Week 4 Bio Notes
Week 4 Bio Notes Biol 180
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This 8 page Class Notes was uploaded by Nikki Hovland on Thursday October 22, 2015. The Class Notes belongs to Biol 180 at University of Washington taught by Scott Freeman in Summer 2015. Since its upload, it has received 60 views. For similar materials see Introductory Biology in Biology at University of Washington.
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Date Created: 10/22/15
INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 Week 4 Notes After Exam 1 Lecture 12 The gene mutation and alleles DNA and RNA both consist of sugarphosphate backbones created by phosphodiester linkages type of bond number of purines number of pyrimidines in DNA number of thymines and adenines are equal T and A have 2 H bonds number of cytosines and guanines are equal C and G have 3 H bonds Watson and Crick discovered DNA base pairing and the double helix structure DNA contains info required to copy itself enzymes separates double helix free floating deoxyribonucleic acids form complimentary Hbonds with base pairs to template strand DNA is organized stable structure so it can t be a catalyst Beadle and Tatum s research the idea was that they could use a knockout gene damaged gene so it can t express its function and observe to see what changes in phenotypes there are to match genes to their functions knock out gene or lossoffunction allele alleles that do not function at all onegeneoneenzyme hypothesis based on the knock out mutant tests claims that each gene makes one enzyme self explanatory Crick proposed that different combinations of bases specify the 20 different amino acids gene section of DNA that influences the phenotype for a particular trait structural codes for RNA protein that functions regulatory responsible for expression of gene offon etc INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 species like humans and chimps are different because of different regulatory gene sequences different genes are expressed in different cells DNA builds or regulates differences between copies of same genes are alleles variation of proteins usually we are discovering new alleles not new genes they have always been there mRNA short lived molecule that carries info from the DNA in the nucleus to the ribosomes where its used to make proteins RNA polymerase an enzyme that makes RNA according to the information encoded in the DNA central dogma the flow of information in cells DNA gt RNA gt amino acidsproteins NOTE sometimes info turns back into DNA from RNA transcription DNA gt RNA through help of RNA polymerase translation RNA gt proteins takes place in ribosomes DNA gt transcription gt mRNAgt translation gt proteins info storage info carrier active cell machinery genotype is a product of the DNA sequence phenotype is a product of the proteins that are created triplet code three bases codon that each are translated into a certain amino acid the genetic code is redundant unambiguous each codon corresponds to one amino acid not more than one does not overlap INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 almost universal all organisms have either DNA or RNA or both conservative the first 2 bases are almost always the same for several different codons to help prevent drasticsevere mistakes mutation any permanent change in the DNA changes genotype and may OR may not change phenotype also creates new alleles three different types beneficial increases fitness neutral has no effect on fitness deleterious lowers fitness if the genotypes changes we don t always know if the phenotype changes depends on if the proteins that are produced are affected or not types of mutations silent mutation point mutation that does not change the amino acid sequence point mutation single base change usually because of mistake in making or repairing DNA frameshift single addition or deletion of a base that changes all of the following codons and what amino acids are produced nonsense codon for an amino acid changes to a stop codon and results in non functional protein chromosomes can have mutations too inversion segment breaks off and flips and then reattaches translocation segment detaches and the rejoins a different chromosome segment is lost and broken off uplication extra copies of a segment are present INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 LECTURE 13 Sources and Extent of Genetic Variation mutation any change in organisms DNA Layarckian inheritance doesn t work because the environmentgaining a trait does not change genotype ONLY MUTATION DOES mutation is RANDOM PROCESS random with respect to fitness most mutations are neutral or deleterious most organisms already adapted so new mutations often do not increase fitness mutation is CONSTANT and is always introducing new alleles genotype always changes but may not always show in phenotype occurs during DNA synthesis and repair mutations create heritable variation since the changes are passed on to offspring polygenetic inheritance many genes contribute to a particular phenotype 4 sources of genetic variation mutation creates variation by introducing NEW alleles occurs during interphase DNA replication due to mistakes in copying DNA independent assortment creates variation by random combo of mom and dad chromosomes occurs in metaphase 1 of meiosis of possible combinations 2An crossing overgenetic recombination creates variation WITHIN chromosomes occurs in prophase 1 of meiosis outcrossing not selfing creates variation by combining alleles from two DIFFERENT individuals and occurs during fertilization asexual reproduction when offspring are produced without using and fusing gametes together like mitosis in eukaryotes almost NO GENETIC VARIATION INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 