Gene Expression & Mutations SB2. Students will analyze how biological traits are passed on to successive generations. (d) Describe the relationships between changes in DNA and potential appearance of new traits including: - Alterations during replication (Insertions, Deletions, Substitutions) Mutagenic factors that can alter DNA (High energy radiation and Chemical)

Protein Synthesis REVIEW Genes are small segments of DNA that code for proteins The process of protein synthesis consists of two steps: Transcription An mRNA molecule is transcribed from a DNA template. This happens in the nucleus. Translation The coordination of tRNA and mRNA create a strand of amino acids known as a polypeptide chain. This happens on a ribosome.

Control of Gene Expression In prokaryotes, proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes Differentiation yields a variety of cell types, each expressing a different combination of genes In multicellular eukaryotes, cells become specialized as a zygote develops into a mature organism Different types of cells make different kinds of proteins Different combinations of genes are active in each type Most differentiated cells retain a complete set of genes In general, all somatic cells of a multicellular organism have the same genes

Control of Gene Expression

Amoeba Sisters: Mutations

Genetic Changes What is a mutation? A mistake or change in the genetic (DNA) make-up of an organism There are four different types of mutations Point mutations Frameshift mutations Chromosomal mutations Spontaneous mutations Mutation Story QUESTIONS TO PONDER WHILE WATCHING “MUTATION STORY” How can a mutation be harmful in one environment and helpful in another? Why should a mutation persist if it kills people? Why are there more people with sickle cell disease in one part of the world than in other parts?

Mutation Story

Point & Frameshift Mutations Point mutation Change in a single base pair in DNA THEDOGBITTHECAT Change the ending “T” to a “R” THEDOGBITTHECAR Frameshift mutation A shift in one place (deletions/insertions) HAVEANICEDAY Delete the “N” and shift everything down HAVEAICEDAY

Nonsense vs. Missense Mutations The new codon causes the protein to prematurely terminate, producing a product that is shortened and often does not function. MISSENSE The new codon causes an incorrect amino acid to be inserted into the protein. The effects on the function of the protein depend on what is inserted in place of the normal amino acid.

Chromosomal Mutation Chromosomes are physically changed Trisomy May break and rejoin incorrectly May not separate correctly (or at all) during Meiosis  NONDISJUNCTION Trisomy Example of a chromosomal mutation in which a zygote ends up with an extra chromosome

Chromosomal Mutation

Spontaneous Mutations Occur randomly Some environmental agents causes Prolonged exposure to X-rays Prolonged/excessive exposure to UV radiation Radiation exposure Certain chemicals

Inheritance of Mutations Somatic cell mutations are NOT passed on to the next generation Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.