chapter 1

• Development is the set of processes by which a multicellular organism generates a complex phenotype of heterogenous cells arranged in a particular size and shape
• In animal organogenesis, three germ layers—endoderm, ectoderm, and mesoderm—are specified early in development and give rise to specific organ systems
• zygote-A fertilized egg with a diploid chromosomal complement (zygotic genome). The single-celled stage of embryogenesis
• aristotle- first known embryologist
• different animal life cycles- oviparity, viviparity, ovoviviparity
• oviparity- animals are born from eggs (birds, frogs, invertebrates)
• viviparity- live birth (placental animals)
• ovoviviparity- an egg that hatches inside the body (reptiles,sharks)
• pattern formation is seem early in the embryo
• differentiation- The process by which an unspecialized cell becomes specialized into one of the many cell types that make up the body.
• The organization of the cells of the body into functional structures via coordinated cell growth, cell migration, and cell death
• cells know when to stop dividing
• The gametes—sperm and egg—are highly specialized cells that can transmit the instructions for making an organism from one generation to the next
• environmental integrations like smoking while pregnant or doing drugs
• embryogenesis- The stages of development between fertilization and hatching (or birth).
• animals life cycle- fertilization, cleavage, gastrulation, organogenesis, 3 crucial axes developed, metamorphosis, germ and somatic cell differentiation, gametogenesis
• fertilization-fusion of the mature sex cells
• cleavage- mitotic divisions (cytoplasm) from blastomeres to blastula (sphere)
• gastrulation- extensive cell arrangements (gastrula stage) (3 germ layers: endoderm, ectoderm, mesoderm)
• endoderm- innermost layer, epithelium or digestive tube
• ectoderm- outside of embryo, epidermis, nervous system
• mesoderm- between endoderm and ectoderm (blood, heart, kidney, gonads, bones, muscles)
• organogenesis- formation of specific organs at specific sites (certain cells undergo migration from origin to final location)
• 3 crucial axes- anterior-posterior axis, dorsal-ventral axis, right-left axis
• gametogenesis- development of gametes (has to physically mature)
• Cleavage is regulated by proteins and mRNAs that have been stored in the oocyte cytoplasm
• at the end of gastrulation, the ectoderm covers the outside of the embryo, the gut-producing endoderm is deep inside the embryo, and the organ-forming mesoderm is between the endoderm and ectoderm
• Having undergone meiosis, the mature sperm and egg nuclei can unite in fertilization, restoring the diploid chromosome number and initiating the events that lead to development and the continuation of the circle of life.
• epithelial cell- tightly connected to one another in sheets or tubes
• mesenchymal cells- unconnected or loosely connected to one another and can operate as independent units
• gastrulation is the most important!
• Although patterns of gastrulation vary enormously throughout the animal kingdom, all are combinations of six basic types of cell movements: invagination, involution, ingression, delamination, epiboly, and convergent extension
• By the end of gastrulation the cells have moved into new positions and established interactions with new neighbors. The three germ layers of the organism are evident: the cells of the endoderm and mesoderm have been brought to the inside of the embryo, while the ectoderm spreads over its outside surface. The stage is set for the interactions of these newly positioned tissues.
• "find it, lose it, leave it"- find a method to get the data you need, remove the cells you were looking for to corroborate your first findings, move the cells elsewhere to further support your findings. The “find it” experiment tells you that there is an association between one thing (tissue, cell, gene) and another (organ, process, enzyme). The “lose it” experiment tells you whether the thing now lost is necessary for a given process, and the “move it” experiment tells you whether that thing is sufficient for that process
• fate map- Diagrams based on having followed cell lineages from specific regions of the embryo in order to “map” larval or adult structures onto the region of the embryo from which they arose. The superimposition of a map of “what is to be” onto a structure that has yet to develop into these organs.
• you apply vital dyes to the regions of interest
• fluorescent dyes that are so intense that once injected into individual cells, they can still be detected in the progeny of these cells many divisions later
• One way of following the fates of individual cells is to create embryos in which the same organism contains cells with different genetic constitutions
• chimeric embryo- Embryo made from tissues of more than one genetic source.
• transgene- Exogenous DNA or gene introduced through experimental manipulation into a cell’s genome.