B250WT2S05 - M .CO 411 MED - PR E BIL 250/P “Genetics”...

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Unformatted text preview: M .CO 411 MED - PR E BIL 250/P “Genetics” 3/24/05 Form 1 OM Exam 2 - PR EME D41 1.C *: The underlined choice is the correct answer. OM Use the following information for questions 1-2. - PR EME D41 1.C A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). As in humans, sex chromosomes determine sex: XX in females and XY in males. D41 - PR EME D41 1.C OM - PR EME P 1.C OM 1. What is the total number of chromosomes present in the cell during metaphase I of meiosis? a. 21 b. 42 c. 84 d. 126 e. 168 D41 1.C OM - PR EME D41 1.C OM 2. What is the total number of chromosomes in a polar body cell from a rat? a. 21 b. 40 c. 41 d. 42 e. 84 A B C d PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM - PR EME D4 11. COM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME 3. The figure shows a chromosomal separation taking place. The letters stand for genes; capital and lowercase stand for different alleles. 2n in this organism is 4. What process is shown? a. anaphase of mitosis b. telophase of meiosis I c. anaphase of meiosis I d. telophase of mitosis e. anaphase of meiosis II A b C d M .CO 411 MED - PR E OM 1.C OM - PR EME D41 1.C 4. While doing field work in Madagascar, you discover a new dragonfly species that has either red (R) or clear (r) wings. Initial crosses indicate that R is dominant to r. You perform two crosses using two different sets of red-winged parents with unknown genotype and observe the following data: Phenotypes 72 red-winged, 24 clear-winged 96 red-winged 1.C OM - PR EME D41 Cross 1 2 - PR EME D41 1.C OM - PR EME D41 What is the most likely genotype for each pair of parents in the two crosses? a. Cross 1: RR X Rr; Cross 2: RR X Rr b. Cross 1: Rr X Rr; Cross 2: Rr X Rr c. Cross 1: Rr X Rr; Cross 2: RR X RR d. Cross 1: RR X RR; Cross 2: RR X RR D41 1.C OM - PR EME D41 1.C OM 5. Codominant alleles are expressed in individuals that are _____________. a. penetrant b. homozygous c. polymorphic d. heterozygous e. mutually exclusive - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME 6. In mammals, the inability to make the pigment melanin results in albinism, a recessive somatic condition. Two normal parents, who have decided to have three children, have a first child that is albino (genotype aa). Determine the following probability that the second and third children are normal. a. 1/16 b. _ c. 1/8 d. _ e. 9/16 PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM - PR EME D4 11. COM 7. Red-green color blindness is X-linked recessive. A woman with normal color vision has a father who is color-blind. The woman has a child with a man with normal color vision. Which phenotype is NOT expected? a. color-blind female b. color-blind male c. noncolor-blind female d. noncolor-blind male M .CO 411 MED - PR E OM - PR EME D41 1.C Use the pedigree for the following three questions. OM I 2 3 4 II 1 2 3 4 5 1 - PR EME D41 1.C OM III - PR EME D41 1.C 1 - PR EME D41 1.C OM - PR EME D41 1.C OM 8. If the pedigree is for an autosomal recessive characteristic, which individuals are definitely heterozygous? a. I-1, I-2, II-2, II-4 and II-5 b. I-1, I-2, I-4, III-1 c. I-1, I-2, II-4, II-5, III-1 d. II-2, II-4, II-5, II-3 e. II-2, II-4, II-5, III-1 OM - PR EME D41 1.C OM - PR EME D41 1.C OM 9. Could the characteristics followed in the pedigree be caused by an X-linked recessive allele? a. Yes, all individuals fit the X-linked recessive inheritance pattern. b. No, the offspring of I-1 and I-2 contradict an X-linked recessive inheritance. c. No, the offspring of I-3 and I-4 contradict an X-linked recessive inheritance. d. No, the offspring of II-3 and II-4 contradict an X-linked recessive inheritance. - PR EME D4 11. COM - PR EME D41 1.C 10. If the characteristic followed in the pedigree is X-linked recessive allele, what is III-1’s genotype? a. hemizygous for a dominant allele b. hemizygous for a recessive allele c. definitely heterozygous d. definitely homozygous dominant e. either heterozygous or homozygous dominant PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM 11. The terms cis and trans describe a. the configuration of alleles on homologous chromosomes. b. the relative position of different loci on the same chromosome. c. the relative position of different loci on different chromosomes. d. the ability of a deletion to uncover a recessive allele. e. the ability to use deletions