Evo-devo

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• heterochrony evolutionary change in developmental timing compared to ancestor or other species
• sequence heterochrony Focuses on changes in the order of developmental events, rather than just the timing of the entire process
• allometric heterochrony a type of evolutionary change in developmental timing that results in differences in the scaling relationships between body parts and overall size
• paedomorphosis “Child-form”. Development is slowed down or ends early, resulting in adult organisms retaining juvenile features of ancestors
• peramorphosis beyond-form”. Development is extended or accelerated, resulting in exaggerated or more developed traits in descendants
• neoteny Slower physical development resulting in a sexually mature juvenile form
• progenesis Early cessation of development. Halting of development before full physical maturity.
• postdisplacement A delay in the start of development.
• acceleration Increased rate of development. Ex, teeth in some mammals develop earlier.
• hypermorphosis Extended duration of development. Structure has more time to develop.
• predisplacement Early onset of a developmental process.
• genetic fixation Happens when only one allele of a particular gene remains within a population. This means all individuals will carry two copies of that same allele. Reduces genetic variety within the population and all individuals become genetically identical with respect to this particular allele
• allele Variant of a gene
• phenotype Observable characteristic or trait of an organism
• co-option Existing structures are repurposed for new functions. Ex, feathers first evolved for insulation but would later aid in flight.
• denaturation DNA is heated to about 95°C which causes the two strands to separate like a zipper
• annealing The mixture is cooled to about 50-60°C so that primers (short pieces of DNA) can bind to the specific DNA sequence.
• extension The temperature is raised to ca 72°C and an enzyme called DNA polymerase adds new DNA bases, copying the target DNA.
• phage promoter Specific DNA sequence that acts as a binding site for RNA polymerase, initiating the transcription of a phage gene.
• germ disc a dense, circular patch of cells that assembles on one side of the yolky egg after fertilization
• germ band a thickened strip of cells that marks the embryo’s main body axis.
• histology Science of studying tissue under a microscope
• chondrocytes The sole cell type in cartilage. Are responsible for growth within the epiphyseal growth plates which leads to bone lengthening
• ostracoderm Informal group of vertebrate animals that include jawless armored fish.
• paraformaldehyde is used for preservation and to prevent degradation
• PBST removes residual fixative and maintains isotonic conditions. Also prepares the tissue for staining.
• ethanol dehydrates the tissue which improves dye penetration
• MgCl2 is used to enhance the dye binding and is used less in younger embryos with less mineralization.
• hydrogen peroxide oxidizes pigmentation
• potassium hydroxide softens the tissue and allows better visualization

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