REGULATION OF GENE EXPRESSION

1. REGULATION OF GENE EXPRESSION • Gene Interactions • The simplest form of gene interaction: Dominant vs. recessive • Incomplete Dominance • Josef Kolreuter: white/red carnations yielded pink • colors are not blended; F-2 generation had a reappearance • The active allele doesn’t compensate for the inactive allele • Codominance • Both alleles are expressed (active) • Roan cattle and erminette chickens • Written with both capital letters • Polygenic Inheritance • Traits controlled by two or more genes • Color of hair and eyes, shape and size of the nose

2. GENE EXPRESSION

3. GENE EXPRESSION IN PROKARYOTES • THE OPERON • Francois Jacob & Jacques Monod • Regions involved in the regulation and expression of nearby gene clusters. • Three Parts • a cluster of genes working together • a region of the chromosome near the cluster: operator • a region of the chromosome next to the operator: promotor • products that initiates the production of enzymes are inducers • THE REPRESSOR • Protein responsible for turning “off” the operon • See fig. 10-18 • GENE ACTIVATION • binds to repressor; repressor falls off the operator (fig. 10-19) • RNA polymerase binds to promotor, moves across to the genes, & produces mRNA. When cell runs out of the inducer, repressor binds to operator, and the operator is turned off.

4. GENE EXPRESSION IN EUKARYOTES • Inducers also active in eukaryotes • 1976 Philip Sharp and Susan Berget • mRNA produced during transcription may be altered before it is used to make proteins during translation. • Exons: “Expressed” sequences that are a complementary code for proteins. • Introns: “Intervening” sequences that are not a complementary code for proteins. • RNA moves along a gene, it transcribes the entire gene, so pre-mRNA contains introns. • Before protein can be produced, the pre-mRNA must be processes into functional mRNA • The introns are removed and the exons are spliced back together • The mRNA must complete this process before it leaves the nucleus • See fig. 10-21