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Chapter 21 Reading Quiz

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Chapter 21 Reading Quiz. When cells become specialized in structure & function, it is called … Name 2 of the 5 “model organisms”. What does it mean to be “totipotent”? What is the name for programmed cell death during development? What is a chimera?.

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chapter 21 reading quiz
Chapter 21 Reading Quiz
  • When cells become specialized in structure & function, it is called …
  • Name 2 of the 5 “model organisms”.
  • What does it mean to be “totipotent”?
  • What is the name for programmed cell death during development?
  • What is a chimera?
1 distinguish between the patterns of morphogenesis in plants and in animals
1. Distinguish between the patterns of morphogenesis in plants and in animals.
  • Morphogenesis  development for the overall shape
  • Animals  movement of cells and tissues are involved in the development of the physical form
  • Plants  not limited to embryonic and juvenile periods as it is in animals

- roots and shoot tips of plants possess apical meristems for continuous growth 

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2. List the animals used as models for developmental biology research and provide a rationale for their choice.
  • Drosophila melanogaster easily grown in lab, short generation time, embryos outside mom’s body
  • Caenorhabditis elegans  nematode; easily grown, transparent body, cell types arise in same way, hermaphroditic, short generation time
  • Danio rerio  zebrafish; small and easy to breed, transparent embryo, rapid embryonic development, small genome size
  • Mus musculus  mouse, more complex organism, yet much is known (background info) 
3 describe how genomic equivalence was determined for plants and animals
3. Describe how genomic equivalence was determined for plants and animals.
  • Genomic equivalence  nearly all of the cells of an organism have the same genes
  • Because the cells of animals will not often divide in culture, scientists have adopted alternative approaches to examine genomic equivalence: transplanting nuclei of differentiated cells into enucleated egg cells of frogs
  • Plants’ genomic equivalence was demonstrated by experiments in which entire individuals developed from differentiated somatic cells 
4 describe what kinds of changes occur to the genome during differentiation
4. Describe what kinds of changes occur to the genome during differentiation.
  • Earliest changes are subtle and at the molecular level  known as determination
  • Differences among the cells of a multicellular organism arise from different patterns of gene expression, not differences in the genomes of the cells
  • Transplantation (frog egg) showed that the nuclei do change in some ways during differentiation
  • Changes do not occur to the sequence of DNA but rather in chromatin structure 
5 describe the general processes by which dolly was cloned
5. Describe the general processes by which “Dolly” was cloned.
  • The nucleus of a dedifferentiated mammary cell from one sheep was transplanted into an unfertilized, enucleated egg of another sheep 
6 describe the molecular basis of determination
6. Describe the molecular basis of determination.
  • The result of determination is the presence of tissue-specific proteins characteristic of a cell’s structure and function 
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7. Describe the two sources of information that instruct a cell to express genes at the appropriate time.
  • Information in the cytoplasm of the unfertilized egg, in the form of RNA and protein, that is of maternal origin
  • Chemical signals produced by neighboring embryonic cells; such signals, through a process called “induction” influence the growth and differentiation of adjacent cells 
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8. Describe how Drosophila were used to explain basic aspects of pattern formation (axis formation and segmentation).
  • Pattern formation  the spatial organization of tissues and organs characteristic of a mature organism
  • Identified how specific molecules influence position and direct differentiation
  • The life cycle  fruit flies are segmented: head, thorax, abdomen

- cytoplasmic determinants provide positional information

- after fertilization, orientation of segments and development of associated structures is initiated

  • Genetic analysis of early development

- using mutants identified 1200 genes essential for development of which 120 are for segmentation

- various determinants in the cytoplasm control the expression of segmentation genes continued 

number 8 continued
Number 8 continued….

Axis formation 

  • Gradients of maternal molecules in the early embryo control axis formation (maternal effect genes)
  • One set helps to establish anterior-posterior axis of the embryo
  • Second set is involved with the dorsal-ventral axis
  • The means by which maternal effect genes influence pattern formation is exemplified by the BICOID gene (essential for the anterior end) 
9 describe how homeotic genes serve to identify parts of the developing organism
9. Describe how homeotic genes serve to identify parts of the developing organism.
  • Homeotic genes  master regulatory genes
  • Encode for transcription factors that influence the genes responsible for specific structures
  • Ex: homeotic proteins produced in cells of a particular thoracic segment lead to leg development
  • Homeotic mutations replace structures characteristic of one part of an animal with structures normally found at some other location 
10 provide evidence of the conservation of homeobox sequences
10. Provide evidence of the conservation of homeobox sequences.
  • The homeotic genes of Drosophila all contain a 180 nucleotide sequence called the homeobox
  • Sequences identical or very similar to the homeobox of Drosophila have been discovered in other invertebrates and vertebrates along with yeast and prokaryotes
  • Such sequence similarity suggests that the homeobox sequence emerged early during the evolution of life
  • Not all homeobox genes serve as homeotic genes, yet most homeobox genes are associated with some aspect of development 
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11. Describe how the study of nematodes contributed to the general understanding of embryonic induction.
  • Sequential inductions control organ formation
  • The effect of an inducer can depend on its concentration
  • Inducers operate through signal systems similar to those in adult organisms
  • Induction results in the selective activation or inactivation of specific genes within the target cell
  • Increasing concentration of inducers stimulate division and differentiation 
12 describe how apoptosis functions in normal and abnormal development
12. Describe how apoptosis functions in normal and abnormal development.
  • Apoptosis  selective, programmed cell death
  • Normal pattern formation depends on apoptosis

- occurs 131 times during normal development

- chemical signals initiate the activation of a cascade of “suicide genes”

  • Abnormal  certain degenerative diseases and cancers may have their basis in faulty apoptotic mechanisms 
13 describe how the study of tomatoes has contributed to the understanding of flower development
13. Describe how the study of tomatoes has contributed to the understanding of flower development.
  • Environmental cues (ex: day length) initiate processes that convert shoot meristems to flower meristems
  • This induction is exemplified by tomato flowers
  • Mixing mutant and wild-type plants resulted in floral meristems in which the three cell layers did not all arise from the same “parent”
  • These layers’ sources were traced and it was determined that the number of organs/flowers depended on genes in the L3 cell layer (the innermost) 
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14. Describe how the study of Arabidopsis has contributed to the understanding of organ identity in plants.
  • Organ-identity genes determine the type of structure that will grow from a meristem

- they are analogous to homeotic genes

- they are divided into 3 classes: A, B, and C

 these 3 genes direct the formation of four types of organs

  • They appear to be acting like master regulatory genes that control the transcription of other genes directly involved in plant morphogenesis

- do Not contain the homeobox sequence 

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