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Lecture 14

BIOLOGY 1M03 Lecture 14: 14- Hox gene, Evo-Devo, Gene Duplications, Dating Methods and Diversification

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Ben Evans

Bio 1M03 February 4, 2016 Hox gene, Evo-Devo, Gene Duplications, Dating Methods and Diversification Did Gene Duplication Trigger the Cambrian Explosion? - Some researchers predicted a strong association between the order in which animal lineages appeared during evolutionary history - The number of Hox genes present in each lineage and each lineage’s morphological complexity and body size - The logic behind this new genes, new bodies hypothesis was that existing homeotic genes could have been duplicated before and during the Cambrian explosion, producing new body plans and appendages - The number of genes in the Hox cluster appears to have expanded in some groups (like vertebras) during the course of evolution - But clearly this is not the only cause for morphological diversification - Insects for example are extraordinarily diverse morphologically but have less Hox genes than vertebrates - Both duplication of Hox genes and changes in expression and function of existing genes have been important in the elaboration of animal body plans - Hox genes - Late Precambrian or Phanerozoic origin - Sponge and jellyfish Hox homologs do not have temporal, spatial or quantitative co-linearity - Multiple synapomorphies - All of the bilateral organisms have co-linearity (suggests ancestor had the gene) - Ancestor originates during the Cambrian explosion - Proterostomes - Bilatera - Deuterostomes - Expansion of central Hox gene - Expansion of posterior Hox gene - Expansion in different parts of the Hox gene due to evolution - Segmental duplication - Genome duplication - How did copy number of Hox genes change? o Gene duplication o Genome duplication: duplicates all the genes o Genes can be lost due to mutation and evolution - What happens when genes duplicate? o Non-functionalization: most common, one copy of the gene does not express the gene o Redundancy: instead of having one copy, there is two o Neofunctionalization: duplication and then mutation which gives a different function to one of the duplicates o Subfunctionalization: a multifunctional protein, function is degraded rather than enhanced in a complementary way, produce a function product but must be combined in order to work How does Morphological Diversification Occur in Animals? - Changes in Hox gene number, increasing or decreasing the number of genes which affect the body plan - Broad changes of Hox expression, changes in the domain of expression - Subtle changes within Hox domains, activation or avoidance of genes - Changes in regulation of function of downstream gene, the target of expression changes How Humans Evolved - Human evolution in its entirety began with the origin of cellular life - 3.8 billion years ago - The time from our shrew-like insectivorous ancestors scurried through leaf litter in forests (100 mya until present) - If the entire evolution of the planet occurred in one day mammals would have appeared in the last 32 minutes of the day - Humans would’ve diverged in the last 2 minutes - Humans would have dispersed out of Africa in the last 2 seconds of the day - Your life would be 400 millionths of a second - The entire semester would take 6 millionths of a second Life’s Timeline - Mammals and angiosperms first appeared in the Mesozoic Era - But most extant mammals diversified in the Cenozoic Era First True Mammals - The Cenozoic Era (65 mya-present) saw spectacular radiation of mammals - Following the extinction of the dinosaurs - This was coupled in time, and probably linked to the diversification of angiosperm plants Angiosperm - Type of vascular plant that have flow
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