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Bio 162 Module 3
| Question | Answer |
|---|---|
| What is ontogeny? | The development of an organism from earliest stage to maturity; all changes that happen in an organism's life |
| What is a central feature of multicellularity in metazoans and embryophytes? | Ontogenetic changes that begin with a distinct embryonic stage and continue throughout life |
| What is the group called that because of the fundamental similarity of eukaryotes, this variety of organisms can be used to study common processes such as development? | Model organisms |
| What are some model organisms? | Drosophila, C. elegans, sea urchins, mus musculus, zebra fish (Danio), and Arabidopsis (cress) |
| Where does development start? | From a single totipotent cell |
| What is a totipotent cell? Give an example. | A cell that has the ability to give rise to the entire organism (for example, a fertilized egg) |
| What are embryos? | Cells in the diploid stage of sexual reproduction and that grow by mitosis (cells are gentically identical, but genes are actively transcribed) |
| T or F: Embroyos evolved independently in Metazoans and Embryophyta. | True |
| What is the difference between embryos of metazoans and embryos of embryophyta? | Metazoan's embroyos may be protected in egg or mother, but others exist free in the environment, whereas Embryophyta have a sporophyte embryo that is always protected (there is no gametophyte embryo) |
| What are some major processes in embryonic development? (5) | - Polarity - Cleavage - Differential gene expression - Cellular Differentiation - Morphogenesis |
| What is the process of polarity in embryonic development? | Establishes axes of symmetry |
| What is the process of cleavage in embryonic development? | Growth via cell division (hyperplasia) |
| What is the process of differential gene expression in embryonic development? | Activation of different sub-sets of genes (gene networks) in different cells that leads to cell specialization |
| What is the process of cellular differentiation in embryonic development? | Generation of cell fates and phenotypes |
| What is the process of morphogeneis in embryonic development? | Formation of structures with specialized cell types |
| T or F: the processes in embryonic development all happen at different times. | False, some of these processes happen at the same time |
| When is the embryo stage complete? | When most or all organ systems are formed (more so in Metazoa) |
| What are the plant embryonic stages? (7) | 1) zygote --> 2) two cells --> 3) 8-celled embryo --> 4) globular embryo --> 5) heart embryo --> 6) torpedo embryo --> 7) mature plant |
| What is a seed in plants? | embryo (sporophyte) with energy storage and building materials |
| What is a key process during plant embryonic development that occurs during the 2-cell stage? | Establishing polarity (embryo asymmetry) |
| Do plant embryos have large scale cell migration? | No, they do not have large scale cell mitigation |
| How do embryophyte embryos begin? | With a diploid cell and then they grow by mitosis and differentiate into the sporophyte |
| What does plant embryo development prioritize? | High surface area (including cotyledons--first leaves) |
| T or F: Embryo development in many species of plants looks very similar. | True |
| What is a sporophyte? | The 2n (diploid) multicellular life stage in embryophytes |
| What are the animal embryonic stages? (6) | 1) zygote --> 2) eight cells --> 3) blastula --> 4) gastrula --> 5) larva --> 6) mature animal |
| T or F: the key process of establishing polarity (embryo asymmetry) in animals occurs at the eight cell stage. | False, establishing polarity can occur at different times in different animals |
| What does animal embryo development prioritize? | Compact organization with early determination of body axes (back vs. belly; head vs. tail; left vs. right; interior (gut) vs. middle vs. exterior (skin)) |
| Do animal embryos have large scale cell migration? | Yes, they have massive scale migration and repositioning to achieve the final body plan |
| What is a larva? | Post embryonic stage of development |
| T or F: Embryo development in many species of animals looks very similar. | False, it can look very different in different species due to the different morphologies...HOWEVER, the goals are very similar, in which they establish polarity, determine the body axes, and reposition the cells through cell migration |
| What does the early establishment of polarity lead to? | Signaling events that provide positional information relative to their neighbors and determines the body axes |
| Can polarity be established in the egg before fertilization? | Yes, in some organisms |
| What process results in initial cell divisions in the embryo, and the formation of the blastula? | Cleavage |
| What process results in the creation of discernable structures with special shapes, borders, and made of specific tissues? | Morphogenesis |
| What are the 3 processes that occur during morphogenesis? | 1) Formation of the germ layers 2) Gastrulation 3) Organogenesis |
| How does morphogenesis form the germ layers? | By using differential gene expression and cell communication |
| What are the 3 germ layers? | Ectoderm (outer), mesoderm (middle), and endoderm (inner) |
| What are somatic cells? | Give rise to the three "germ layers" (the bulk of the embryo) |
| What are germ cells? | Give rise to gametes in the new individual and are set-aside very early in development |
| What is gastrulation? | Radical cell movements that reposition cells in the three germ layers to generate a multi-layered organism |
| T or F: while the distinction between the germ layers becomes evident during gastrulation, cells are specified as one of the germ layer types much earlier, via complex signaling mechanisms | True |
