BIOL 1411 1st Edition Lecture 28 Outline of Last Lecture I Developmental Genetics Mutations Outline of Current Lecture II Mutations Lecture Mutations Changes at the level of DNA sequence o point mutation results from the gain loss or substitution of a single basepair of DNA o Small indels insertions or deletions of a few to hundreds of basepairs of DNA o Chromosomal mutations more extensive may change the position of genes or cause multiple genes in a DNA segment to be duplicated or lost Mutation change in DNA sequence o DNA is a stable repository for genetic information Semiconservative replication maintains an old copy of each base sequence in each newly replicated molecule o But changes in DNA sequence occur both spontaneously and through external factors What are mutations o Spontaneous mutations several mechanisms that can change DNA Bases can have differentstructures may form tautomers a rare tautomer can pair with the wrong base Chemical reactions may change bases o Induced mutation caused by mutagens Chemicals can alter bases Some chemicals add other groups to bases DNA polymerase will then add any base there o Radiation damages DNA Ionizing radiation such a X rays creates free radicals highly reactive can change bases and break sugar phosphate bonds UV radiation is absorbed by thymine causing it to form covalent bonds with adjacent nucleotides disrupts DNA replication o Measuring the mutation rate These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Haploid Human Genome 3 000 000 000 bp 35 new mutations inherited from each parent 70 total in each person born 130 million births each year so on average each position in the human genome have 1 new variant produced annually o Cost and Benefits of Mutations Costs Some germ line and somatic cell mutations are harmful or lethal leading to genetic diseases and cancer Mutations commonly responsible for recessive mendelian traits occurred long ago exist as genetic load Benefits Provide the raw material for evolution in the form of genetic diversity Evolution would not be possible without mutation Inherited PKU in humans o Genetic mutations may make proteins dysfunctional o Phenylketonuria PKU results from an abnormal anzyme phenylalanine hydroylase normallycatalyzes conversion of dietary phenylalanine to tyrosine o The common PKU allele produces an abnormal enzyme with tryptophan instead of arginine at position 208
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