Evolution and development

Biological diversity - evolution+development

• phylogenetic trees - express relationships between organisms

• different body plans+but common traits - share common ancester
• greater - evolutionary distance between organisms - greater, underlying differences - body plan 

• Cambrian explosion - biggest radiation - all phyla present today+others no longer seen

• Cambrian explosion  - 1st appearance, multicellular animals - radically different body architecture

• evolutionary radiations still occurring - microevolution 
• radiations involve changes - morphology+branching - new species 

• extinction - dinosaurs (end of Cretaceous) opened up - ecological niches

• human arm, feline leg, whale flipper+bat's wing = homologous structures, all derive forelimb - common ancestor
• bones underline structures = same - modified, natural selection - increase/reduction - relative size

• analogous structures don't share common ancestry 
• eg wings - birds, pterosaurs+bats. all developed - Tetrapod forelimb - different evolutionary history = convergent evolution 
• convergent evolution - hard - properly classify organisms - new methods - DNA sequencing circumvent problem

• organisms change over evolutionary time scales - change body plan
• changes = due - modifications - previously existing structures

• change - shape/size/position - pre-existing structures
• loss - pre-existing structure
• duplication - pre-existing structure
• mammalian middle ear bones derived - reptile jaw
• snakes lost cervical vertebrae+multiplied thoracic vertebrae

• all metazoans originate - single fertilised egg cell (zygote)
• zygote - several rounds division - blastocyst
• folding - layer endoderm cells causes formation - 3 cell layered gastrula
• - chordate, notocord forms+lays down axis - development of neutral tube

• details - gastrulation+neurulation differ across different phyla - bilateran animals. however all develop bilateral symmetry
• bilateria = bilaterally symmetric along 1 axis - show differentiation - 2 axes (dorso - ventral+anterior - posterior)
• show differentiation along dorso-ventral+anterior-posterior axes - embryonic development progresses

• signals between cells = clues tell cells how - differentiate, rate to grow, which direction to grow+what proteins make

• all cells - developing animal = complete complement - genes - behave differently - other cells - cell genes turned on+off = gene regulation 

• DNA = polymerised nucleotides = adenine, cytosine, guanine, thymine
• DNA sequence encodes genes - order nucleotides = arranged

• genes = blueprint - make proteins 
• genes arranged linearly - chromosome (most DNA…