GENETICS Genetics is the study of the transmission of things from one generation to the next Genetic characteristics of a population can change over time –“Evolution” These things can be –Traits / characteristics –Chromosomes –Genes

GENETIC VARIATION Genetic variation is produced in two ways – through Mutation Heritable changes in DNA sequence –Through Gene transfer Acquiring genes from another member of our species

MUTATION Inheritable change in DNA sequence Relatively rare Generally occur during DNA replication or repair –May also occur in response to mobile DNA elements Transposons and viruses May affect gene expression

SPONTANEOUS MUTATIONS Occur without effects of outside agents –Radiation, chemical mutagens, etc. Various types 1.Base substitutions One or more base pairs changed 2.Insertions and deletions Sometimes caused by transposable elements –Jumping genes Insertion of one or more bases Deletion of one or more bases

MUTATIONS POINT MUTATION One base pair altered Substitution can change the entire reading frame of the DNA causing reading frame of the DNA causing 1. Silent mutation – no result because same Amino Acid is produced (lucky there was no change) 2. Missense mutation Wrong AA produced which messes up the protein (Sickle Cell Anemia) 3. Nonsense mutation Stop command results, so proteins don’t even get made properly

Substitution

Insertion Mutations

MUTATIONS Insertions & Deletion Mutations “Frameshift mutations” Insertion or deletion of base pair(s) –e.g., GGA  GAGA (gly  glu) Generally alter reading frame –“Frameshift” –All downstream amino acids altered Protein function generally affected –Typically “knockout” mutants

Insertion / deletion & genes that jump “Transposons” = “Jumping Genes” Transposons are DNA segments spontaneously entering or exiting chromosomes Transposition into a gene constitutes a large insertion –Gene is generally inactivated Transposition out of a gene may restore gene function

TRANSPOSABLE ELEMENTS First discovered by Barbara McClintock in the 1940s Worked with maize (corn) Kernel color varied as DNA sequences jumped in and jumped out, messing with the pigment genes  no pigment  partial pigment  normal pigment

TRANSPOSABLE ELEMENTS Discovered them in 1940s, but nobody paid attention Ideas finally accepted in 1970s Nobel prize in 1983 – –She was 81 years old!! Some of Barbara’s historically significant research plots were destroyed by nutcases protesting genetic engineering – –None of the plants were engineered

INDUCED MUTATIONS Some mutations occur spontaneously –Rare Certain chemicals or radiation can cause mutations –We call these “Mutagens” –Greatly increase the frequency of mutations e.g., 1,000X or more

INDUCED MUTATIONS Chemical Mutagens ChemicalsRadiation –Ultraviolet –Ionizing radiation (X-rays, gamma rays) Breaks in single strands Breaks in double strands May result in deletions, insertions

DNA REPAIR Mutations are rare –Many errors are automatically corrected by DNA Polymerase’s spell checking abilities Mutations in genes for DNA repair enzymes are particularly problematic –Increase mutations

NORMAL DNA REPAIR Proofreading is always happening –DNA Polymerase detects error during synthesis –Backs up, excises wrong base, and continues –Relatively accurate Mismatch repair is completed –Recognizes mismatch if DNA polymerase misses it –Cuts out incorrect segment –Fills in gap correctly –DNA ligase joins the segments –Relatively accurate