| By the end of gastrulation, how are the 3 germ layers repositioned? | The ectoderm is surrounding the outside of the embryo, the endoderm is most interior (and will form the gut), the mesoderm is sandwiched between the two |
| What begins after the end of gastrulation? | Organogenesis --> the formation of organs |
| How does organogenesis begin? | With formation of the neural tube (spinal chord and brain) through neurulation, as well as the protective vertebrae in vertebrates, through somitogenesis |
| What signals the thickening of the neural plate? | The mesodermal notochord |
| What comes together to form the neural tube? | Ectodermal neural folds |
| What does the neural tube give rise to? | The central nervous system (brain and spinal chord) |
| What are neural crest cells? | Ectoderm cells from the neural fold that give rise to many different cell types, including the peripheral nerves |
| What are somites? | They are derived from rods of mesoderm on either side of the neural tube--initially forming as blocks |
| What do upper somites give rise to? | The lower part of the skin (dermis) |
| What is dermis? | The lower part of skin |
| What do middle somites give rise to? | skeletal muscles |
| What do lower somites give rise to? | Mesodermal cells that become vertebrae and ribs |
| What do all processes of embryonic development rely on? (3) | Differential gene expression, cell communication, and patterning |
| What is differential gene expression? | Allows different groups of cells to make different types of proteins, despite the fact that cells are all genetically identical (for the most part) |
| What is cell communication? | Occurs as a consequence of differential gene expression but also directs further differental gene expression |
| What is patterning? | Differential expression of homeotic genes establishes specialized body regions and location of structures |
| What are transcription factors? | They regulate the expression of other genes by activating gene networks in specific cells |
| When can differential gene expression occur? | When only a subset of the genes in the genome are transcribed |
| What does differential gene expression often involve? | 1) Often involves external signals that trigger an intracellular pathway 2) Often involves specific transcription factors moving into the nucleus to direct transcription of specific genes |
| What are often intitiated by the presence or absence of specific transcription factors within particular groups of cells? | Gene networks |
| T or F: transcription factors just activate transcription of individual target genes. | False, transcription factors either activate or repress (inhibit) transcription of individual target genes |
| What are the consequences of differential gene expression? (3) | 1) Polarity/Axis Determination 2) Germ layer specification (metazoan only) 3) Cell fate and determination |
| What is the differential gene expression consequence of polarity/axis determination? | Each cell can be given molecular coordinates about where it is and determine the body axes (anterior/posterior; dorsal/ventral, etc.) |
| What is the differential gene expression consequence of germ layer specification (in metazoans)? | After polarity is established, differential gene expression is used to establish the germ layers |
| What is the differential gene expression consequence of cell fate and determination? | Determination is a process whereby a cell and its descendants are set down a particular developmental pathway (cell determination is when cells achieve different identities) |
| What is the difference between cell determination and cell differentiation? | Cell determination is the process that sets a cell's overall fate, whereas differentiation is the process of becoming a specialized cell |
| What are 2 ways in which cell fate determination could occur? | 1) Cyctoplasmic segregation 2) Cell-cell communication |
| What is cytoplasmic segregation? | An uneven distribution of cytoplasmic materials during cleavage |
| What are the maternal effects (related to the structure of the egg) of cytoplasmic segregation? (2) | -Egg polarity--> regional localization of materials, especially maternally derived mRNAs, enzymes and transcription factors -Cleavage planes in the zygote can result in the uneven segregation of these materials between the daughter cells |
| What are stem cells? | Undifferentiated cells that are self-renewing |
| What is cell potency? | The ability to produce different lines of cells |
| What are the 4 types of cell potencies? | Totipotent, pluripotent, multipotent, and unipotent |
| What is totipotent? | Can differentiate into any cell type (the zygote and cells in early embryos) |
| What is pluripotent? | Can form most other cell types (cells in early embryos) |
| What is multipotent? | Can give rise to a limited number of cell types |
| What is unipotent? | Can produce only one type of cell |
| What is induction? | Secretion of chemical signals (inducers) by one group of cells to a nearby target (responder) cells. The inducer triggers a cascade of changes in the responder cells, often including further differential gene expression |
| What is an inducer? | The chemical signal that binds to target (responder) cells in the induction process |
| What is a responder? | Cells that bind to the inducers and are thus changed confomationally, triggering a cascade of events |
| What determines how an inductive signal will be interpreted by the responder cell? (2) | - Concentration of the inducer signal --> graded target cell response depends on how much inducer signal reaches them - Target cells must be competent to respond --> the number and type of inducer receptors |
