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2.E.1 timing and coordination

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1 2.E.1 timing and coordination
Read Chapter Watch bozeman science video “timing and coordination” Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms. Draw 6 boxes on your paper

2 The determination of different cell types (cell fates) precedes differentiation and involves the expression of genes for tissue-specific proteins. Tissue-specific proteins enable differentiated cells to carry out specific tasks.

3 Cell differentiation follows determination as the cell continues on a specific developmental path. Differentiation results in cell types such as nerve cells, blood cells, and muscle cells.

4 A single-celled zygote can develop into a multicellular adult organism that contains hundreds of different cell types.  

5 Totipotent cells are stem cells that can form all the cell types in a body, plus placental cells. Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent. 

6 Pluripotent cells can give rise to all of the cell types that make up the body; embryonic stem cells are considered pluripotent.

7 The transformation from a zygote into an organism results from three interrelated processes:
Cell division: the zygote gives rise to a large number of cells through a succession of mitotic cell divisions Cell differentiation: cells become specialized in structure and function Morphogenesis: the processes that give shape to the organism and its various parts

8 Box #1 Compare cell differentiation and cell division.

9 Genomic Equivalence: Nearly all the cells of an organism have the same genome. Cells differentiate through differential gene expression.

10 Hierarchy of Gene Activity in Early Drosophila Development
Observable cell differentiation results from the expression of genes for tissue-specific proteins. Hierarchy of Gene Activity in Early Drosophila Development Maternal effect genes (egg-polarity genes) Gap genes Pair-rule genes Segment polarity genes Homeotic genes of the embryo Other genes of the embryo Segmentation genes of the embryo


12 Box #2 Describe the function of tissue specific proteins.

13 Regulation of transcription factors during development results in sequential gene expression. Transcription factors are proteins that bind to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA.

14 Cell signaling helps direct daughter cells down the appropriate pathways, a process called induction. Cells induce neighboring cells to differentiate. 4 Anterior EMBRYO Posterior Receptor Signal protein daughter cell of 3 Will go on to form muscle and gonads form adult intestine 1 2 3

15 During induction, signal molecules from embryonic cells cause transcriptional changes in nearby target cells. Early embryo (32 cells) Signal transduction pathway NUCLEUS Signal receptor Signal molecule (inducer)

16 An inducing signal produced by one cell in the embryo can initiate a chain of inductions that results in the formation of a particular organ.

17 Homeotic genes are involved in developmental patterns and sequences.

18 Box #3 Describe how induction can lead to the development of an organism.

19 Hox genes are a group of related homeotic genes that control the body plan of the embryo.

20 Pattern formation in animals and plants results from similar genetic and cellular mechanisms. Pattern formation is the development of a spatial organization of tissues and organs. Occurs continually in plants Is mostly limited to embryos and juveniles in animals

21 An identical or very similar nucleotide sequence has been discovered in the homeotic genes of both vertebrates and invertebrates. Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse




25 Embryonic induction in development results in the correct timing of events.


27 Box # 4 Describe the function of homeotic genes

28 Temperature and the availability of water determine seed germination in most plants.

29 Genetic mutations can result in abnormal development.
Snake with one limb.

30 Box # 5 Describe environmental and mutations effect on development

31   Genetic transplantation experiments support the link between gene expression and normal development.

32 In nuclear transplantation, the nucleus of an unfertilized egg cell or zygote is replaced with the nucleus of a differentiated cell.

33 Experiments with frog embryos have shown that a transplanted nucleus can often support normal development of the egg. Frog embryo Frog egg cell Frog tadpole Less differ- entiated cell Donor nucleus trans- planted Enucleated egg cell Fully differ- entiated (intestinal) cell Most develop into tadpoles <2% develop

34 In 1997, Scottish researchers cloned a lamb from an adult sheep by nuclear transplantation.
Dolly the Sheep

35 Reproductive Cloning

36 “Copy Cat” was the first cat ever cloned.

37 In most nuclear transplantation studies, few cloned embryos develop normally.

38 Genetic regulation by microRNAs plays an important role in the development of organisms and the control of cellular functions.

39  MicroRNA (miRNA) are a small, non-coding RNA molecules that function in post-transcriptional regulation of gene expression. They generally bind to their target mRNAs and repress protein synthesis by destabilizing the mRNA. 

40 Programmed cell death (apoptosis) plays a role in the normal development and differentiation. Cell signaling is involved in programmed cell death.

41 Example: Morphogenesis of fingers and toes
Apoptosis plays a critical role in the sculpting of digits in vertebrate limbs. The death of the cells that would otherwise form inter‐digital webbing enables individual fingers and toes to be formed. Example: Morphogenesis of fingers and toes

42 Example: Development in the nematode C. elegans
As early as the four-cell stage in C. elegans, cell signaling helps direct daughter cells down the appropriate pathways. Induction is also critical later in nematode development as the embryo passes through three larval stages prior to becoming an adult. A protein in the outer mitochondrial membrane serves as a master regulator of apoptosis . Zygote Nervous system, outer skin, mus- culature Musculature, gonads Outer skin, nervous system Germ line (future gametes) Musculature First cell division Time after fertilization (hours) 10 Hatching Intestine Eggs Vulva ANTERIOR POSTERIOR 1.2 mm Example: Development in the nematode C. elegans

43 Example: Flower development
Floral meristems contain three cell types that affect flower development. Carpel Petal Stamen Sepal Floral meristem Tomato flower Cell layers L1 L2 L3 Example: Flower development

44 Box #6 How does apoptosis aid in development?

45 Learning Objectives: LO 2.31 The student can connect concepts in and across domains to show that timing and coordination of specific events are necessary for normal development in an organism and that these events are regulated by multiple mechanisms. [See SP 7.2] LO 2.32 The student is able to use a graph or diagram to analyze situations or solve problems (quantitatively or qualitatively) that involve timing and coordination of events necessary for normal development in an organism. [See SP 1.4] LO 2.33 The student is able to justify scientific claims with scientific evidence to show that timing and coordination of several events are necessary for normal development in an organism and that these events are regulated by multiple mechanisms. [See SP 6.1] LO 2.34 The student is able to describe the role of programmed cell death in development and differentiation, the reuse of molecules, and the maintenance of dynamic homeostasis. [See SP 7.1]

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