns allow alternative splicing and evolution of chimaeric genes 4 BIG IDEA long periods of time junk DNA eventually allowed for ways to go about creating a gene features of animals and plants a Analogy crazy hoarder then something breaks can go into their stores and get the part you need ends up being very useful 5 Junk came first before function came from selfish DNA
View Full Document
Unlocking...