Exam Answers Biology 20 Sept. 20, 2006 Name: Section:. (5 points) Circle the answer that gives the maximum number of different alleles that might exist for any one locus in a normal mammalian cell. A. D. 4 B. 2 E. 8 C. 3 F. Many 2. (6 pts) Suppose you want to determine the genotype of a mouse ( Pinky ) who has the dominant phenotype at some locus. (as opposed to having the recessive phenotype at this locus) A. What do you call the kind of cross you must do? (one phrase) A testcross B. What must be true (genotypically) of the mouse that you mate with Pinky? That mouse must be homozygous recessive. C. What are the phenotypes and ratios that you would expect in offspring from this mating if Pinky is heterozygous? ½ the mice will have the dominant phenotype and ½ the mice will have the recessive phenotype. 3. (9 pts) Consider three gene pairs Aa, Bb, and Cc, each of which assorts independently and affects a different trait. The upper case represents a dominant allele and the lower case represents a recessive allele. Give the probability for obtaining each of the following: A. an AaBb genotype from a cross between parents who are AaBb x Aabb ½ x ½ = /4 B. an AabbCC genotype from a cross between parents who are AaBbCc x AABbCC ½ x ¼ x ½ = /6 C. an a, b, c phenotype from a cross between parents who are AaBbCC x AabbCC Probability of c phenotype is 0, so answer is 0
4. (6 pts) The cells in the following figure were all taken from the same Andean rose rat. Identify the cell division (mitosis, meiosis I, or meiosis II) AND the phase for each cell (prophase, metaphase, etc.). anaphase of meiosis II metaphase of mitosis prophase of meiosis I 5. (8 pts) What is the sex of an XXY individual in humans? Male What is the sex of an XXY individual in Drosophila (fruit flies)? Female 2
6. (0 pts) The students in a Biology 20 genetics class did a cross by breeding tall cougar daisies with short cougar daisies and analyzed the progeny. They believed that they were looking at one trait in which the short daisies were homozygous recessive and the tall daises had at least one dominant allele. 60 of the progeny were tall and 40 were short. They did a chi square analysis to determine if these results supported their hypothesis. Answer if 3: expected if : expected A. What were the total number of progeny observed? 00 00 B. How many degrees of freedom are there in their analysis? C. What is the value for Chi-squared (X 2 )? 2 4 NOTE: There was a problem with the way I worded this question versus the way I described it when there were questions during the exam, so we are giving credit for this question, whether you did it as if it is a test-cross (as worded here), or as one of Mendel s monohybrid crosses: (TT x tt = P, giving rise to Fs that are all Tt, which, when crossed would be predicted to give a 3: phenotypic ratio). The only requirement was that you were consistent throughout your analysis, ie, you did an analysis with expected ratios of either : or of 3:. If expect 3: (Tt x Tt), P is P < 0.005 If expect : (T_ x tt), P is between 0.05 & 0.0 D. Circle the correct value for P: P > 0.05 P is between 0.05 & 0.0 P is between 0.0 & 0.005 P < 0.005 E. Are the results consistent with their hypothesis (yes or no)? _No, by either scenario 7. (8 pts) What do we mean when we say that epistasis is occurring? Do not use examples in answering this question. (one sentence only) One gene is masking the expression of another gene. (must be clear that you are referring to at least 2 different loci.) 3
8. (2 pts) The pedigree below is for a rare autosomal recessive genetic disease (d) in which all the individuals with the disease are shaded. The genotype is given for some of the individuals who do not have the disease. A. Next to each of the 4 individuals with an arrow pointing to them write all of the possible genotypes they could have. B. Inside of the circle or square for each of those 4 individuals, give the probability that they are a carrier. C.?? If Bob and Julie are thinking about having another child. What is the probability that their child will have the disease? /4 DD DD Dd Dd DD DD or Dd /2 Dd 2/3 Dd or DD 9. (5 pts) In order to determine if two independently isolated mutations from different individuals are at the same locus or at different loci, which test would you perform? A. a test cross B. an epistasis test C. a complementation test D. a dihybrid test E. a biochemical test 0. (4 pts) All the ABO blood type alleles map to a single gene locus. True or False? 4
. (2 pts) A father has hemophilia B, an X-linked recessive disease. He and his wife, who carries no allele for the disease, have a boy and a girl. A. What is the probability that the girl will carry an allele for the disease?.0 B. What is the probability that the boy will have the disease? 0 C. If their girl eventually marries a normal man (sometimes they re hard to find!) and they have a son, what is the probability that this son will have hemophilia B? /2 2. (5 pts) A child has type AB blood, and her mother has type A blood. Give all possible genotypes and blood types for the father of this child. (Child must be i A i B. The Mother contributed the i A allele, so...) The father, who contributed an i B allele, can have either type AB blood (genotype i A i B ), or type B blood ( genotype i O i B or i B i B ). 3. (0 pts) In the following cross between AaBb heterozygotes (AaBb x AaBb), the biochemical pathway given below also shows the colors of the compounds produced. What is the phenotype you would obtain for each of the genotypes listed below, AND what are the phenotypic ratios you will derive from this cross. Assume that the phenotype is white unless otherwise indicated. A- Blue B- Green Blue Genotype: A-B- A-bb aab- aabb Phenotype: green blue blue white Phenotypic ratios (include the phenotype with each number): 9 green: 6 blue: white 5
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