HUMAN GENETICS FEBRUARY 2, 1996. EXAM 1
Mathematical Formulae:
A. general binomial formula: (A + N)n = 1
sample expansions: (A + N)2 = A2 + 2AN + N2 for n = 2
(A + N)3 = A3 + 3A2N + 3AN2 + N3 for n = 3
B. expansion formula: P(rA, sB) = (n!/r!s!) {P(A)}r{P(B)}s
where P(rA, sB) represents the probability of outcome A occurring r times and outcome B occurring s times;n is the total number of outcomes and n = r + s; P(A) is the probability of event A; P(B) is the probability of event B.
Section 1. THE CORRECT ANSWER WILL SHOW AS RED TEXT
1. In a general karyotypic survey of neonates, an infant is found to have an XYY karyotype. The parents are karyotypically normal in all tissues. They should be told
A. not to have any more children.
B. the risk of having another child with XYY is one half
C. the child will develop aggressive behavior
D. the child may have learning disorders
E. the child will develop infertility
2. Which of the following statements is TRUE about facultative heterochromatin?
A. It is transcriptionally active during interphase in some cell types.
B. It is transcriptionally active throughout all phases of the cell cycle.
C. It is transcriptionally active in all cell types.
D. It would stain G dark and Q bright if derived tissues that were transcriptionally active.
E. It would stain G dark and Q bright regardless of the transcriptional status of the tissues.
3. The stage of prophase I in which homologous chromosomes begin synapsis is called
A. zygotene
B. diplotene
C. dictyotene
D. pachytene
E. diakinesis
4. What is the most likely mode of inheritance for the following pedigree?
A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive
E. Balanced translocation
F. mitochondrial inheritance
5. If an X chromosome is lost at the first mitotic division after fertilization, what is most likely phenotype of the female infant? Assume that the zygote was 46 XX (normal karyotype) and that only one nondisjunction event occurs.
A. mosaic Turner syndrome, 45 XO/ 46 XX
B. mosaic Klinefelter, 46 XY/ 47 XXY
C. normal female, 46 XX
D. nonmosaic Turner syndrome, 45 XO
E. nonmosaic Triplo X syndrome, 47 XXX
6. Theoretically, what fraction of all possible conceptions from a mother with balanced 15q18q translocation {45, XX -15,-18 +t(15q18q)} will have Trisomy 18?
A. one third
B. one half
C. one fourth
D. one sixth
E. two thirds
7. A man with Vitamin D resistant rickets (X-linked dominant) marries a woman who is a carrier of the disease. What is the probability that they will have a daughter who is affected? (Hints: Draw a pedigree first and combine probability of disease status and sex status.)
A. 1/4
B. 1/2
C. 1/3
D. 3/4
E. 0
8. In the mitotic cell cycle, sister chromatids separate at
A. G1 phase
B. S phase
C. prophase
D. anaphase
E. telophase
9. The diagram shows two G-banded homologues; the paternal homologue is normal. The chromosome on the right contains
A. a large deletion spanning several bands
B. a large duplication spanning several bands
C. a paracentric inversion
D. a pericentric inversion
E. an isochromosome
10. Which of the following repeated DNA sequences predominate on the short arm of the human acrocentric chromosomes (e.g. 13, 14 and 15)?
A. L1 retrotransposons
B. Alu sequences
C. repeated rDNA genes
D. histone repeats
E. microsatellite DNA like CACACACACA
11. Quinacrine banding specifically stains
A. only telomeres
B. only centromeres
C. intercalary heterochromatin
D. euchromatin
E. only the long arm of the Y chromosome
12. Which of the following events could lead to the formation of a nonmosaic XYY individual? (MI = meiosis I, MII = meiosis II)
A. MI nondisjunction during spermatogenesis X normal egg
B. MII nondisjunction during spermatogenesis X normal egg
C. MI nondisjunction during oogenesis X normal sperm
D. MII nondisjunction during oogenesis X normal sperm
E. Chromosome nondisjunction at the second mitotic division of an XXY zygote.
13. A female has G6PD deficiency, an X-linked recessive trait. Which of the following genetic phenomenon would NOT explain expression of this trait?
A. Turner syndrome.
B. Extreme or unfavorable lyonization of the normal X chromosome.
C. Homozygous recessive mutations in the color vision gene.
D. Heterozygosity at color vision locus and random X inactivation.
E. Loss of the normal X chromosome in an early mitosis
14. Which of the following macromolecules would NOT be found in a 30nM chromatin fibers (also called solenoids)?
A. Histone H2A
B. Histone H2B
C. Histone H1
D. chromosomal DNA
E. scaffolding proteins
15. A man has Huntington's disease and his wife has Marfan syndrome. What is the probability that their child will exhibit both of these autosomal dominant traits?
A. 1/4
B. 1/2
C. 1
D. 1/8
E. 3/4
16. Georgia and Pete have married and are considering having children. Both are carriers (heterozygotes) of a gene defect that leads to phenylketonuria (PKU), an autosomal recessive disease. They plan to have three children, what is the probability that one will be phenotypically normal and that two will have PKU? Draw a Punnett square first!
A. 1/4
B. 3/16
C. 3/64
D. 9/64
E. 27/64
17. Which of the following karyotypes would not be found in a patient with Down syndrome?
A. 46, XY dup(21)(q22) {duplication of band q22 on
chromosome 21}.
