Bio 97, Introductory Genetics, at UC Irvine

FINAL EXAM FALL 1999

Notes for all questions:

Affected = has the disease

Unaffected = does not have the disease (but may be a carrier if the disease is recessive)

Normal = does not have the disease and is not a carrier.

For all questions, assume any trait or disease mentioned has 100% penetrance.

All diseases mentioned are genetic diseases.

Questions in Section 1 are worth 1 point. Questions in Section 2 are worth 2 points.

CORRECT ANSWERS ARE BOLD AND BLUE and marked with an asterisk *
The red numbers in parentheses show the percent of students who answered correctly e.g. (87%) for problem 1.
The mean score for this final was 31.7 out of 45 (70%). The "A" range was 38+ (84%+).

SECTION 1

1. (87%) Fill in the blanks: ___ is the genetic material. Portions of it are transcribed into ___, which is then translated into ____.

  1. RNA, DNA, protein

  2. RNA, protein, DNA

  3. Protein, RNA, DNA

  4. DNA, protein, RNA

  5. DNA, RNA, protein *

2. (62%) A male affected with Klopski’s disease mates with an unaffected female and has an affected son and an unaffected daughter. Which type(s) of inheritence can be ruled out for Klopski’s disease?

  1. Autosomal dominant

  2. X-linked dominant *

  3. Autosomal recessive

  4. X-linked recessive

  5. B, C and D

3. (62%) A female affected with Klutzki’s disease mates with an unaffected male and has an affected daughter. Which type(s) of inheritence can be ruled out for Klutzki’s disease?

  1. Autosomal dominant

  2. X-linked dominant

  3. Autosomal recessive

  4. X-linked recessive *

  5. A, B and D

4. (90%) Human somatic cells...

  1. Have 44 chromosomes: 21 pairs of autosomes plus one pair of sex chromosomes

  2. Have 46 chromosomes: 22 pairs of autosomes plus one pair of sex chromosomes *

  3. Have 48 chromosomes: 23 pairs of autosomes plus one pair of sex chromosomes

  4. Have 23 chromosomes

  5. Are usually aneuploid

5. (75%) Which of the following statements are true:

  1. All eggs produced by the same woman are genetically identical

  2. All sperm produced by the same man are genetically identical

  3. Both A and B

  4. Neither A nor B *

  5. C and D

6. (41%) Recessive alleles...

  1. Are usually X-linked

  2. Usually encode a non-functional protein or a protein with diminished function *

  3. Usually encode a protein that has gained a new function

  4. Are rapidly eliminated from the gene pool if disadvantageous

  5. C and D

7. (57%) The cross ab/ab x Ab/aB is performed. If the two genes in question are completely linked, the progeny will have the genotypes AaBb :Aabb : aaBb : aabb in the ratio...

  1. 1 : 1 : 1 : 1

  2. 1 : 0 : 0 : 1

  3. 0 : 1 : 1 : 0 *

  4. 1 : 2 : 2 : 1

  5. 9 : 3 : 3 : 1

8. (68%) Mendel’s Law of Independent Assortment holds only if the genes in question...

  1. Are on the same chromosome

  2. Are within 50 centiMorgan of each other

  3. Are unlinked *

  4. Are not subject to natural selection

  5. Are not epistatic

9. (58%) Which of the following statements is false?

  1. Any two genes on the same chromosome are linked *

  2. Crossing-over is also called meiotic recombination

  3. Double cross-overs cause an underestimation of the distance between two loci

  4. Each 1 % recombination between two linked genes suggests a distance of roughly 1 million base pairs between them

  5. None of the statements are false

10. (89%) Which of the following statements is false?

  1. In females, one copy of X is randomly inactivated in all somatic cells

  2. The most frequent cause of aneuploidy is chromosomal non-disjunction

  3. The risk of non-disjunction decreases with maternal age *

  4. Trisomy 21 is the most common live-birth aneuploidy

  5. None of the statements are false

11. (96%) The distance between genes ARR and BEA is 5 centiMorgans (cM). The distance between ARR and DUM is 8 cM. The distance between BEA and DUM is 13 cM. The order of these genes is most likely:

  1. ARR-BEA-DUM

  2. ARR-DUM-BEA

  3. BEA-ARR-DUM *

  4. Cannot be determined from the information given

  5. The three genes are clearly on different chromosomes

12. (60%) The menbers of this family have been DNA typed for a four-allele polymorphic marker. The genotype of each person with respect to the marker is shown below the pedigree symbols. Three people (filled-in symbols) are affected with an autosomal dominant disease. If the marker is closely linked to the disease gene, then the disease causing allele in Dad is on the same single chromosome as:

figure 1

  1. Allele #1 of the marker

  2. Allele #2 of the marker

  3. Allele #4 of the marker

  4. The pedigree does not support the assumption of linkage of the marker to the disease gene *

  5. None of the above, as Dad must be homozygous for the disease gene

13. (63%) Tandem repeat polymorphisms are often used for DNA fingerprinting because...

