1 Biol 321 Spring 2013 Midterm Exam [90 points] NAME________________________________________ • REMEMBER: carefully inspect problems and pay attention to detail! • YOU ARE NOT ALLOWED TO USE CALCULATORS OR CELL PHONES DURING THIS EXAM or to send or receive signals of any kind • READ EACH QUESTION CAREFULLY BEFORE ANSWERING. 1. (3 pts.) Marfan’s syndrome is an autosomal dominant disorder of connective tissue that is manifested in the ocular, skeletal and cardiovascular systems. This syndrome shows great clinical variability but all individuals with the mutation show some symptoms. In addition, all individuals studied so far with Marfan syndrome have a mutation in the same gene. Choose the best restatement of this information. a. Marfan syndrome is pleiotropic and incompletely penetrant. b. Marfan syndrome is pleiotropic and variably expressed. c. Marfan syndrome is polymorphic and variably expressed. d. Marfan syndrome is pleiotropic, variably expressed and genetically heterogeneous. e. Marfan syndrome is genetically heterogeneous and variably expressed. f. None of these statements is corrrect. Problems (pts.) Score 1 ( 3 pts.) 2 & 3 ( 10 pts.) 4 (18 pts.) 5 ( 18 pts.) 6 (6 pts.) 7 ( 12 pts.) 8 partsA&B (13 pts.) 8 part C ( 10 pts.) Total out of 1002 2. (6 pts.) Examine the diagram to the right . Each line represents a single molecule of double-stranded DNA, which will segregate as indicated. The dotted line indicates where the cytoplasm will be divided during cytokinesis. Fill in the 2 blanks for parts a & b. a. This diagram is consistent with mitosis in a 1 n = 3 organism b. This diagram is consistent with Meiosis II in a 2 n = 6 organism c. If the genotype the organism in (b) is AaBbDD, what fraction of the all of the Meiosis II divisions occurring in the gonad of the organism would resemble the diagram? [Ignore complications from crossing over events & no explanation needed.] Circle the correct answer: (i) 1.0 (ii) ½ (iii) ¼ (iv) 1/8 (v) not possible to determine from info given 3. (4 pts.) Recall our discussion of the evolution of the Y chromosome. Circle True or False. 1 pt if no explanation required. 2 pts if explanation required. True Despite its name, the differential region of the Y chromosome contains genes that are also present on the X chromosome. False The present day Y chromosome is a decayed version of its former self because mutations in the pairing region cannot be purged by recombination with a homolog. [By definition, the pairing regions of the X and Y chromosomes carry the same genes and therefore synapsis and cross-over during prophase of the first meiotic division.] True The evolution of the mammalian Y reflects an evolutionary trade-off between erosion (decay) of gene function versus ensuring that the Sry gene and genes required for male fitness “stayed together.” One sentence explanation The loss of the ability of the evolving ancestral Y chromosome to cross-over with the ancestral X chromosome resulted in the loss of most of the genes once carried in the region BUT allowed the Sry gene to be inherited as a (non-recombinant) unit along with genes required for sperm formation (and not represented elsewhere in the genome).3 4. (18 pts.) Revised from your assignment set. You have a true-breeding wild-type strain of fish. A colleague of yours gives you a mutant fish that is naked (no scales). You do the following crosses: Parental naked X wild-type scales (scales all over) Nn LL  (truebreeding) nn ll F1 1/2 linear scales (one line of scales) nn Ll 1/2 naked Nn Ll F1 Cross A F1 naked X F1 naked Nn Ll Nn Ll  F2 12/16 naked N- -- (9/16 N- L- 3/16 N- ll) 3/16 linear nn L- 1/16 wild-type nn ll F1 Cross B F1 linear X F1 linear nn Ll nn Ll  F2 3/4 linear nn L- 1/4wild-type nn ll F1 Cross C F1 linear X F1 naked nn Ll Nn Ll  F2 ½ Nn naked ¾ L- linear ½ nn has scales ¼ ll wildtype (scattered) OVERALL ½ (4/8) Nn -- naked 3/8 nn L- (linear) 1/8 nn ll (scattered) A: Define allele symbols. Clearly indicate dominance and describe (in a couple of words) the trait that each gene controls. N gene controls the production/development of scales N= no scales n = scales L gene controls the scale pattern L = linear (one line of scales) l =wildtype (scattered) B What type of gene interaction is operating here? Use proper terminology (no explanation required) dominant epistasis the N- genotype is epistatic to the L gene C. WRITE OUT GENOTYPES FOR EACH CROSS. For the cross C predict the the F2 genotypes and phenotype (indicate ratios for the latter).4 5. (18 pts.) Revised from the S12 midterm. PART A (5 pts.) Examine Nature News blurb on pg 2 of the Info/Data sheet. The researchers isolated 7 different true-breeding mutant strains showing increased alcohol tolerance compared to the wildtype strain. Examine this first series of crosses and clearly & explicitly state all conclusions below each set of observations For mutant lines #1-5, reciprocal crosses between true-breeding wild-type (intolerant) and mutant (tolerant) lines produced male and female progeny with the wildtype phenotype. The mutant alleles are recessive to wild-type for each of these strains The genes mutated in these strains are all autosomal Be careful with wording here: traits and alleles show dominance but genes do not. For mutant line #6, when wildtype females were crossed with mutant males, all progeny were wildtype (alcohol intolerant). When the reciprocal cross was performed, all males were mutant and all females wildtype. The gene mutated in this strain is located on the X chromosome and the mutant allele is recessive to the wild-type allele. For mutant line #7, reciprocal crosses between true-breeding wild-type and mutant lines produced male and female progeny that were alcohol tolerant. The mutant allele is dominant to the wild-type allele and the gene mutated in this strain