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

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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?

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 

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.

  • 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.

  • 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.

  • 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.

  • The result of determination is the presence of tissue-specific proteins characteristic of a cell’s structure and function 

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 

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….

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.

  • 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.

  • 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 

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.

  • 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.

  • 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) 

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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