7.03 Final Exam with Solutions

7.03 Final Exam with Solutions NalTle 1 Consider an autosomal allele in rabbits that causes extreme nearsightedness homozygous and that causes partial nearsightedness when heterozygous. Two populations of rabbits are tested for nearsightedness and the frequencies populations of rabbits with vision problems are given below. Population A Extremely nearsighted 0.18 Partially nearsighted 0.24 Population B 0.09 0.42 (a 5pts) Is population A in Hardy-Weinberg equilibrium? Circle the correct answer. Is population B in Hardy-Weinberg Circle the correct answer. (b 5pts) equilibrium? within these Yes ('No-') Y(_) No Rabbits from the two populations are mixed in equal numbers. After one generation of random mating within this new population extremely nearsighted _._ when : and partially nearsighted 2_ 0.3_0,{ what will the frequencies rabbits be? - 0.% Extremely nearsighted Partially nearsighted 2 of Naine Question 1 continued A population of rabbits is in Hardy-Weinberg equilibrium for the nearsightedness allele until a road is built through their territory putting the nearsighted rabbits in grave danger. We will consider two possible modes of selection now imposed on the rabbit population. Mode 1: reproduce. Extremely nearsighted rabbits are always killed by cars before they Partially nearsighted and normal rabbits are essentially never hit by cars. Mode 2: Both extremely nearsighted and partially nearsighted rabbits have a 20% chance of being killed by a car before they reproduce. Rabbits with normal eyesight are essentially never hit by cars. (c 10pts) If the frequency of the nearsightedness allele is 0.1, which mode of selection will drive down the allele frequency faster in the first few generations after the road is built? f_10 de 2_ io_s = "_Z_ + _ " 3 D"-s Name 2 Consider two temperature sensitive mutations in yeast, tsml and tsm2. When a tsml strain is crossed to a tsrn2 strain the diploids are not temperature sensitive. When these diploids are sporulated, tetrads of three types are found. In the table below tsmeans temperature sensitive and ts+ means wild type growth. TypeI ts+ T_vpe II ts+ T_vpe III ts- tS+ ts- tS" tS" tS" ts- tS" tS" ts" N ::) --r (a 7pts) From 50 tetrads; 2 are type I, 12 are type II and 36 are type III. What is the distance in map units between tsml and tsm2? (b 8pts) If the strains from this cross were not ordered into tetrads, the map distance between the two mutations could still be calculated. Using the standard def'mition of map units and the fraction of the 200 strains from the cross that are ts +, calculate the distance between tsml and tsm2. z/. so (c 5pts) Say you need a strain that has both tsml and tsm2 mutations. Without any further testing, which of the strains from the tetrad analysis would you pick? (d 5pts) Four strains from one of the type IItetrads have the following properties: Strain 1: Strain 2: Strain 3: Strain 4: Mating type ct, ts+ Mating type (x,tsMating type a, ts" Mating type a, ts" Strain 2 is crossed to strain 3 and the resulting diploid is ts+. Which of these four strains has both the tsml and tsm2 mutations? 4 Nafne 3 (a 10pts) The proC gene lies very close to the lac operon on the E. coli chromosome, proC shows 90% cotransducfion with a lad" nonsense mutation and 80% cotransduction with a laeZ" nonsense mutation. In a transduction experiment, phage are grown on a proC +, laeI', lacZ" host. The resulting transducing phage are used to infect a proC', lad +, laeZ + recipient and proC + transductants are selected. Three phenotypic classes are found among the proC + transductants: regulated expression of [5galactosidase, constitutive expression of [5-galactosidase, and no [5-galactosidase expression. Give below the expected frequencies of each of the three phenotypic (assume no quadruple crossovers). Reg01ated expression ."_ , _._oC _ q, (b 10pts) Constitutive __expressi°n classes NO expression _ _- 3 / _-__ _ The proB gene is also closely linked to the la¢ operon. In a transduction experiment, phage are grown on a proB +, lacI', laeZ" host and are used to infect a proB', lad +, lacZ + recipient. Of the proB + transductants, most show either regulated expression or no expression of _galactosidase. Transductants that show constitutive [5- galactosidase expression are extremely rare. Draw a map of the lac region showing the relative order of the proC, proB, lad and lacZ genes (don't worry about distances). ,_ 5 Name 4 Below is the pedigree of a family in which a rare, fully penetrant neurological disorder is inherited. A particular DNA probe is used to analyze a restriction enzyme fragment digest from each of the members of the family. Restriction fragments from each individual are found to hybridize with the probe as shown below. (circle female, square male, f'dled afflicted.) Generation '@ , ,, 4KI III 11 '.... 5kb :.... ! I ---- -,-- -,"- 2kb ! I1-1 11-2 I-1 I-2 il-3 II1-1 111-2 111-3111-4 11-4 (a 2pts) What is the mode of inheritance of this disorder? (b 3pts) What is the size of the DNA fragment that is linked to the mutation responsible for the disorder? (c 5pts) Identify all unaffected members of the family who probably are carriers.. i-9_ 7_-3 _L-( (d 5pts) Could any other unaffected member(s) have inherited the mutation? Explain briefly! 6 6 (12pts) individuals You have two true breeding brown-eyed stocks of Drosophila. When from either stock are crossed with red-eyed wild-type flies you have a 3: I ratio of brown to red-eyed phenotypes in the F2 generation. When individual flies of the two brown-eyed stocks are crossed with each other, all of the F1 flies are brown-eyed. For each question below, circle the T preceding each statement that is true and the F preceding each statement that is false. More than one statement may be true. T_ F F 1. The mode of inheritance is most likely recessive. 2. The mode of inheritance is most likely autosomal. T (_) 3. The mode of inheritance could include two genes. F 4. The F2 progeny from the cross between the brown-eyed stocks could be all brown- eyed. T (_) 5. The F2 progeny from the cross between the brown-eyed stocks could display a 1:1 ratio of brown eyed to wild-type phenotypes. T @ 6. The F2 progeny from the cross between the brown-eyed stocks could display a 15:1 ratio of phenotypes. 7 NaiI2e 8 You have a strain of Drosophila homozygous for an autosomal recessive mutation (purple (pr)) that causes a recessive brown eye color. In your pr strain you f'md a male fly which has the wild-type eye color red. You assume that this is a suppressor mutation which you call sup-1. You cross the red-eyed, sup-1 male with females from the pr strain and f'mdthat all female progeny are red-eyed and all male progeny have brown eyes. (a 3pts) Is the suppression caused by the sup-1 mutation recessive or__ (b 3pts) Is sup-1 autosomal o@ (c 8pts) Determine the phenotypic ratio of brown and red-eyed females and males in the next (F2) generation. (Be sure to specify ratios among males and females!) brown females red 1 I t ] males You are given a second red eyed stock that is homozygous for pr. Assuming that this is a new suppressor mutation, you call this mutation sup-2. You cross females from this strain to the sup1 red-eyed male from (a). In the F1 progeny all females have red eyes and all males have brown eyes. (d 8pts) Determine the phenotypic ratio of brown- and red-eyed females and males in the next generation (F2). brown red females 3 -_ males 3 5