BIO SCI 94 Lecture Notes - Lecture 12: Molecular Clock, Choanoflagellate, Linear Function

• School: UC-Irvine
• Department: Biological Sciences
• Course: BIO SCI 94
• Professor: Nancy Burley

Document Summary

Common ancestor: colonial protists similar to choanoflagellates. 635 million years ago: sponges in sedimentary rock. 750 million years ago: tiny sponge fossils. Molecular clock estimates less than 1 billion years ago. Molecular clock: tool used to calculate when lineages diverged. Based on dna substitution changes over time. Typically indicates lineages older than fossil evidence. Reliable when multiple molecular clocks give similar dates. Simultaneous appearance of numerous animal taxa and rapid diversification. Increase in oxygen from cyanobacteria and eukaryotic algae. As animals got bigger from more levels of oxygen, more niches were developed. Two consequences of antagonistic evolution: increase in body size and skeletonization (ex. teeth) In animals, hox genes specify axis and segment identity within embryo to develop certain structure. Interacting factors of the cambrian explosion positive feedback. Heterochrony: another way which animal body plans evolve. Evolutionary change in timing or rate of development.