7 03 Genetics Fall 2004 Massachusetts Institute of Technology Professor Chris Kaiser Professor Gerry Fink Professor Leona Samson 1 1 Consider an autosomal recessive trait that occurs at a frequency of 10 6 in a specific population that is at Hardy Weinberg equilibrium ie random mating is occurring When answering the following parts show all of your calculations a 7 pts Draw a pedigree below that shows a mating between two relatives that would correspond to an inbreeding coefficient that equals 0 007813 Denote the mating between relatives with a double bar connecting the two related parents Start your pedigree with the common pair of ancestors and end your pedigree with the two related parents who are mating b 8 pts Now say that all matings in Generation X of the given population are either between unrelated individuals or have the same inbreeding coefficient as the mating described in part a If the incidence of the trait in Generation X 1 increases to a 6 frequency of 2 X10 what percentage of matings in Generation X must have been between unrelated individuals 2 c 4 pts Now assume that this autosomal recessive trait causes lethality in childhood If a constant percentage of matings are between related parents for many generations would you predict that q would increase OR decrease d 9 pts A constant percentage of matings has occurred between related parents for many generations and yet you find experimentally that q has not changed Of the three choices below circle ALL that could potentially act against the effect you chose in part c in order to keep q constant Explain in one sentence why you chose or did not choose each option Choice A migration Choice B heterozygote advantage Aa over AA Choice C mutation 2 You are studying regulation of the Wrm1 gene a yeast gene that is expressed in response to heat You isolate a wrm1 lacZ strain that expresses galactosidase when Wrm1 is normally expressed which is at 36 C but not at 24 C You use this wrm1 lacZ strain to perform a genetic screen looking for mutants that do not properly regulate expression of Wrm1 In your screen you isolate a series of mutant strains that either show constitutive or uninducible expression of wrm1 lacZ Your results indicate that the following is the correct pathway for regulation of Wrm1 expression Note that WrmY and WrmX are on the same chromosome and that WrmX WrmZ and Wrm1 are all on different chromosomes heat WrmY WrmX WrmZ Wrm1 3 One of the mutant strains you isolate contains a mutation called WrmX which is in the coding region of WrmX You mate a WrmX wrm1 lacZ haploid strain to a wrm1 lacZ haploid strain The resulting diploids are white on X gal plates that are incubated at 24 C and are blue on X gal plates that are incubated at 36 C a 3 pts Classify the WrmX mutation as constitutive OR uninducible b 3 pts Classify the WrmX mutation as dominant OR recessive c 3 pts Classify the WrmX locus as cis acting OR trans acting with respect to Wrm1 You next isolate a mutant strain containing a mutation called WrmY which is in the coding region of WrmY You mate a WrmY wrm1 lacZ haploid to a wrm1 lacZ haploid The resulting diploids are white on X gal plates regardless of the temperature at which the plates are incubated d 6 pts Classify WrmY by the type s of mutation it could be with respect to Wrm1 Your choices are repressor activator UAS URS super activator super repressor dominant negative repressor dominant negative activator 4 You create diploid yeast by mating WrmX WrmY wrm1 lacZ haploid yeast to wrm1 lacZ haploid yeast Sporulation of these diploids yields two types of tetrads and you correctly conclude given the number of each type of tetrad that the WrmX and WrmY loci are linked at a distance of 2 22 cM e 14 pts Depicted below are the two types of tetrads that resulted when you sporulated the above diploids For each type of tetrad state how many you found of that tetrad out of a total of 90 tetrads classify the tetrad as PD NPD or TT and color in all of the spores that would be blue on each of the following Petri plates Tetrad Type A Number of these tetrads out of a total of 90 Classification of these tetrads PD NPD or TT Color in the spores that would be blue in color when growing on the following plates X gal 24 C X gal 36 C NOTE that the two plates are replicas so the top spore on the left plate has the same genotype as the top spore on the right plate Tetrad Type B Number of these tetrads out of a total of 90 Classification of these tetrads PD NPD or TT Color in the spores that would be blue in color when growing on the following plates X gal 24 C X gal 36 C 5 3 You are mapping a certain disorder that is caused by an allele at the N locus You suspect that the N locus is linked to SSR112 on human chromosome 17 You analyze the following family for these two loci You will fill in the charts below in subsequent parts of the problem Individual 1 Individual 2 A allele B allele C allele D allele maternally inherited allele at SSR112 paternally inherited allele at SSR112 maternally inherited allele at the N locus paternally inherited allele at the N locus maternally inherited allele at the N locus paternally inherited allele at the N locus IF the condition is autosomal recessive parts a and b Individual 2 is nn IF the condition is autosomal dominant parts c e Individual 2 is Nn Answer parts a and b as if the disorder is autosomal recessive and caused by the n allele so that Individual 2 is nn a 9 pts Fill in the upper four rows of the chart using autosomal recessive inheritance for the disorder Then answer below which parent s alleles will you follow to correctly calculate a LOD score between the N locus and SSR 112 Individual 1 or 2 6 SSR 112 b 3 pts Draw all phases of the parent you chose in part a with respect to SSR 112 and the N locus that are possible given everything you know about that parent Make sure to draw the phases using the proper notation Answer parts c through e as if the disorder is autosomal dominant and caused by the N allele so that Individual 2 is Nn c 6 pts Fill in the lower two rows of the chart using autosomal dominant inhertance for the disorder Then answer below which parent s alleles will you follow to correctly calculate a LOD score between the N locus and SSR 112 Individual 1 or 2 d 3 pts Draw all phases of the parent you chose in part c with respect to SSR 112 and the N locus that are possible given everything you know about that parent Make sure to draw the …
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