1. Gene Expression Supplementary reading: Chapter 19 in Campbell 7 th edition

2. Background Genes serves as a recipe for building a protein molecule (these are called “structural genes”) When a particular protein is needed by the cell, the corresponding gene, made of DNA, is turned "on," or transcribed into messenger RNA, which then carries the "protein recipe" to the protein- making machinery of the cell (ribosomes) where it is translated into a protein product.

3. Overview Concept of "genes" -vs- "junk" sequences. See Chromosome 11 Flyover animation. (introns, exons, pseudogenes, transposons, etc)Chromosome 11 Flyover animation Not all genes are active in all cells Not all genes in a given cell are activated all the time There MUST be some way to control when a gene is turned "on" or "off" The activation of a gene results in transcription (mRNA made) which in turn results in the formation of a protein Chromosomes are really made up of structural genes and their ON and OFF switches ("regulatory genes") – "ON" = transcription and protein formation, "OFF" = not transcribed, no protein made

4. Prokaryotes (ex: bacteria) Much less DNA (than eukaryotes, like humans) so much easier to study The lac operon model (Jacob, Monod, Lwoff) 1965 Nobel Prizelac operon model The OPERON consists of: – Regulator gene- codes for the repressor protein – Promotor gene- attachment site for RNA polymerase enzyme, to begin transcription – Operator gene- attachment for repressor – Z, Y, a,= structural genes- code for polypeptides (in this case, for enzyme)

5. When the RNA polymerase enzyme is not blocked by the repressor (genes are "ON") it will move along the structural genes causing them to be transcribed into mRNA; this results in the enzyme being made ("expressed"). When the repressor molecule is on the operator, transcription is "blocked", so no enzyme is made. In this case, presence of lactose "induces" transcription by essentially removing the repressor from the operator.

6. ‘inducible” vs “repressible” genes Try these tutorials, for further explanation: - The Tryptophan Repressor - Combination of Switches - the Lac Operon The Tryptophan Repressor Combination of Switches - the Lac Operon operon animated explanation lac operon movie (avi) 3:24 lac operon movie

7. Eukaryotic Gene Expression Chromosome structure: chromatin (DNA helices) are wrapped around a central histone protein core. "nucleosomes": DNA wrapped around histones (proteins); forms beadlike loops in the chromatin.

8. "euchromatin": uncoiled DNA that is being transcribed "heterochromatin": tightly coiled DNA; contains inactive genes picture comparison

9. Introns and Exons Introns: “inert” noncoding sections of eukaryotic genes that are transcribed but not translated. Exons: codons for protein synthesis Pre-RNA (initial transcript) contains useful information (from exons) - coding for protein- interspersed with some “extra“ noncoding (intron) sequences. It must be modified before the ribosome can make the protein it calls for. mRNA Cleavage : “spliceosomes” cut and splice only the necessary info together, before it reaches the ribosome for translation. Watch this “Modification of mRNA : prokaryotes -vs- eukaryotes” http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter15/animations.html# short movie of mRNA editing (introns/exons)” http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter15/animations.html# short movie

10. Control of Transcription in Eukaryotes Regulatory proteins, called “transcription factors” help place the RNA polymerase at the correct spot on the promotor. “Enhancer” sequences (often located elsewhere on chromosome) are “looped in” to initiate gene expression by bringing activators on contact with the polymerase.

11. Chapter 21 in Campbell 7 th ed. “The Genetic Basis of Development” Morphogenesis (from the Greek morphê shape and genesis creation, literally, "beginning of the shape") is the biological process that causes an organism to develop its shape. It is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation.

12. Embryology Cleavage (mitotic division) Morula Blastula Blastopore Gastrulation Differentiation Deuterostomes or Protostomes

13. Differentiation into Germ Layers

14. Phylogeny: based on embryological development

15. Gene Expression during Development Unsurprisingly, special “master genes” have been found to control cell specialization (roles) as well as the placement/location of certain bodily structures, like appendages

16. Morphogenesis Homeotic Genes are regulatory genes that determine where certain anatomical structures, such as appendages, will develop in an organism during morphogenesis. Specific DNA sequences found within a homeotic gene are referred to as “homeoboxes” (Hox) These "master genes" are conserved from flies to mice to humans (determine location of body parts in human embryos as well). Can even be found in fungi and plants (control flower development)

17. When mutations occur in Hox sequences… Very well-studied in fruit flies (located on the 3rd chromosome) "Antennapedia" is a hox gene first discovered in Drosophila which controls the placement of legs. Scientists can induce mutation in this, causing legs to grow in the place where antennae are normally found (left photo) Also can manipulate the pbx (post-bithorax) and bx (bithorax) genes to this effect (right photo)

18. Specific examples of genes active in embryological development The Hedgehog (Hh) family of proteins transmits information to embryonic cells required for proper development. Different parts of the embryo have different concentrations of hedgehog signaling proteins. – The use of a single protein for such a wide variety of functions is possible because cellular responses to Hh depend on the type of responding cell, the dose of Hh received, and the time cells are exposed to Hh. The pathway also has roles in the adult. Diseases associated with the malfunction of this pathway include basal cell carcinoma.

19. There are several homologues of these genes throughout the animal kingdoms Ex: in vertebrates Desert Hedgehog (Dhh), Indian Hedgehog (Ihh), and Sonic Hedgehog (Shh) Weird example of SHH gone wrong: Janus cats. See “Frank and Louie”, who recently died @ age 15http://www.telegram.com/article/20141204/NEWS/312049633http://www.telegram.com/article/20141204/NEWS/312049633 Named for the Roman god Janus, who was usually portrayed as having two faces, domestic cats with two faces are extremely rare Janus cats are thought to have too much of the sonic hedgehog (SHH) protein, which plays a role in forming an animal's face during development. In some experiments, chick embryos exposed to an excess of SHH were born with two beaks and eyes spaced far apart.