for mapping genes. M .CO 411 MED - PR E 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM 12. A testcross is performed on an individual to examine three linked genes. The most frequent phenotypes of the progeny were Abc and aBC, and the least frequent phenotypes were abc and ABC. What was the genotype of the individual tested and what is the order of the gene loci? a. Abc / aBC; CBA b. ABC / abc; ACB c. Acb / aCB; ABC d. ACb / acB; BAC e. Abc / aBC; CAB D41 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME D41 13. The following F2 results occur from a typical dihybrid cross: purple: A_B_ 9/16 white: aaB_ 3/16 white: A_bb 3/16 white: aabb 1/16 If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb) what phenotypic ratio is expected in the offspring? a. 1 (white) : 1 (purple) b. 12 (white) : 7 (purple) c. 9 (white) : 7 (purple) d. 3 (white) : 1 (purple) e. 2 (white) : 1 (purple) D41 1.C OM - PR EME D41 1.C OM - PR EME 14. Assume that a dihybrid cross is made in which the genes' loci are autosomal, independently assorting, and incompletely dominant. How many different phenotypes are expected in the offspring? a. 4 b. 16 c. 9 d. 2 e. 3 PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM - PR EME D4 11. COM - PR EME 15. A situation where there are multiple alternative forms of a given gene would be called_______. a. multiple alleles b. alternation of generations c. codominance d. incomplete dominance e. hemizygosity M .CO 411 MED - PR E OM OM - PR EME D41 1.C OM - PR EME D41 1.C 16. A condition in which one gene pair masks the expression of a non-allelic gene pair is called_____. a. codominance b. epistasis c. dominance d. recessiveness e. additive alleles - PR EME D41 1.C OM - PR EME D41 1.C 17. In Drosophila, sex is determined by a balance between the number of haploid sets of autosomes and the number of ________. a. telomeres b. centromeres c. X chromosomes d. Y chromosomes e. nucleolar organizers OM - PR EME D41 1.C OM - PR EME D41 1.C OM 18. Regarding the ABO blood group system in humans, if one of the individual’s parents is type AB, yet this individual expresses the O blood type, it is likely that this individual has the ________ genotype. a. IOIO b. IAIB c. HH d. hh e. Hh OM 1.C Organsm Humans ___?__ Drosophila __?___ - PR EME D41 Sex Chromosome Complement XXY - PR EME D41 1.C 19. Give the sex of these two organisms. Each has a sex chromosome complement of (XXY), and assuming that the autosomes are present in the normal number. - PR EME D4 11. COM a. male; male b. female; female c. female; male d. male; female e. metafemale; metafemale PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM 20. How many Barr bodies would one expect to see in cells of 49, XXXXX syndrome females? a. one b. two c. three d. four e. five M .CO 411 MED - PR E 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM 21. Assume that a Chi-square test was conducted to test the goodness of fit to a 3:1 ratio and a Chi-square test provided a probability value of 0.02. Should the null hypothesis be accepted? How many degrees of freedom would be associated with this test of significance? a. yes, 2 b. yes, 1 c. no, 1 d. no, 2 e. no, 3 1.C OM - PR EME D41 1.C OM - PR EME D41 22. Assuming independent assortment, what proportion of the offspring of the cross AaBbCcDd x AabbCCdd will have the aabbccdd genotype? a. 34 b. 24 c. 1/16 d. 1/64 e. zero OM - PR EME D41 1.C OM - PR EME D41 23. Which of the following is NOT true about sex-linked genes? a. In humans, the term sex-linked usually refers to X-linked characters. b. Fathers pass X-linked alleles to all their daughters, but not sons. c. Mothers can pass sex-linked alleles to both sons and daughters. d. Far more males than females have disorders that are inherited as sex-linked recessives. e. All statements above are true. D41 1.C OM - PR EME D41 1.C 24. Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first child will have hemophilia, if their first child is a boy? What is the probability that their first child will have hemophilia, if their first child is a girl? - PR EME D4 11. COM - PR EME a. 1/2; 1/2 b. _ ; 0 c. _ ; 0 d. _; 1/2 e. 0; 0 PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM 25. Which of the following is NOT true about homologous chromosomes? a. Homologous chromosomes are identical in length. b. Homologous chromosomes share the same centromere locations. c. One of each pair of homologous chromosomes is produced from the other in S phase. d. Homologous chromosomes carry the same sequence of gene sites (loci). e. One chromosome is of maternal origin while the other is of paternal origin. M .CO 411 MED - PR E D41 1.C OM Extra credit questions (one point each): OM - PR EME 26. LeMaire-Adkins et al’s paper “Lack of checkpoint control at the metaphase/anaphase transition : ….” published in “Journal of Cell Biology” concerns - PR EME D41 1.C OM - PR EME D41 1.C a. a mechanism of checkpoint control during mitosis in mammalian females. b. a mechanism of mitotic disjunction in mammalian females. c. a mechanism of mitotic nondisjunction in mammalian females. d. a mechanism of meiotic disjunction in mammalian females. e. a mechanism of meiotic nondisjunction in mammalian females. D41 1.C OM 27. The article “How cells get the right chromosomes” published in “Science” by Bruce Nicklas discovered that PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM - PR EME D4 11. COM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME a. when cell divide, the daughter cells will always get the right chromosomes. b. chance events are not involved in chromosome delivery. c. errors in chromosome delivery are avoided by diverse uses of DNA restriction enzymes during the mitotic process. d. errors in chromosome delivery are avoided by diverse uses of mechanical tension from the mitotic process. e. errors in chromosome delivery are avoided by diverse uses of DNA repair mechanisms during the mitotic process. M .CO 411 MED - PR E OM - PR EME D41 1.C Short answer questions: B 1.C a OM b D41 A - PR EME D41 1.C OM 1. An individual has the genotype shown below. Gene loci (A) and (B) are 15 cM apart. Indicate all the possible gametes this individual can produce, and the proportions of expected progeny genotypes if a testcross is performed on this individual. - PR EME D41 1.C OM - PR EME Answer: AB = 42.5% aB = 42.5% AB = 7.5% Ab = 7.5% - PR EME D41 1.C OM - PR EME D41 1.C OM 2. Dosage compensation in mammals typically involves the random inactivation of one of the two X chromosomes relatively early in development. Such X-chromosome inactivation often leads to phenotypic mosaicism. Assume that black fur in cats is due to the X-linked recessive gene b while its dominant allele B produces yellow fur. A Bb heterozygote is a mosaic called "tortoise shell" or "calico." Using appropriate gene symbols, diagram a mating between a black male and a "calico" female. Give the sex, phenotypes and genotypes of all the offspring. D41 1.C OM Answer: bY x Bb = - PR EME Bb (calico female), bb (black female), BY (yellow male), bY (black male) - PR EME D41 1.C OM 3. Assume that a cross is made between a heterozygous tall pea plant and a homozygous short pea plant. Fifty offspring are produced in the following frequency: - PR EME D4 11. COM 30 = tall 20 = short (a) What frequency of tall and short plants is expected? - PR EME D4 11. COM (b) If one wanted to test the goodness of fit between the observed and expected values, provide a statement of the null hypothesis. ED4 11. COM (c) Compute a Chi-square value associated with the appropriate test of significance. _2 = ∑ (o – e)2/ e (d) How many degrees of freedom are associated with this test of significance? PRE MED 411 .CO MPRE M Answer: (a) 1:1 (25 tall and 25 short) (b) The deviations from a 1:1 ratio (25 tall and 25 short) are due to chance. M .CO 411 MED - PR E - PR EME D41 1.C OM (c) ˜2 = 2 (d) 1 - PR EME D41 1.C OM 4. Cystic fibrosis is an autosomal recessive disorder. A male whose brother has the disease has children with a female whose sister has the disease. It is not known if either the male or the female is a carrier. If the male and female have one child, what is the probability that the child will have cystic fibrosis? D41 1.C OM Answer: 2/3 X 2/3 X 1/4 = 1/9 PRE MED 411 .CO MPRE M ED4 11. COM - PR EME D4 11. COM - PR EME D4 11. COM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME D41 1.C OM - PR EME 5. A color-blind woman with Turner syndrome (XO) has a father who is color blind. Given that the gene for the color blind condition is recessive and X-linked, provide a likely explanation for the origin of the color blind and cytogenetic conditions in the woman. Answer: The woman inherited an Xrg chromosome from the father. Nondisjunction in the female (either at meiosis I or II) produced an egg with no X chromosome, which, when fertilized by the Xrg-bearing sperm produced the Turner syndrome condition. ...
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