Genes and Development Chapter 16

Development All the changes that occur during an organism’s lifetime Cell specialization: Cell determination: specific patterns of gene activity Cell differentiation: final step of cell specialization

Morphogenesis The development of the body plan Requires two steps: 1. Cell differentiation 2. Spatial organization These depend on:  Pattern formation, cell signaling, cell shapes, cell migrations  Regulatory genes that turn other genes on and off at appropriate times

Zygote The fertilized egg that develops into all the specialized cells needed within a multicellular organism Each specialized type of cell makes a unique set of proteins This is true despite the fact that these cells show nuclear equivalence – in other words they have the same genes

Cloning A new individual that is genetically identical  In plants: have been able to make a clone from somatic (body) cells of an adult plant  In animals: have produced clones by transferring the nucleus of a cell into an enucleated egg cell 1996: Dolly – cloned sheep in Scotland  Other mammals have been cloned since  Problems: only 1% - 2% success rate; high incidence of genetic defects

Dolly the Sheep

Rainbow and CC

Human cloning 1. Reproductive cloning – goal is making a new individual… very controversial and ‘banned’ 2. Therapeutic cloning – goal is NOT making a new person but producing stem cells

Stem Cells Undifferentiated cells that can divide to produce differentiated cells and retain the ability to reproduce themselves 1. Totipotent: potential to give rise to all body tissues 2. Pluripotent: more specialized; can give rise to many but not all types of cells

Stem cells… Potential uses:  Cures for degenerative diseases such as Parkinson’s Potential sources:  Unused human embryos from fertility clinics and newborn’s umbilical cord blood

Control of cellular DNA expression 1. Differential gene expression (Ch. 13) 2. Genomic rearrangements: physical changes in the structure of the gene eg: immune system cells do this in order to produce new antibodies in response to infection 3. Gene amplification: the copies of a particular gene are increased so that the amount of transcription of that gene can be increased

Genetic control of development: Very similar controls exist in a wide variety of organisms:  The basic mechanism evolved early and has been maintained although modified Maternal effect genes:  Organize the structure of the egg cell  Help establish the polarity of the embryo: dorsal/ventral and anterior/posterior Homeotic genes:  Specify the developmental plan for each body part

Genetic control of development… Induction: cell differentiation is influenced by interactions with neighboring cells Chronogenes: involved in developmental timing  Apoptosis – programmed cell death Eg: skin between human fingers

Cancer and Cell Development All forms of cancer have one thing in common: no divisional regulation of cells Tumor: a localized group of cells with uncontrolled cell division  Metastasis – cancer cells ‘escape’ and spread to other parts of the body  Tumors that can metastasize are malignant

Cancer and Cell Development… Genes that control cell division:  Proto-oncogenes – normal genes that control cell division Mutations can change these into oncogenes – cancer genes Some viruses carry oncogenes  Tumor suppressor genes – also put the ‘brakes’ on cell division Mutations can turn off these genes and therefore stop the suppression of a tumor