sexual reproduction producing offspring as a result of making and fusing gametes meiosis changes in chromosomes through meiosisfertilization are very important because it contains all of the hereditary info from parents 1 chromosome unreplicated 1 DNA strand replicated2 DNA strands genetic variation promoted through crossing over and separating homologs independent assortment is vital to increasing variation in offspring increases variation via new assortments of chromosomes WWW combinations of alleles crossing over also increases genetic recombination within a chromosome these processes make each gamete unique self fertilization two gametes from one individual forms an offspring offspring are likely to be very different from parent outcrossing gametes from diff individuals form offspring this is a heritable trait down syndrome results from mistake in meiosis resulting in trisomy 3 bodies 3 of one type of chromosome instead of 2 in this case chromosome 21 nondisjunction an error in meiosis in which the homologs in meiosis 1 or sister chromatids in meiosis 2 do not separate and move to one side together often leads to trisomy 2n1 or monosomy 2n1 in resulting cells mistakes in meiosis are common and often lead to miscarriages in humans aneuploid without form cells with too few or too many chromosomes trisomies are often seen in sex chromosomes and in the smaller chromosomes asexual reproduction is much more efficient than sexual reproduction all offspring are child bearing vs only females in sexual reproduction Why sexual reproduction Purifying Selection Hypothesis INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 BUT asexual reproduction with deleterious alleles dooms ALL offspring while sexual reproduction often leads to some individuals without the bad allele natural selection against deleterious lower fitness alleles is purifying selection reduces the advantage asexual reproduction has in numbers Changing Environment Hypothesis offspring clones are not very likely to survive well if their environment changes if offspring are genetically varied it is more likely that some of the offspring will have a combination of alleles that allows them to be protected against a strain of disease while clones would likely all die LECTURE 14 Hardy Weinberg Principle 4 processes of evolution natural selection increases frequency of particular alleles that are advantageous increase fitness genetic drift randomly changes the frequencies of alleles increase or decrease aness gene flow individuals from a different population mate with another population introducing new alleles and changing frequencies mutation random changes in DNA that creates new alleles that may increase or decrease fitness or have no effect Hardy Weinberg principle mathematical null hypothesis model for the theory of evolution and the four different processes assumes mating is random if you add new alleles to the population you change the frequencies and VIOLATE H W principle makes two key claims 1 frequencies of A and a alleles are denoted by p and q so therefore the genotypes of AA pA2 Aa 2pq aaqA2 from one generation to the next thus p q 1 ALWAYS the frequency of the A allele plus the a allele should1 INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 o 2 allele frequencies do not change over time as meiosis and random recombination occurs from generation to generation UNLESS another factor affects the frequencies and evolution occurs gt evolutionary mechanism occurs gene pool a collection of all of the alleles in a population generation Assumptions needed to be met for HardyWeinberg model random mating no sexual selection no natural selection all individuals survive no matter genotype no genetic driftrandom changes in allele frequencies no gene flow no new individuals introduced no mutation principle acts as null hypothesis when we want to test one of evolutionary processes LECTURE 15 Patterns of Natural Selection essentially the alleles that lead to favorablemore advantageous traits in phenotypes increase in frequency while others less beneficial decrease in frequency this is a violation of HardyWeinberg model and evolution occurs genetic variation the different frequencies of alleles present in a population lack of variation is BAD directional selection changes average value of trait the average phenotype in the population moves in one direction on a graph the mean and bell curve moves right or left REDUCES variation in a population over time favored allele frequency approaches 1 when disadvantageous alleles decline in frequency purifying selection stabilizing selection reduces variation in a trait no change in average trait over time INTRODUCTORY BIOLOGY 180 Thursday October 22 2015 on a graph the bell curve gets skinniernarrower and the mean value does not move disruptive selection increases variation in a trait OPPOSITE OF STABILIZING eliminates alleles near the average value phenotype and favors the extreme phenotype alleles overall variation remains the same or increased occurs when the average phenotype is no longer favored for environment helps form new species leads to speciation once the extremes become more and more favored over time balancing selection maintains variation in a trait a single allele has the most advantagemost favored this occurs when heterozygote advantage heterozygotes have higher fitness than homozygotes environment changes over time leading to the favoring of different alleles at different timesplaces variation maintained or increased frequency dependent selection some alleles are favored when they are rare but are not favored when they become more common like the skin coloring of fish predators look for more common colors so rare alleles are favored leads to increased or maintained variation