2 From single cell to multicellular organism: A. Embryonic development =cell determination differentiation morphogenesisOne week
3 -apical meristems (stems and roots) in plants are perpetual embryonic regions,continually growing.
4 Researchers use the “model organisms” to study development:1. Mus musculus = mouse2. Drosophila melanogaster = fruit fly3. Caenorhabditis elegans = nematode4. Danio rerio = zebrafish5. Arabidopsis thaliana = common wall cressThese are model organisms because they have:1. readily observable embryos2. short generation times3. relatively small genomes4. preexisting knowledge of organism
6 The C. elegans have 959 somatic cells. Researchers have mapped out exactly howthey develop into adulthood. These aretransparent worms.This is a cell lineage; a fate map,showing what cells are destined to become.
7 Cells differentiate based on which genes are turned on and which genes are turned off.Different types of cells in an organism havethe same DNA. This is called “genomicequivalence.”Can differentiated cells ever become awhole new organism?In many plant species, you can takedifferentiated cells and create a newplant.This is called “Totipotency.”The new organism becomes a clone ofthe parent plant.
9 Nuclear Transplantation: Differentiatedcells fromanimals usuallyfail to become anew organism.The ability ofthe transplantednucleus tosupport develop-ment dependson the age ofthe donor anEmbryo tadpole developsTadpole <2% develop
10 Cloning the first mammal: Dolly, the sheep: In 1997, Ian Wilmutcloned an adult sheep by nuclear trans-plantation:
11 Mammary cells“starved” so thatcells go into G0phase.Mammary nucleiare implantedinto egg that hasbeen denucleated.Egg will grow inculture and thenwhen an embryois formed, it willbe implantedsurgically into theuterus of a sheep.
12 After 256 tries,Dolly was born.Dolly died after6 years of lifedue to a lungdisease; shealso had arthritis.However, beforeher death, shewas able to have4 offspring.
13 Stem cells: Unspecialized cells that that continually reproduce, and under specificconditions, differentiate into specialized cells.
14 Stem cells are multipotent, or pluripotent, which means they can become many typesof cells.
15 Stem cell research is of great interest because with it, we may be able to repairdamaged organs by adding healthy, newcells.a. Parkinsons: Brain cellsb. Diabetics: Pancreatic cellsanisamples/generalscience/stemcells.html
16 Determination leads up to differentiation in cells.As an organism develops, cells becomecommitted to its final state – it is“determined.”The first sign of differentiation is whenmRNA for specific proteins are made. code for that cell’s “tissue-specificproteins.”
17 “Master Control/Regulatory Genes” commit the cell.
18 How are the “master control gene” turned on? Maternal cytoplasm in the egg containsmaternal proteins, mRNA, and organelles,not equally spread out in the egg:These maternalmolecules are called“cytoplasmicdeterminants.”Unevenly distributed,they will turn oncertain genes.
19 Cells can synthesize signal molecules that turn on genes in neighboring cells.This is called induction.Pattern formation:the development ofa spatialorganization inwhich the tissuesand organs of anorganism are all intheir characteristicplaces.
20 Pattern formation in the fruit fly: “Positional Information” tells a cell where itis located relative to the body axes and toneighboring cells. They are molecules thatdetermine how the cell will respond tomolecular signals.
21 Mitosis takes placewithout cytokinesisAfter the 10th division,the nuclei migrateoutward. After the 13thdivision, plasmamembrane forms aroundeach nuclei.
22 HIERARCHY OF GENE ACTIVITY IN DROSOPHILA DEVELOPMENT(A cascade of gene activations sets up the segmentation pattern)(Basicsubdivisionsalong the A-P axis)(Segmentsin pairs)
26 B.After segment polarity genes are turned on, The homeotic genes direct the identity ofbody parts (antennae, legs, and wingsdevelop on appropriate segments).All homeotic genes of Drosophila include a180-nucleotide sequence called thehomeobox, which specifies a60-amino-acid homeodomain.An identical or very similar sequence ofnucleotides (often called Hox genes) arefound in many other animals, includinghumans.
31 Programmed Cell Death: “Apoptosis” Required for normal development. It iscontrolled by apoptosis genes, “suicide genes.”Examples:-Hands and feet-Neurons; surplus cells eliminated-Endometrium at the start of menstrual cycle
32 Regulated by changes in the activity of proteins