B. 47, XX +21
C. 45, XY, -21,-22, +rob(21q22q) (chromosomes 21 and 22 are acrocentrics)
D. 46, XX, -22, + rob(21q22q)
E. 46, XX, -15, + rob(21q15q)
18. Pericentric inversions
A. change the overall length of chromosome
B. change the position of the centromere
C. change the position of the telomere
D. lead to dicentric chromosome formation after crossing overin the inversion interval
E. cause ring chromosome formation after crossing over in the inversion interval
19. What is the relationship between the structures 2 and 3 in the figure below? They are
A. sister chromatids
B. nonsister chromatids
C. homologous chromosomes
D. nonhomologous chromosomes
E. reciprocal translocations
20. David and his wife Holly are phenotypically normal carriers of a defective galactosemia gene (g) gene; gg homozygotes will develop the disease. The gene for galactosemia lies on chromosome 9. What is the probability that they will have a phenotypically normal child? Draw a Punnett square first!
A. 1/4
B. 1/3
C. 2/3
D. 3/4
E. 1
21. Which of the following structures is attached to mitotic metaphase centromeres?
A. cytoskeletal microtubules
B. astral microtubules
C. kinetochore microtubules
D. polar microtubules
E. synaptonemal complex
22. Which of the following statements is TRUE of X-linked recessive inheritance?
A. The phenotype is always manifested in female heterozygotes.
B. In large pedigrees, more females are affected than males.
C. All female offspring of an affected male will be carriers. (assuming a genotypically normal mother).
D. There is male to male transmission of the trait.
E. All offspring of both sexes of an affected mother will be phenotypically affected (assuming a genotypically normal father).
23. In the absence of a karyotype, which of the following syndromes is LEAST likely to be diagnosed in the newborn?
A. Turner Syndrome
B. Klinefelter Syndrome
C. Trisomy 18
D. Trisomy 21
E. Cri-du-Chat Syndrome
24. In the pedigree below, factor IX hemophilia, (an X-linked recessive) is segregating through three generations. Which individuals are heterozygous for the mutant gene for factor IX deficiency? Assume that the trait is rare. Open symbols are phenotypically normal, filled in symbols are phenotypically affected?
A. I-2 only
B. I-2 and II-3 only
C. I-2, II-3 and II-5 only
D. I-2, II-3, II -5 and III-2 only
E. none of the above
25. What is the most likely mode of inheritance for the following pedigree?
A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive
E. Balanced translocation
F. mitochondrial inheritance
26. Which one of the following individuals represent a nondisjunction event that could only occur at the paternal
first meiotic division. (M stands for maternal origin, P or pat for paternal). Assume normal parents.
A. 47 XM XP XP
B. 47 XM XP Y
C. 47 XM Y Y
D. 47 XM XM XP
E. 47 XY, +21pat
27. Which of the following agents is used to synchronize cells in the cell cycle?
A. Silver nitrate
B. Phytohemagglutinin
C. Hypotonic saline
D. Hypertonic saline
E. Methotrexate
28. Duplications can result from
A. recombination between paracentric inversions
B. recombination between pericentric inversions
C. misalignment followed by recombination between
normal homologues.
D. ionizing radiation
E. all of the above
29. The genes for color blindness (C locus) and clotting Factor IX (F locus) are linked on the X chromosome and are 2 cM apart). Isabella is a phenotypically normal but heterozygous (wild type/mutant) at both loci. If her alleles are in coupling, what fraction of all of her eggs will be (C, f) i.e. normal at the C locus and mutant at the F locus (HINT: Draw a map of the Isabella's two X chromosomes.)
A. 0.1 %
B. 1.0 %
C. 25 %
D. 49 %
E. 99 %
30. AluI repeats are an example of
A. interspersed middle repetitive DNA
B. interspersed low repetitive DNA
C. tandemly repeated highly repetitive DNA
D. unique sequence DNA
E. none of the above
31. A newborn female has webbing of the neck and lymphedema. Staining of cells from her buccal mucosa indicate a single Barr body, while her white blood cells have no Barr bodies at all. The most likely genotype of this individual is
A. 45 XO
B. 47 XXY
C. 47 XXX/ 46 XX
D. 47 XXX
E. 45 XO/ 46 XX
32. What is the most likely mode of inheritance for the following pedigree? Assume that I-1 is not a carrier.
A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive
E. Balanced translocation
F. mitochondrial inheritance
33. Which of the following individuals would have the greatest theoretical risk of having a child with Down Syndrome? Use viable conceptions as the denominator, not all possible conceptions.
A. 47 XX +21
B. 46,XY, -14, -21 + t(q14;q21)
C. 46,XX in somatic cells/ 47,XX +21 germline cells
D. 45,XY, -21,-21, + i(q21;q21)
E. 46,XY, -21 ,-21 +21qdup22.2, +21qdel22.2
(this is a carrier of balanced duplication of Down syndrome
critical region.)
34. Homologous chromosomes segregate from each other at
A. meiotic anaphase I only
B. meiotic anaphase II only
C. mitotic anaphase only
D. mitotic anaphase and meiotic anaphase II
E. none of the above
35. thrown out
36. Which of the following sites/structures can NOT be detected with conventional Giemsa staining?
A. Intercalary heterochromatin
B. Fragile sites
C. Replication origins
D. Satellites (the knobs, not the repeated DNA)
E. Centromeric constrictions