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Lecture Notes 12-24.docx

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Western University
Biology 1001A

Lecture 12October22121032 AM Inheritance in Populations IS Outcomes1 strategy to distinguish between a phenotype that results from codominance relative to incomplete dominance2 characteristics that identify a pleiotropic allele3 conditions under which Hardy Weinberg Equilibrium is possible in a population Lecture Outcomesgeneral pathway of eukaryotic membrane protein productiongeneral physiology of skinhair pigmentationcharacteristics of dominant alleleswhich allele in a heterozygote is dominant given the biochemical mechanism of action of allele productsfactors that affect how allele frequencies change over time in a populationallele frequencies p and q given genotypic frequenciesfunction of various MC1R allelesCQ Which of the following is a true characteristic of dominant allelesThey are the most evolutionarily fit alleles1They are the most common alleles in a pop2They inhibit the expression of recessive alleles3They determine the phenotype of heterozygotes1Ans probably 4 only ScenarioPutting only black pigs b and breeding them on left side only brown pigs w on rightQ If you mated a purebreeding black pig with a purebreeding brown pig what would the piglets look likeAns All black this is F generation1 Q If crossed two F generation piglets together what would the F generation look like12Ans blacks and browns 31black allele is dominant over brownmelanin black and redyellow for skin colour produced by melanocytes packed with melanosomes with melanin and export it to skin cells for pigmentation MC1R normally sits in membrane and makes black melanin with high cyclic AMP levels in response to hormones cyclic AMP level can fall and red melanin is produced instead MC1R W allele can make black or red melanin MC1R B allele has cyclic AMP level high all the time black melanin some brown W alleles some black alleles in a cell alleles are in homologues in DNA in nucleus alleles get transcribed and spliced transcripts leave nucleus and attract attention of ribosomes ribosomes take transcripts to ER transcripts translated on the ER packaged to vesicles that go to golgi then into new vesicles that send those proteins to cell membrane receptors on the surface of the cell two different kinds because of two different allelesblack allele is on all the time even though brown allele is sometimes off cyclic AMP is always on for black allele this is dominance dominance occurs because of the interaction of the gene products biochemistry dominant allele never inhibits the recessive allele the allele that is on all the time determines the phenotypered allele is off all the time in red homozygotes cyclic AMP levels are always low always making red melanin thus pigs are always redgenetics of familiesgenetics of populations CQ If we start with a dominant allele that is common and a recessive allele that is rare what will eventually happenAns The dominant allele will reach 075 recessive 025abundance of brown pigs B common allele some red pigs R rare allele allele frequencies do not change abundance of red pigs R rare allele some brown pigs B common allele allele frequencies do not change THUS in a large population in the absence of selection starting allele frequencies determine future allele frequenciesapplying Punnett squares to populations use product rule to predict offspring genotypes if we know the starting allele frequencies HardyWeinberg principles CQ What if a population contains many allelesB p03 W q03 and R r04How many possible genotypes are thereAns 6Lecture 13October24121032 AM Selection and Fitness IS Outcomes1 Meaning of deme population allele frequency genotype frequency2 Allele frequencies in a population given the genotype frequencies3 Genotype frequencies in the next generation given the allele frequencies and assuming HardyWeinberg equilibrium4 Assumptions of HardyWeinberg equilibrium Lecture Outcomesconditions necessary for HardyWeinberg equilibriumwhether a population is in HWE given observed genotype or phenotype frequencieseffect of selection on changes in allele frequencyrelative vs absolute fitnesshow to calculate relative fitnesshow to quantify strength of selectionrelationship between dominancerecessiveness of alleles and response to selectioneffect of heterozygote advantage on genetic variationwhy the amount of genetic variation in a population is importantdifferent types of selection stabilizing directional and their effect on genetic variation Hardy Weinberg Principlerecessive alleles dont automatically die out dominant alleles arent extremely superior CQ If this population is in HardyWeinberg equilibrium at MC1R what percent of pigs are genotype WRAns 024 012 qr from Wmom Rdad 012 from Wdad Rmom
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