| What is a morphogen? | A type of inducer whose concentration gradient determines a developmental pattern in embryonic plants and animals. They can provide positional information based both on differences in concentration and thresholds determined by the target cell (competency) |
| What do meristem cell in plants give rise to? | - New cells that cause growth due to increased cell number - New cells that differentiate into plant tissue, systems, and organs |
| What do apical (primary) meristems on the tips of shoots and roots of the plants give rise to? | Primary growth (lengthening the shoot and root) and tissue (dermal, ground, and vascular) and organ formation (leaves, flowers, etc.) |
| What do lateral (secondary) meristems that surround the primary stem give rise to? | Increased girth of the plant (secondary growth) and producing stem and root wood and park adding tissue |
| Wat about repair is possible in animals but not plants? | Repair is often possible in animals because stem cells can migrate to a damaged area, which is not possible in plants |
| How do plants repair when wounded or perform asexual reproduction? | Cells de-differentiate to become new meristems and then re-differentiate to produce needed structures |
| What are homeotic genes? | Master control genes that initiate a cascade of gene expression and affect the timing and amount of synthesis of proteins encoded by large number of genes |
| What could malfunctioning homeotic genes cause? | Very large-scale structural abnormalities |
| What are the 2 types of homeotic genes? | Homeobox genes and MADS-box genes |
| What are homeobox genes? | They posses similar DNA sequences of about 180 base pairs and encode proteins that facilitate transcription of other transcription factors |
| T or F: Different homeobox genes have the same sequence on either side of the homeobox | False, different homeobox genes have different sequences on either side of the homeobox |
| What are hox genes? | A group of homeobox genes that specifically direct anterior-posterior patterning in animals |
| What are 2 important aspects of hox genes? | 1) Colinearity--> order of hox genes on a chromosome is the same as the position in the body when (and where) they will be activated 2) Highly conserved--> Hox proteins in distantly related species can substitute for each other |
| What is a haltere? | A balance organ in flies that replaces a possible second wing |
| What is a Ubx protien? | A Hox protein that inhibits activation of the wing cascade resulting in a mutant fly with a extra set of wings` |
| What are the repeating structures in pants called and what to they consist of? | Phytomers that consist of nodes and internodes |
| What is a whorl in plants? | Occurs when there is a radial pattern of leaves or stems at a node |
| T of F: Buds are areas where apcial meristem cells are dividing and differentiatinf into phytomers. | True |
| How many whorls does a flower consist of? | 4 |
| What are the 4 whorls of flowers (starting at the lowest whorl)? | 1) sepals 2) petals 3) stamens 4) carpels |
| What are MADS-box genes? | They posses similar DNA sequences of about 168-180 base pairs and encode proteins that facilitate transcription of other transcription factors |
| What are organ identity genes (OIGs)? | A group of MADS-box genes that specifically direct flower whorl organ formation |
| How many types of organ identity genes are there and what controls their expression? | There are 3 types of OIGs (A, B, C) and their expression is controlled by transcription factors |
| What OIGs does each whorl express? | -Sepals --> Only A (AA) -Petals --> A and B (AB) -Stamens --> B and C (BC) -Carpels --> Only C (CC) |
| What is Evolutionary Developmental (Evo-Devo) Biology? | Understanding how changes in developmental mechanisms can create alterations in body plans over evolutionary time |
| T or F: Eukaryotic evolution involves building different structures to create novel body plans during embryo development from the same materials and using the same genes and similar regulators. | True |
| T or F: Subtle differences in regulation patterns give rise to unique structures (like pectoral fins, forelimbs, arms, wings, etc.) | True |
| What are homologous strucutres? | Structures that share the same evolutionary and developmental history (ex. bones of vertebrae wins) |
| What are analogous strucutres? | Structures that look similar and/or perform similar functions, but have different evolutionary and developmental histories (ex. the wings themselves) |
| T or F: Regulatory genes that control the expression of other "structural" and "process" genes operate together in the same regions and tissues. | False, regulatory genes that control the expression of other "structural" and "process" genes operate independently in different regions and tissues |
| How do different body plans arise? (4) | From which genes are used and the relative timing, location, and quantity of expression |
| Inherited changes to gene expression results in... | Evolution |
| T or F: Environment can play a key role in acitivating certain genes under given conditions (phenotypic plasticity). | True |
| What is heterometry? | "Different measure"--> differences in the level of gene expression |
| What is heterochrony? | "Different time"--> differences in the timing of expression (requires only very small regulatory changes and no significantly new genes) |
| What is heterotopy? | "Different space" --> Differences in the location of gene expression |
| What is heterotypy? | "Different type" --> Difference in the genes that are activated, not just their timing, or places, or amounts, which results in major morphological differences |
| What is phenotypic plasticity? | The ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions |
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ndimarco31
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