  1. They are highly polymorphic in the population *

  2. The frequency of the predominant allele is very close to 1.0

  3. They are linked to genes known to cause criminal behavior

  4. They are kept in the population because of heterozygote superiority

  5. All of the above

14. (94%) The test cross ab/ab x AB/ab is performed. The progeny have the genotypes AaBb : Aabb : aaBb : aabb in the ratio 38% : 11% : 9% : 42 %. What is the percent recombination between the two genes in question?

  1. 90 %

  2. 11 %

  3. 20 % *

  4. 47 %

  5. 2 %

15. (82%) A woman is a carrier of a Robertsonian translocation involving chromosomes 14 and 21. If she mates with a normal man and has kids, they could be...

  1. Normal

  2. Carriers, like her

  3. Aneuploid

  4. A, B or C, above *

  5. None of the above

16. (94%) Which of the following statements is true:

  1. Most aneuploid conceptions spontaneously abort

  2. Birth defects are the most common cause of infant death in the U.S.A.

  3. About one-third of all human pregnancies abort spontaneously after conception

  4. Chromosomal abnormalities are the leading known cause of pregnancy loss

  5. All of the statements (A-D) are true *

17. (90%) Which of the following is NOT a balanced rearrangement:

  1. Reciprocal Translocation

  2. Robertsonian Translocation

  3. Inversion

  4. Deletion *

  5. All of the above are balanced rearrangements

18. (60%) Which of the following statements is true:

  1. Any time DNA is damaged, a mutation will result

  2. The vast majority of DNA damage is caused by man-made chemicals and man-made radiation

  3. Hundreds of new alleles are created in each gamete as a result of replication errors

  4. Typical DNA polymerases can correct ("proofread") most of their own mistakes *

  5. All of the statements (A-D) are true

19. (60%) A woman does a lot of tanning without sunscreen in high school and college. At age 40, she developes malignant melanoma (skin cancer). A sample of one of her tumors is taken, as well as a sample of her blood. DNA is prepared from both samples and the sequence of the coding region of the p53 gene is compared. The following difference is found:

Blood: 5’-ATGCAAGTTCTA Tumor: 5’-ATGCAAGTCTA

This is an example of:

  1. Silent substitution

  2. Missense substitution

  3. Nonsense substitution

  4. Frameshift *

  5. None of the above

20. (77%) A tall man and a short woman mate and have an average sized kid. This is consistent with the concept that...

  1. Mendel was wrong; alleles do not segragate, they blend together

  2. height is a multifactorial trait *

  3. height is subject to heterozygote superiority

  4. the kid has a sex chromosome aneuploidy

  5. height is determined by the environment, not by genes

21. (80%) Which of the following events is NOT likely to contribute to carcinogenesis:

  1. A mutation that inactivates the cell suicide program

  2. A mutation that deregulates the cell cycle

  3. A mutation that inactivates a DNA repair enzyme

  4. Voluntary exposure to a mutagenic agent (e.g. tobacco smoke)

  5. All of the above (A-D) are likely to contribute to carcinogenesis*

22. (62%) Betsy and Boopsie are half sisters (same mom, different dad). Boopsie has a son named Bobby. The proportion of their alleles that Betsy and Bobby have in common is, on average:

  1. 1/2

  2. 3/8

  3. 1/4

  4. 1/8 *

  5. 1/16

23. (68%) Which of the following would NOT be expected to cause allele frequencies to vary over time:

  1. Migration

  2. Random mating *

  3. Mutation

  4. Genetic Drift

  5. Natural selection

24. (63%) Children and young adults get leukemia relatively frequently, whereas lung cancer is mainly a disease of older adults. The most likely explanation for this is:

  1. Young adults smoke more than older adult

  2. Increased risk of non-disjunction in older adults

  3. Leukemia requires mutations in fewer distinct genes than does lung cancer *

  4. Children have fewer tumor suppressor genes

  5. Higher mutation rate in children and young adults

25. (65%) An x-linked recessive disease, caused by a single gene, affects in 1/25 men (1 in 25 = 0.04). What is the frequency of affected females (assume Hardy-Weinberg can be applied)

  1. 0.0016 *

  2. 0.04

  3. 0.2

  4. 0.32

  5. 0.64

SECTION 2

26 & 27. (87%) Which of the following statements is FALSE

  1. If a female carrier of an X-linked recessive disease mates with a normal man, half of her sons will be affected, on average

  2. If a female carrier of an X-linked recessive disease mates with a normal man, half of her daughters will be carriers, on average

  3. If a male affected with an X-linked recessive disease mates with a normal woman, all of his sons will be norma

  4. If a male affected with an X-linked recessive disease mates with a normal woman, all of his daughters will be carriers

  5. None of the statements are false *

28 & 29. (70%) An unaffected couple has a daughter affected with Koopski’s disease. Which type(s) of inheritence can be ruled out for Koopski’s disease?

