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

GENE EXPRESSION

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 GENE ACTIVATION binds to repressor; repressor falls off the operator (fig ) 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.

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