  1. Autosomal dominant

  2. X-linked dominant

  3. Autosomal recessive

  4. X-linked recessive

  5. A, B and D *

30 & 31. (63%) Sam and Sally are two unrelated people affected with retinitis pigmentosa (RP), a hereditary disease causing blindness. Both of Sam’s parents, and both of Sally’s parents, are unaffected. Sam and Sally marry and have 4 normal children. How could this have happened?

  1. RP is an x-linked recessive disease and the four kids must have been girls

  2. RP exhibits locus heterogeneity: Sam and Sally are homozygous for disease-causing alleles at different loci *

  3. Three-fourths of their kids, on average, should have been affected. They just got very lucky

  4. One-fourth of their kids, on average, should have been affected. They just got a little lucky

  5. RP is a multifactorial trait

32 & 33. (75%) A man is born with the karyotype 47, XYY. The most likely explanation for this is:

  1. Non-disjunction during meiosis I in his father

  2. Non-disjunction during meiosis II in his father *

  3. Non-disjunction during meiosis I in his mother

  4. Non-disjunction during meiosis II in his mother

  5. Unequal crossing-over

34 & 35. (88%) The test cross ab/ab x AB/ab is performed. The following number of progeny of each genotype are obtained: 360 AaBb, 120 Aabb, 130 aaBb, 390 aabb. What is the distance (im map units) between the two genes in question?

  1. 25 centiMorgans (cM) *

  2. 20 cM

  3. 15 cM

  4. 10 cM

  5. 5 cM

36 & 37. (31%) DNA samples are taken from two people (#1 and #2), and analyzed by restriction digestion, agarose gel electrophoresis and Southern blotting, using as a probe a DNA sequence that is part of the CD40 gene. The sample from Person #1 shows a single band of 6.0 kb. The sample from Person #2 shows this band, and also two other bands: one of 2.5 and one of 3.5 kb. The most likely explanation for this result is:

  1. Person #1 is monosomic for the chromosome the marker is on

  2. Person #2 is trisomic for the chromosome the marker is on

  3. Person #1 is heterozygous for a restriction-fragment length polymorphism at the CD40 locus

  4. Person #2 is heterozygous for a restriction-fragment length polymorphism at the CD40 locus *

  5. CD40 is an oncogene

38 & 39. (35%) A single mutation occurs in the coding region of a gene and results in a non-functional gene product (protein). The type of mutation that most likely occurred (becase it is the type most likely to result in a non-functional gene product) is:

  1. Missense or silent

  2. Missense or nonsense

  3. Missense or frameshift

  4. Nonsense or frameshift *

  5. Silent or nonsense

40 & 41. (92%) An autosomal recessive disease, caused by a single gene, affects 1/100 (1 in 100 = 0.01) people in the population. What is the frequency of heterozygous carriers in this population (assume Hardy-Weinberg can be applied).

  1. 0.0001

  2. 0.01

  3. 0.18 *

  4. 0.25

  5. 0.81

42 & 43. (92%) The members of this family have been DNA typed for a three-allele polymorphic marker. The genotype of each person with respect to the marker is shown below the pedigree symbols. Three people (filled-in symbols) are affected with an autosomal dominant disease. Assuming that the marker is closely linked to the disease gene, then the disease causing allele in Dad is on the same single chromosome as

figure 2

  1. Allele #1 of the marker

  2. Allele #2 of the marker *

  3. Allele #3 of the marker

  4. The pedigree does not support the assumption of close linkage of the marker to the disease gene

  5. None of the above, as Dad must be homozygous for the disease gene

44 & 45. (32%) Hereditary retinoblastoma is an inherited predispostion to retinal cancer. It is caused by a mutation in the RB gene. The disease causing allele (R) is dominant to the normal allele (r); kids who are Rr heterozygotes develop multiple tumors in both eyes. However, sequencing of R alleles indicates that they encode non-functional proteins. Furthermore, sequencing of tumor tissue from kids who are Rr heterozygotes reveals that the tumor cells are now homozygous RR. A reasonable explanation is that...

  1. RB encodes a DNA repair enzyme, so there’s increased DNA damage and mutagenesis in Rr heterozygotes

  2. A somatic mutation occurs in the normal copy of the RB tumor suppressor gene in some cells of the developing retina. These cells go on to become tumors *

  3. RB encodes a dominant oncogene

  4. RB is a transposable element

  5. RB exhibits locus heterogeneity